Re: QMX RF power line diode switches
Evan, thanks for the pointer. That document is an excellent description of the design.
There are two statements that I am not fully convinced, though.
- the voltage doubler produces a voltage greater than the Vp-p of the RF power
- the bias voltage is always ahead of the RF power envelope while the power is taperd up or down.
Yeah I understand what you are saying but the scope of this thread is the switching behavior during TX so I omitted the details for the RX state.
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John,
Regardless if you have any new ideas, I very much appreciate your efforts. I've learned some things along the way so it's been good that way.
I'll keep looking and pondering and playing. We'll see what comes up. In worse case I'll order another kit. It's sad that this one that was working so well, has become a problem child, but that's life in electronics sometimes.
toggle quoted message
Show quoted text
Cliff,
I am not seeing clear signals here regarding your failure scenario.
That really annoys me, but that's life...
I could conjure up some complex sketchy failure stories but I would have zero confidence in them.
Retrenching for a deep think.? I may be back later.
If not, I have given up.
JZ KJ4A?
John, thanks for the reply.
Answers to your questions:
This time it was the same as last time, Q504. The time before last it was Q505.
SWR was 1.0 according to my QRP SWR/Dummy load.
Current draw on 20M was about 800ma for 4 watts using 11V. Going to 12V I get almost half a watt more out with only slightly more current draw.. 40M about 175ma with slightly lower output power.
Yes on the thermal paste and yes, socketed PA transistors. I've considered removing the sockets, but the board isn't going to last long changing finals like I have been without sockets.
With it out of the case the display board area over the finals was warmer than I expected, but not hot. Hard to find hot spots with the display board installed. I suppose I could try transmitting with the display board off and see what I find.
Screw was not really tight. Just enough to hold some light pressure on the board. I suppose I could leave it even more loose.
The PCB looks very smooth and the transistor is not cracked, at least not that I can see with 10x mag Loupe.
A month ago I did have one crack, actually heard the crack. It separated into 2 pieces. That's the only time though.
I don't think this could factor into the issue, but a while back I added a turn to L513 because squeezing the windings helped and the power was still lower than the other bands. Rewound it and now the power is about 1/2 watt higher than the other bands.
Cliff, darn, sorry to hear that!
Did you note which BS170 blew? Was it same or different from last time? I presume you checked SWR and it was OK? What current draw were you seeing from the PS in xmit?
Your failure sounds like it could be heat related.? Do you use thermal compound under the BS170s? IIRC you socketed the PA transistors.
Is anything else in the box dumping too much heat?
When you reassembled the washer, nut and screw that hold down on the PA transistors, did you leave the nut just finger tight, or did you torque down on it? Are there any stress concentrating irregularities on the PCB surface under the PA transistors? Has the case of the failed transistor cracked?
Yes, many questions...
JZ Hi John,
Well, I hoped it was fixed, but apparently not.?
Just blew at least one BS170. Had it all assembled, but outside the case. Worked for about and hour of transmit time, most of that on FT8. It was happily working a station when the current draw went up to max current limiting. Powered down and pulled the finals and all is fine current wise. Verified drive voltages on the gates - all 2.5V in TX and zero on RX.
Q507 still checks good.
This is getting frustrating.? Of course I blame myself for so stressing the rig the first time it blew a final by not noticing the high current draw for a while. The question in my mind is whether the stress damaged something or what ever caused the first one blown BS170 is the issue.? Would still like to fix it though, but can't forever keep throwing BS170s at it either.
Don't feel like it's your responsibility to find the issue, but I do very much appreciate your insights into the circuits and suggestions.
OK Cliff!I'm glad you have it working. I just wish we knew exactly what hadhappened to Q507.JZOn Sat, Sep 23, 2023 at 8:37?PM Cliff <ae5zaham@...> wrote:
Hi John,
Well to pick up the thread we had earlier, I got a new Q507 and installed it.
Tested the modulator for being on based on what Hans said about the fact that before the first transmission the drain shows high, then shuts the modulator off after the first transmission. It does exactly that so apparently the modulator is fine, i.e. not on as we thought, at at least.
Now the gate is 11v before the first transmission then 0.3 after transmission. Maybe the Q507 was bad after all?
Anyway it's working again. Wonder how long the finals will last this time. Hmmm....
Hopefully it's fixed now, but I won't know until I use it for a while.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:48, Cliff <ae5zaham@...> wrote:
John,
Thanks for the explanation. I fully understand. No controversy here.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:40, John Z <jdzbrozek@...> wrote:
Cliff,
Sorry to hear about the busted FET!
The modulator in QMX serves a number of special functions that QDX does not require.
CW wave shaping, to eliminate annoying ?transmitted key clicks, is one example.
Someday it will be used to create. synthetic SSB.
Hans also uses it to gracefully wind down the transmit power at the end of each transmission. That should avoid a damaging Ldi/dt spike from the PA's power feed inductor.
QDX does not benefit from that spike protection, as it has no modulator circuit. Hence, you will see discussions about the use of commutating diodes, zener diodes, or other means to protect the QDX finals.
These discussions always seem to drag along some controversy. There should be none. The Ldi/dt spike is real and it puts the PA transistors into a dangerous out-of-spec condition.
JZ KJ4A
On Tue, Sep 19, 2023, 2:14 PM Cliff <ae5zaham@...> wrote:
John,
Looking at the schematic for the QDX there is no modulator like the QMX and the L14 which is similar to the L507 in function is always at the input voltage, 11V in this case. At least in the QDX it's normal to have the input voltage on that coil all the time, but I guess not in the QMX.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 11:34, Cliff <ae5zaham@...> wrote:
Thanks John,
Well, the gate had 6.5V on it. The Source and Drain had 11V. Wasn't sure whether that was 6.5 was high or low. Low I was expecting to be 0V. I lifted the Gate pin and now the pad for the gate is still 6 V, but the Drain is 5.4 and the Source is still 11V. It appears as if Q507 was being turned on. Interesting with the gate disconnected from the pad the idle current drain still hasn't dropped. Seems as if that wasn't causing an increase in receive current.
What do you think?
73,
Cliff, AE5ZA
On Sep 19, 2023, at 00:07, John Z <jdzbrozek@...> wrote:
Cliff,
You have confirmed that there is a problem at the PMOSFET modulator.
When all the BS170 are good, they are all off in receive mode and you can expect a normal receive current level even if the modulator is stuck "on". When one or more have failed, a stuck modulator will allow elevated receive current.
Your reading of 11 volts during receive is proof that the modulator is turned on, wrongly.
The next step is to measure the gate voltage at Q507 in receive. If it is low, Q507 is being driven on by the four 'difference amplifier' transistors that compare the DAC signal from the processor to the output of the modulator and produce the gate drive signal for Q507. Determining which have failed would be the next challenge.
If the gate voltage us high, and Q507 is conducting, Q507 is shorted.
...
I see a preceding post that goes on a remarkable run-on over your use of sockets. There is a grain of truth in there, amongst several misconceptions, in that socketing does somewhat impede heat flow out the leads of the BS170. That was neither your initial problem nor your biggest problem now.
In the future I would advise a thin layer of thermal compound under the transistors, and between them and the washer. too. Do not over tighten the nut and screw as thermally expanding transistors will be squeezed badly.
The molded case of modern TO-92 transistors contains a thermally conductive filler to allow the case to participate in heat rejection. The via holes that pepper the plated pad that the transistors sit upon are not helping that at all. They impart surface irregularities ( and hence air gaps) that get in the way of good heat rejection. A little thermal compound helps overcome that.
Good luck, JZ KJ4A
On Mon, Sep 18, 2023, 11:14 PM Cliff <ae5zaham@...> wrote:
Good thoughts JZ.
When I see the idle current go up I open things up and find one of the BS170s is causing it. Pull the bad one and it goes back to normal receive (idle) current so I doubt that the modulator is on, but will verify it anyway.
In receive has 11V on it. Does that mean that Q507 is bad? Sorry I'm not familiar with how Mosfets work? Could the very bad current draw when I had left off the antenna caused that? That looks like a pain to remove without a hot air rework system which I don't have.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 21:05, John Z <jdzbrozek@...> wrote:
Cliff,
I think you are correct when you suggest that something more is going on with the rig.
I suspect that the PMOSFET modulator may be stuck "on". It would not afford protection against destructive Ldi/dt spikes from L502 if it were stuck.
You mention idle current going up when BS170s fail. I presume that you mean current drawn while in receive. That would be another indication of a fault in the modulator section. The modulator should take PA current to zero in receive.
If you see voltage on L502 during receive, that would confirm a stuck modulator.
You might be able to go further in diagnosis using just a multimeter, but at that point it may be better to send your QMX to Jeffrey W. Moore for repair.
JZ KJ4A
On Mon, Sep 18, 2023, 8:46 PM Cliff <ae5zaham@...> wrote:
Hi Paul,
Thanks for the response.
I've had it fail while in different modes. Olivia usually has the longest key down times since it's quite slow. This last time I was in Feld Hell which is one of the easiest modes there are on the rig. It's not a constant transmission, but many with very short pauses mixed in. The rig had been sitting for several hours so it wasn't even hot.
No scope here, sad to say. Testing the Q503 with digital VM and verified 2.5 volts on all final gates.
You raise an interesting point about spikes. Maybe the first time it was damaged was bad enough that it damaged something so there are spikes that are damaging the finals. What that would be I don't know, but maybe one of the experts on this list may have an idea.
Power and SWR are the same on a dummy load. Could try simulating a QSO with the dummy load, but it might take a long time to get enough time on the rig to act up.
The Power/SWR Meter is built into the dummy load and is in between the tuner and the rig so I take it the SWR is what the rig sees. Putting the SWR meter after the tuner shows 1.3:1 SWR. Tuning with the LED indicator in tune mode ends up with the same settings on the tuner and the current draw is the same so I assume power out is the same also.
I agree, something I/we don't understand is going on.
As it is now I'm getting reticent to use the QMX as it's unreliable these days. I have 2 QDX rigs I could use, but prefer the QMX if it can be made reliable by figuring out what is wrong. Of course future firmware upgrades should make it even better.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 18:04, Paul - AI7JR <paul.hanchett@...> wrote:
You mentioned Olivia-- Is that the predominate mode here? Were there other modes where you had a problem? You mention 8-10 minute key-downs, is that typical of your operations?
Are you able to confirm proper waveforms on the gates and drains of the BS170's? No spikes, proper voltages?
Could you simulate a QSO into a dummy load, do the currents look the same? You mention the SWR is 1.0, is the load impedance presented to the QMX actually 50 ohms, or something else? (Could it be that the output impedance of the QMX isn't really 50 ohms --likely, really-- and when we adjust for 1:1 SWR, maybe the antenna isn't being adjusted to be 50 ohms?)
Your experience suggests to me that we don't understand everything about what's going on!
Paul -- AI7JR
On 9/18/23 14:53, Cliff wrote:
I built this QMX within a a month of the release of the kit. It worked great for 2 1/2 months or so. Solid even with long key down modes of 8 to 10 minutes. Power out about 4 watts.? Then I unknowingly left the antenna disconnected and called CQ 3 or 4 times in Olivia mode. I happened to look at the Buck/Boost Converter and noticed it was in current limiting mode so immediately shut off the power. Damage done. <Sigh .....>
I installed sockets for the finals and replaced all 4 BS170s and the driver IC503. Worked fine for an hour or maybe 2, btw SWR is 1.0 with a manual tuner. Then, with the antenna attached, it again blew a final during a QSO and showed current limiting. Replaced the bad BS170 and all seemed fine. IC503 looked good. This scenario ?has repeated a number of times now. Replace the bad BS170, check IC503 and it'll run fine for an hour or two of QSOs. I even replaced IC503 and all the finals again just to be sure all was ok.
I've also seen twice where the idle current increased from 130 to 200 ma. That was an indicator of a bad BS170 also.
I'm being forced to conclude that there is something else going on besides the finals just dying because of operator error. All parts are from Mouser so quality should be good. Power out is still about 4 - 4.2 watts. Current is about 750 ma, sometimes nearly 800ma (the increase puzzles me) and voltage is 11.0 volts. SWR is 1.0.
No physical shorts that I can see. It's also not always the same BS170 position that goes bad. The time before last it was Q505 and just now it was Q504.
I sure hope someone has an idea of what can be going on. I've been running out of the case to be sure it wasn't heat build up.
Any and all suggestions welcome.
Thanks.
73,
Cliff, AE5ZA
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Thanks for the info Barb. I ordered one today and will do a VNA scan when it arrives. Can¡¯t expect perfection at that price point.?
Tony
On Mon, Sep 25, 2023 at 12:27 PM < wb2cba@...> wrote: On Mon, Sep 25, 2023 at 10:03 AM, Tony Scaminaci wrote:
Wow, you can't beat the price! Barb, have you scanned these for harmonic rejection? I'd like to pick up some of these if they meet FCC specs.
?
Tony
AC9QY
On Mon, Sep 25, 2023 at 11:58?AM < wb2cba@...> wrote:
I use these:
Zyyini Low Pass Filter Module, Power Distribution Control Equipment, Wide Operating Frequency Range£¬ for RF Signals
These have a pretty good response on 70m.
73
Barb WB2CBA
?
?
Tony,
Couple of years ago I built cubesat ground stations with these. They worked pretty good.
They are kinda hit and miss but not that off from FCC parameters. It¡¯s easy to tune them just by playing with inductors, sqeeze or extend, using a vna or spectrum analyser. I didn¡¯t even have to try cap replacement.?
73
Barb WB2CBA
?
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Re: QMX RF power line diode switches
Ryuji,
To be clear, the reverse voltage is the higher of the voltage doubled peak of the transmitter (varies with the power out) OR the input voltage (mainly for receive and until the transmitter generates power).? One of the manuals may describe how that works (most likely the 50-watt PA).
I found a good description in section 6 of the 50-watt PA assembly manual
73
Evan
AC9TU
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Didn't even build the kit yet, but, Good on the 9 volts!!!
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Re: QMX RF power line diode switches
So the reverse bias is actually generated from the RF output transformer, not a fixed voltage, so it is not like having a fixed reverse bias. Analysis continues....
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Re: QMX RF power line diode switches
This is a question of the power amp output voltage swing vs the diode reverse voltage. Not the circuit topology or the diode choose. Depending on the vdssat and Ron of the final transistor the RF voltage can swing bigger than with some other transistors.
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Cliff,
I am not seeing clear signals here regarding your failure scenario.
That really annoys me, but that's life...
I could conjure up some complex sketchy failure stories but I would have zero confidence in them.
Retrenching for a deep think.? I may be back later.
If not, I have given up.
JZ KJ4A?
John, thanks for the reply.
Answers to your questions:
This time it was the same as last time, Q504. The time before last it was Q505.
SWR was 1.0 according to my QRP SWR/Dummy load.
Current draw on 20M was about 800ma for 4 watts using 11V. Going to 12V I get almost half a watt more out with only slightly more current draw.. 40M about 175ma with slightly lower output power.
Yes on the thermal paste and yes, socketed PA transistors. I've considered removing the sockets, but the board isn't going to last long changing finals like I have been without sockets.
With it out of the case the display board area over the finals was warmer than I expected, but not hot. Hard to find hot spots with the display board installed. I suppose I could try transmitting with the display board off and see what I find.
Screw was not really tight. Just enough to hold some light pressure on the board. I suppose I could leave it even more loose.
The PCB looks very smooth and the transistor is not cracked, at least not that I can see with 10x mag Loupe.
A month ago I did have one crack, actually heard the crack. It separated into 2 pieces. That's the only time though.
I don't think this could factor into the issue, but a while back I added a turn to L513 because squeezing the windings helped and the power was still lower than the other bands. Rewound it and now the power is about 1/2 watt higher than the other bands.
Cliff, darn, sorry to hear that!
Did you note which BS170 blew? Was it same or different from last time? I presume you checked SWR and it was OK? What current draw were you seeing from the PS in xmit?
Your failure sounds like it could be heat related.? Do you use thermal compound under the BS170s? IIRC you socketed the PA transistors.
Is anything else in the box dumping too much heat?
When you reassembled the washer, nut and screw that hold down on the PA transistors, did you leave the nut just finger tight, or did you torque down on it? Are there any stress concentrating irregularities on the PCB surface under the PA transistors? Has the case of the failed transistor cracked?
Yes, many questions...
JZ Hi John,
Well, I hoped it was fixed, but apparently not.?
Just blew at least one BS170. Had it all assembled, but outside the case. Worked for about and hour of transmit time, most of that on FT8. It was happily working a station when the current draw went up to max current limiting. Powered down and pulled the finals and all is fine current wise. Verified drive voltages on the gates - all 2.5V in TX and zero on RX.
Q507 still checks good.
This is getting frustrating.? Of course I blame myself for so stressing the rig the first time it blew a final by not noticing the high current draw for a while. The question in my mind is whether the stress damaged something or what ever caused the first one blown BS170 is the issue.? Would still like to fix it though, but can't forever keep throwing BS170s at it either.
Don't feel like it's your responsibility to find the issue, but I do very much appreciate your insights into the circuits and suggestions.
OK Cliff!I'm glad you have it working. I just wish we knew exactly what hadhappened to Q507.JZOn Sat, Sep 23, 2023 at 8:37?PM Cliff <ae5zaham@...> wrote:
Hi John,
Well to pick up the thread we had earlier, I got a new Q507 and installed it.
Tested the modulator for being on based on what Hans said about the fact that before the first transmission the drain shows high, then shuts the modulator off after the first transmission. It does exactly that so apparently the modulator is fine, i.e. not on as we thought, at at least.
Now the gate is 11v before the first transmission then 0.3 after transmission. Maybe the Q507 was bad after all?
Anyway it's working again. Wonder how long the finals will last this time. Hmmm....
Hopefully it's fixed now, but I won't know until I use it for a while.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:48, Cliff <ae5zaham@...> wrote:
John,
Thanks for the explanation. I fully understand. No controversy here.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:40, John Z <jdzbrozek@...> wrote:
Cliff,
Sorry to hear about the busted FET!
The modulator in QMX serves a number of special functions that QDX does not require.
CW wave shaping, to eliminate annoying ?transmitted key clicks, is one example.
Someday it will be used to create. synthetic SSB.
Hans also uses it to gracefully wind down the transmit power at the end of each transmission. That should avoid a damaging Ldi/dt spike from the PA's power feed inductor.
QDX does not benefit from that spike protection, as it has no modulator circuit. Hence, you will see discussions about the use of commutating diodes, zener diodes, or other means to protect the QDX finals.
These discussions always seem to drag along some controversy. There should be none. The Ldi/dt spike is real and it puts the PA transistors into a dangerous out-of-spec condition.
JZ KJ4A
On Tue, Sep 19, 2023, 2:14 PM Cliff <ae5zaham@...> wrote:
John,
Looking at the schematic for the QDX there is no modulator like the QMX and the L14 which is similar to the L507 in function is always at the input voltage, 11V in this case. At least in the QDX it's normal to have the input voltage on that coil all the time, but I guess not in the QMX.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 11:34, Cliff <ae5zaham@...> wrote:
Thanks John,
Well, the gate had 6.5V on it. The Source and Drain had 11V. Wasn't sure whether that was 6.5 was high or low. Low I was expecting to be 0V. I lifted the Gate pin and now the pad for the gate is still 6 V, but the Drain is 5.4 and the Source is still 11V. It appears as if Q507 was being turned on. Interesting with the gate disconnected from the pad the idle current drain still hasn't dropped. Seems as if that wasn't causing an increase in receive current.
What do you think?
73,
Cliff, AE5ZA
On Sep 19, 2023, at 00:07, John Z <jdzbrozek@...> wrote:
Cliff,
You have confirmed that there is a problem at the PMOSFET modulator.
When all the BS170 are good, they are all off in receive mode and you can expect a normal receive current level even if the modulator is stuck "on". When one or more have failed, a stuck modulator will allow elevated receive current.
Your reading of 11 volts during receive is proof that the modulator is turned on, wrongly.
The next step is to measure the gate voltage at Q507 in receive. If it is low, Q507 is being driven on by the four 'difference amplifier' transistors that compare the DAC signal from the processor to the output of the modulator and produce the gate drive signal for Q507. Determining which have failed would be the next challenge.
If the gate voltage us high, and Q507 is conducting, Q507 is shorted.
...
I see a preceding post that goes on a remarkable run-on over your use of sockets. There is a grain of truth in there, amongst several misconceptions, in that socketing does somewhat impede heat flow out the leads of the BS170. That was neither your initial problem nor your biggest problem now.
In the future I would advise a thin layer of thermal compound under the transistors, and between them and the washer. too. Do not over tighten the nut and screw as thermally expanding transistors will be squeezed badly.
The molded case of modern TO-92 transistors contains a thermally conductive filler to allow the case to participate in heat rejection. The via holes that pepper the plated pad that the transistors sit upon are not helping that at all. They impart surface irregularities ( and hence air gaps) that get in the way of good heat rejection. A little thermal compound helps overcome that.
Good luck, JZ KJ4A
On Mon, Sep 18, 2023, 11:14 PM Cliff <ae5zaham@...> wrote:
Good thoughts JZ.
When I see the idle current go up I open things up and find one of the BS170s is causing it. Pull the bad one and it goes back to normal receive (idle) current so I doubt that the modulator is on, but will verify it anyway.
In receive has 11V on it. Does that mean that Q507 is bad? Sorry I'm not familiar with how Mosfets work? Could the very bad current draw when I had left off the antenna caused that? That looks like a pain to remove without a hot air rework system which I don't have.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 21:05, John Z <jdzbrozek@...> wrote:
Cliff,
I think you are correct when you suggest that something more is going on with the rig.
I suspect that the PMOSFET modulator may be stuck "on". It would not afford protection against destructive Ldi/dt spikes from L502 if it were stuck.
You mention idle current going up when BS170s fail. I presume that you mean current drawn while in receive. That would be another indication of a fault in the modulator section. The modulator should take PA current to zero in receive.
If you see voltage on L502 during receive, that would confirm a stuck modulator.
You might be able to go further in diagnosis using just a multimeter, but at that point it may be better to send your QMX to Jeffrey W. Moore for repair.
JZ KJ4A
On Mon, Sep 18, 2023, 8:46 PM Cliff <ae5zaham@...> wrote:
Hi Paul,
Thanks for the response.
I've had it fail while in different modes. Olivia usually has the longest key down times since it's quite slow. This last time I was in Feld Hell which is one of the easiest modes there are on the rig. It's not a constant transmission, but many with very short pauses mixed in. The rig had been sitting for several hours so it wasn't even hot.
No scope here, sad to say. Testing the Q503 with digital VM and verified 2.5 volts on all final gates.
You raise an interesting point about spikes. Maybe the first time it was damaged was bad enough that it damaged something so there are spikes that are damaging the finals. What that would be I don't know, but maybe one of the experts on this list may have an idea.
Power and SWR are the same on a dummy load. Could try simulating a QSO with the dummy load, but it might take a long time to get enough time on the rig to act up.
The Power/SWR Meter is built into the dummy load and is in between the tuner and the rig so I take it the SWR is what the rig sees. Putting the SWR meter after the tuner shows 1.3:1 SWR. Tuning with the LED indicator in tune mode ends up with the same settings on the tuner and the current draw is the same so I assume power out is the same also.
I agree, something I/we don't understand is going on.
As it is now I'm getting reticent to use the QMX as it's unreliable these days. I have 2 QDX rigs I could use, but prefer the QMX if it can be made reliable by figuring out what is wrong. Of course future firmware upgrades should make it even better.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 18:04, Paul - AI7JR <paul.hanchett@...> wrote:
You mentioned Olivia-- Is that the predominate mode here? Were there other modes where you had a problem? You mention 8-10 minute key-downs, is that typical of your operations?
Are you able to confirm proper waveforms on the gates and drains of the BS170's? No spikes, proper voltages?
Could you simulate a QSO into a dummy load, do the currents look the same? You mention the SWR is 1.0, is the load impedance presented to the QMX actually 50 ohms, or something else? (Could it be that the output impedance of the QMX isn't really 50 ohms --likely, really-- and when we adjust for 1:1 SWR, maybe the antenna isn't being adjusted to be 50 ohms?)
Your experience suggests to me that we don't understand everything about what's going on!
Paul -- AI7JR
On 9/18/23 14:53, Cliff wrote:
I built this QMX within a a month of the release of the kit. It worked great for 2 1/2 months or so. Solid even with long key down modes of 8 to 10 minutes. Power out about 4 watts.? Then I unknowingly left the antenna disconnected and called CQ 3 or 4 times in Olivia mode. I happened to look at the Buck/Boost Converter and noticed it was in current limiting mode so immediately shut off the power. Damage done. <Sigh .....>
I installed sockets for the finals and replaced all 4 BS170s and the driver IC503. Worked fine for an hour or maybe 2, btw SWR is 1.0 with a manual tuner. Then, with the antenna attached, it again blew a final during a QSO and showed current limiting. Replaced the bad BS170 and all seemed fine. IC503 looked good. This scenario ?has repeated a number of times now. Replace the bad BS170, check IC503 and it'll run fine for an hour or two of QSOs. I even replaced IC503 and all the finals again just to be sure all was ok.
I've also seen twice where the idle current increased from 130 to 200 ma. That was an indicator of a bad BS170 also.
I'm being forced to conclude that there is something else going on besides the finals just dying because of operator error. All parts are from Mouser so quality should be good. Power out is still about 4 - 4.2 watts. Current is about 750 ma, sometimes nearly 800ma (the increase puzzles me) and voltage is 11.0 volts. SWR is 1.0.
No physical shorts that I can see. It's also not always the same BS170 position that goes bad. The time before last it was Q505 and just now it was Q504.
I sure hope someone has an idea of what can be going on. I've been running out of the case to be sure it wasn't heat build up.
Any and all suggestions welcome.
Thanks.
73,
Cliff, AE5ZA
|
Re: QMX RF power line diode switches
On Mon, Sep 25, 2023 at 05:31 PM, Ryuji Suzuki AB1WX wrote:
At that point I think the RF amp output is practically shorted to the ground unless operating on the lowest band of the filter bank and may blow the finals.
If real PIN diodes are used this would be almost nonissue but with a rectifier pn junction the reverse bias voltage is often the limiting factor.
Might I suggest Ryuji that you do a little research before yet another blanket statement about this design. I am am becoming a little bored with your constant rubbishing. However if you are in the midst of an entirely new radio design which will knock QRP labs into a cocked hat, I really cannot wait to see it. Ted??
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Possibly by G4JNT in RadCom.
toggle quoted message
Show quoted text
On 25 Sep 2023, at 15:26, Bob Parr < parr@...> wrote:
I have lots of wall warts.? I may be remembering wrong, but I thought there was an article or amendment on one or several of the install instructions on either a power supply filter or how to build a power supply... maybe it was just an "good to know" about power supplies.
Bob
KG5GTE
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Re: QMX RF power line diode switches
Ryuji,
Hans uses the same switching mechanism, including the voltage doubler, for the RX/TX switching on his 50W PA. ?So the general theory is in use up to at least that power level. ?Both QMX and the 50W PA use 1N4007 diodes.
Jonathan KN6LFB
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Re: QMX RF power line diode switches
Thanks JZ. I just don¡¯t want to find out the limits at 3000 feet elevation and hours away from my bench.
I think with a pair of high performance RF transistors and 1:1 output transformer, there may not be enough safety margin at any supply voltage if the diodes are reverse biased at -2Vcc. If the rev bias can¡¯t be increased, I might have to drop the final stage supply voltage with series diodes to create the margin.
If anyone else finds their favorite final transistor, be careful high performance choices will run into this issue quickly. If the high band transmit power performance is worse than lower bands I¡¯d carefully look into heavy load situation by unwanted conduction. LPF input above the cutoff frequency will look shorted to ground from the source.
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John, thanks for the reply.
Answers to your questions:
This time it was the same as last time, Q504. The time before last it was Q505.
SWR was 1.0 according to my QRP SWR/Dummy load.
Current draw on 20M was about 800ma for 4 watts using 11V. Going to 12V I get almost half a watt more out with only slightly more current draw.. 40M about 175ma with slightly lower output power.
Yes on the thermal paste and yes, socketed PA transistors. I've considered removing the sockets, but the board isn't going to last long changing finals like I have been without sockets.
With it out of the case the display board area over the finals was warmer than I expected, but not hot. Hard to find hot spots with the display board installed. I suppose I could try transmitting with the display board off and see what I find.
Screw was not really tight. Just enough to hold some light pressure on the board. I suppose I could leave it even more loose.
The PCB looks very smooth and the transistor is not cracked, at least not that I can see with 10x mag Loupe.
A month ago I did have one crack, actually heard the crack. It separated into 2 pieces. That's the only time though.
I don't think this could factor into the issue, but a while back I added a turn to L513 because squeezing the windings helped and the power was still lower than the other bands. Rewound it and now the power is about 1/2 watt higher than the other bands.
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Show quoted text
Cliff, darn, sorry to hear that!
Did you note which BS170 blew? Was it same or different from last time? I presume you checked SWR and it was OK? What current draw were you seeing from the PS in xmit?
Your failure sounds like it could be heat related.? Do you use thermal compound under the BS170s? IIRC you socketed the PA transistors.
Is anything else in the box dumping too much heat?
When you reassembled the washer, nut and screw that hold down on the PA transistors, did you leave the nut just finger tight, or did you torque down on it? Are there any stress concentrating irregularities on the PCB surface under the PA transistors? Has the case of the failed transistor cracked?
Yes, many questions...
JZ Hi John,
Well, I hoped it was fixed, but apparently not.?
Just blew at least one BS170. Had it all assembled, but outside the case. Worked for about and hour of transmit time, most of that on FT8. It was happily working a station when the current draw went up to max current limiting. Powered down and pulled the finals and all is fine current wise. Verified drive voltages on the gates - all 2.5V in TX and zero on RX.
Q507 still checks good.
This is getting frustrating.? Of course I blame myself for so stressing the rig the first time it blew a final by not noticing the high current draw for a while. The question in my mind is whether the stress damaged something or what ever caused the first one blown BS170 is the issue.? Would still like to fix it though, but can't forever keep throwing BS170s at it either.
Don't feel like it's your responsibility to find the issue, but I do very much appreciate your insights into the circuits and suggestions.
OK Cliff!I'm glad you have it working. I just wish we knew exactly what hadhappened to Q507.JZOn Sat, Sep 23, 2023 at 8:37?PM Cliff <ae5zaham@...> wrote:
Hi John,
Well to pick up the thread we had earlier, I got a new Q507 and installed it.
Tested the modulator for being on based on what Hans said about the fact that before the first transmission the drain shows high, then shuts the modulator off after the first transmission. It does exactly that so apparently the modulator is fine, i.e. not on as we thought, at at least.
Now the gate is 11v before the first transmission then 0.3 after transmission. Maybe the Q507 was bad after all?
Anyway it's working again. Wonder how long the finals will last this time. Hmmm....
Hopefully it's fixed now, but I won't know until I use it for a while.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:48, Cliff <ae5zaham@...> wrote:
John,
Thanks for the explanation. I fully understand. No controversy here.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:40, John Z <jdzbrozek@...> wrote:
Cliff,
Sorry to hear about the busted FET!
The modulator in QMX serves a number of special functions that QDX does not require.
CW wave shaping, to eliminate annoying ?transmitted key clicks, is one example.
Someday it will be used to create. synthetic SSB.
Hans also uses it to gracefully wind down the transmit power at the end of each transmission. That should avoid a damaging Ldi/dt spike from the PA's power feed inductor.
QDX does not benefit from that spike protection, as it has no modulator circuit. Hence, you will see discussions about the use of commutating diodes, zener diodes, or other means to protect the QDX finals.
These discussions always seem to drag along some controversy. There should be none. The Ldi/dt spike is real and it puts the PA transistors into a dangerous out-of-spec condition.
JZ KJ4A
On Tue, Sep 19, 2023, 2:14 PM Cliff <ae5zaham@...> wrote:
John,
Looking at the schematic for the QDX there is no modulator like the QMX and the L14 which is similar to the L507 in function is always at the input voltage, 11V in this case. At least in the QDX it's normal to have the input voltage on that coil all the time, but I guess not in the QMX.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 11:34, Cliff <ae5zaham@...> wrote:
Thanks John,
Well, the gate had 6.5V on it. The Source and Drain had 11V. Wasn't sure whether that was 6.5 was high or low. Low I was expecting to be 0V. I lifted the Gate pin and now the pad for the gate is still 6 V, but the Drain is 5.4 and the Source is still 11V. It appears as if Q507 was being turned on. Interesting with the gate disconnected from the pad the idle current drain still hasn't dropped. Seems as if that wasn't causing an increase in receive current.
What do you think?
73,
Cliff, AE5ZA
On Sep 19, 2023, at 00:07, John Z <jdzbrozek@...> wrote:
Cliff,
You have confirmed that there is a problem at the PMOSFET modulator.
When all the BS170 are good, they are all off in receive mode and you can expect a normal receive current level even if the modulator is stuck "on". When one or more have failed, a stuck modulator will allow elevated receive current.
Your reading of 11 volts during receive is proof that the modulator is turned on, wrongly.
The next step is to measure the gate voltage at Q507 in receive. If it is low, Q507 is being driven on by the four 'difference amplifier' transistors that compare the DAC signal from the processor to the output of the modulator and produce the gate drive signal for Q507. Determining which have failed would be the next challenge.
If the gate voltage us high, and Q507 is conducting, Q507 is shorted.
...
I see a preceding post that goes on a remarkable run-on over your use of sockets. There is a grain of truth in there, amongst several misconceptions, in that socketing does somewhat impede heat flow out the leads of the BS170. That was neither your initial problem nor your biggest problem now.
In the future I would advise a thin layer of thermal compound under the transistors, and between them and the washer. too. Do not over tighten the nut and screw as thermally expanding transistors will be squeezed badly.
The molded case of modern TO-92 transistors contains a thermally conductive filler to allow the case to participate in heat rejection. The via holes that pepper the plated pad that the transistors sit upon are not helping that at all. They impart surface irregularities ( and hence air gaps) that get in the way of good heat rejection. A little thermal compound helps overcome that.
Good luck, JZ KJ4A
On Mon, Sep 18, 2023, 11:14 PM Cliff <ae5zaham@...> wrote:
Good thoughts JZ.
When I see the idle current go up I open things up and find one of the BS170s is causing it. Pull the bad one and it goes back to normal receive (idle) current so I doubt that the modulator is on, but will verify it anyway.
In receive has 11V on it. Does that mean that Q507 is bad? Sorry I'm not familiar with how Mosfets work? Could the very bad current draw when I had left off the antenna caused that? That looks like a pain to remove without a hot air rework system which I don't have.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 21:05, John Z <jdzbrozek@...> wrote:
Cliff,
I think you are correct when you suggest that something more is going on with the rig.
I suspect that the PMOSFET modulator may be stuck "on". It would not afford protection against destructive Ldi/dt spikes from L502 if it were stuck.
You mention idle current going up when BS170s fail. I presume that you mean current drawn while in receive. That would be another indication of a fault in the modulator section. The modulator should take PA current to zero in receive.
If you see voltage on L502 during receive, that would confirm a stuck modulator.
You might be able to go further in diagnosis using just a multimeter, but at that point it may be better to send your QMX to Jeffrey W. Moore for repair.
JZ KJ4A
On Mon, Sep 18, 2023, 8:46 PM Cliff <ae5zaham@...> wrote:
Hi Paul,
Thanks for the response.
I've had it fail while in different modes. Olivia usually has the longest key down times since it's quite slow. This last time I was in Feld Hell which is one of the easiest modes there are on the rig. It's not a constant transmission, but many with very short pauses mixed in. The rig had been sitting for several hours so it wasn't even hot.
No scope here, sad to say. Testing the Q503 with digital VM and verified 2.5 volts on all final gates.
You raise an interesting point about spikes. Maybe the first time it was damaged was bad enough that it damaged something so there are spikes that are damaging the finals. What that would be I don't know, but maybe one of the experts on this list may have an idea.
Power and SWR are the same on a dummy load. Could try simulating a QSO with the dummy load, but it might take a long time to get enough time on the rig to act up.
The Power/SWR Meter is built into the dummy load and is in between the tuner and the rig so I take it the SWR is what the rig sees. Putting the SWR meter after the tuner shows 1.3:1 SWR. Tuning with the LED indicator in tune mode ends up with the same settings on the tuner and the current draw is the same so I assume power out is the same also.
I agree, something I/we don't understand is going on.
As it is now I'm getting reticent to use the QMX as it's unreliable these days. I have 2 QDX rigs I could use, but prefer the QMX if it can be made reliable by figuring out what is wrong. Of course future firmware upgrades should make it even better.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 18:04, Paul - AI7JR <paul.hanchett@...> wrote:
You mentioned Olivia-- Is that the predominate mode here? Were there other modes where you had a problem? You mention 8-10 minute key-downs, is that typical of your operations?
Are you able to confirm proper waveforms on the gates and drains of the BS170's? No spikes, proper voltages?
Could you simulate a QSO into a dummy load, do the currents look the same? You mention the SWR is 1.0, is the load impedance presented to the QMX actually 50 ohms, or something else? (Could it be that the output impedance of the QMX isn't really 50 ohms --likely, really-- and when we adjust for 1:1 SWR, maybe the antenna isn't being adjusted to be 50 ohms?)
Your experience suggests to me that we don't understand everything about what's going on!
Paul -- AI7JR
On 9/18/23 14:53, Cliff wrote:
I built this QMX within a a month of the release of the kit. It worked great for 2 1/2 months or so. Solid even with long key down modes of 8 to 10 minutes. Power out about 4 watts.? Then I unknowingly left the antenna disconnected and called CQ 3 or 4 times in Olivia mode. I happened to look at the Buck/Boost Converter and noticed it was in current limiting mode so immediately shut off the power. Damage done. <Sigh .....>
I installed sockets for the finals and replaced all 4 BS170s and the driver IC503. Worked fine for an hour or maybe 2, btw SWR is 1.0 with a manual tuner. Then, with the antenna attached, it again blew a final during a QSO and showed current limiting. Replaced the bad BS170 and all seemed fine. IC503 looked good. This scenario ?has repeated a number of times now. Replace the bad BS170, check IC503 and it'll run fine for an hour or two of QSOs. I even replaced IC503 and all the finals again just to be sure all was ok.
I've also seen twice where the idle current increased from 130 to 200 ma. That was an indicator of a bad BS170 also.
I'm being forced to conclude that there is something else going on besides the finals just dying because of operator error. All parts are from Mouser so quality should be good. Power out is still about 4 - 4.2 watts. Current is about 750 ma, sometimes nearly 800ma (the increase puzzles me) and voltage is 11.0 volts. SWR is 1.0.
No physical shorts that I can see. It's also not always the same BS170 position that goes bad. The time before last it was Q505 and just now it was Q504.
I sure hope someone has an idea of what can be going on. I've been running out of the case to be sure it wasn't heat build up.
Any and all suggestions welcome.
Thanks.
73,
Cliff, AE5ZA
|
And I apologize for misspelling toroid. It's been a long week.
-Alex AD5MO
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Re: QMX RF power line diode switches
Ryuji,
You are a fearless experimenter! Kudos, OM!
73 KJ4A?
On Mon, Sep 25, 2023, 2:26 PM Ryuji Suzuki AB1WX < ab1wx@...> wrote: Rich Evan thanks for the pointers. I¡¯ll have to research the past archive from my desk later
I was trying to see the safe limit if the output power the other day by increasing the powe and supply voltage. Around 12V supply I got 10W output. A bit above the finals blew and I was doing the postmortem analysis. The final transistors should be able to push more power easily and I was thinking of a possibility of what went wrong. I suspect the diodes of the ¡°off¡± LPF branches conducted and the RF current went straight to the ground. 10w on 50 ohm is about 25v rms so that may be the problem.
So using LDMOS and 1:1 output transformer there¡¯s great amplifier reserve capacity but the danger line is also right there.
It¡¯s a bit of heavy duty soldering work to replace the finals but I¡¯d rather know the limits before I take it to the field. I¡¯ll need a supply voltage limiter once I find out a good supply voltage with enough safety margin. The burnt chip smelled bad and the drain contact that I soldered looked like spot welded - I couldn¡¯t unsolder it.
|
Re: QMX RF power line diode switches
Rich Evan thanks for the pointers. I¡¯ll have to research the past archive from my desk later
I was trying to see the safe limit if the output power the other day by increasing the powe and supply voltage. Around 12V supply I got 10W output. A bit above the finals blew and I was doing the postmortem analysis. The final transistors should be able to push more power easily and I was thinking of a possibility of what went wrong. I suspect the diodes of the ¡°off¡± LPF branches conducted and the RF current went straight to the ground. 10w on 50 ohm is about 25v rms so that may be the problem.
So using LDMOS and 1:1 output transformer there¡¯s great amplifier reserve capacity but the danger line is also right there.
It¡¯s a bit of heavy duty soldering work to replace the finals but I¡¯d rather know the limits before I take it to the field. I¡¯ll need a supply voltage limiter once I find out a good supply voltage with enough safety margin. The burnt chip smelled bad and the drain contact that I soldered looked like spot welded - I couldn¡¯t unsolder it.
|
Re: QMX RF power line diode switches
Ryuji, Evan is correct. The clever voltage doubling reverse bias circuit should prevent that from ever being a problem.
The 1N4007 achieves its high reverse breakdown rating by being a true PIN structure. It just happens to be sold in a PTH leaded package for a very low price. We hams can be grateful for small favors!
A "true" PIN diode would also need strong smart reverse bias. The old saying TINSTAAFL applies here.
JZ
On Mon, Sep 25, 2023, 12:38 PM Evan Hand < elhandjr@...> wrote: Hi Ryuji,
Hans had posted how he came about using the 1n4007 as a PIN diode for the LPF switches.? You bring up one point that he found that there needs to be higher than the peak plus diode drop to ensure the diode does not conduct.? That is why there is a voltage doubler.? The voltage is used to keep the non-selected diodes off.? A failure of that circuit could cause the issue.? To the best of my knowledge, none have been reported.
Others may have more information and the link to the post that describes his investigation into using the 1n4007.
73
Evan
AC9TU
|
Cliff, darn, sorry to hear that!
Did you note which BS170 blew? Was it same or different from last time? I presume you checked SWR and it was OK? What current draw were you seeing from the PS in xmit?
Your failure sounds like it could be heat related.? Do you use thermal compound under the BS170s? IIRC you socketed the PA transistors.
Is anything else in the box dumping too much heat?
When you reassembled the washer, nut and screw that hold down on the PA transistors, did you leave the nut just finger tight, or did you torque down on it? Are there any stress concentrating irregularities on the PCB surface under the PA transistors? Has the case of the failed transistor cracked?
Yes, many questions...
JZ
Hi John,
Well, I hoped it was fixed, but apparently not.?
Just blew at least one BS170. Had it all assembled, but outside the case. Worked for about and hour of transmit time, most of that on FT8. It was happily working a station when the current draw went up to max current limiting. Powered down and pulled the finals and all is fine current wise. Verified drive voltages on the gates - all 2.5V in TX and zero on RX.
Q507 still checks good.
This is getting frustrating.? Of course I blame myself for so stressing the rig the first time it blew a final by not noticing the high current draw for a while. The question in my mind is whether the stress damaged something or what ever caused the first one blown BS170 is the issue.? Would still like to fix it though, but can't forever keep throwing BS170s at it either.
Don't feel like it's your responsibility to find the issue, but I do very much appreciate your insights into the circuits and suggestions.
OK Cliff!I'm glad you have it working. I just wish we knew exactly what hadhappened to Q507.JZOn Sat, Sep 23, 2023 at 8:37?PM Cliff <ae5zaham@...> wrote:
Hi John,
Well to pick up the thread we had earlier, I got a new Q507 and installed it.
Tested the modulator for being on based on what Hans said about the fact that before the first transmission the drain shows high, then shuts the modulator off after the first transmission. It does exactly that so apparently the modulator is fine, i.e. not on as we thought, at at least.
Now the gate is 11v before the first transmission then 0.3 after transmission. Maybe the Q507 was bad after all?
Anyway it's working again. Wonder how long the finals will last this time. Hmmm....
Hopefully it's fixed now, but I won't know until I use it for a while.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:48, Cliff <ae5zaham@...> wrote:
John,
Thanks for the explanation. I fully understand. No controversy here.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 14:40, John Z <jdzbrozek@...> wrote:
Cliff,
Sorry to hear about the busted FET!
The modulator in QMX serves a number of special functions that QDX does not require.
CW wave shaping, to eliminate annoying ?transmitted key clicks, is one example.
Someday it will be used to create. synthetic SSB.
Hans also uses it to gracefully wind down the transmit power at the end of each transmission. That should avoid a damaging Ldi/dt spike from the PA's power feed inductor.
QDX does not benefit from that spike protection, as it has no modulator circuit. Hence, you will see discussions about the use of commutating diodes, zener diodes, or other means to protect the QDX finals.
These discussions always seem to drag along some controversy. There should be none. The Ldi/dt spike is real and it puts the PA transistors into a dangerous out-of-spec condition.
JZ KJ4A
On Tue, Sep 19, 2023, 2:14 PM Cliff <ae5zaham@...> wrote:
John,
Looking at the schematic for the QDX there is no modulator like the QMX and the L14 which is similar to the L507 in function is always at the input voltage, 11V in this case. At least in the QDX it's normal to have the input voltage on that coil all the time, but I guess not in the QMX.
73,
Cliff, AE5ZA
On Sep 19, 2023, at 11:34, Cliff <ae5zaham@...> wrote:
Thanks John,
Well, the gate had 6.5V on it. The Source and Drain had 11V. Wasn't sure whether that was 6.5 was high or low. Low I was expecting to be 0V. I lifted the Gate pin and now the pad for the gate is still 6 V, but the Drain is 5.4 and the Source is still 11V. It appears as if Q507 was being turned on. Interesting with the gate disconnected from the pad the idle current drain still hasn't dropped. Seems as if that wasn't causing an increase in receive current.
What do you think?
73,
Cliff, AE5ZA
On Sep 19, 2023, at 00:07, John Z <jdzbrozek@...> wrote:
Cliff,
You have confirmed that there is a problem at the PMOSFET modulator.
When all the BS170 are good, they are all off in receive mode and you can expect a normal receive current level even if the modulator is stuck "on". When one or more have failed, a stuck modulator will allow elevated receive current.
Your reading of 11 volts during receive is proof that the modulator is turned on, wrongly.
The next step is to measure the gate voltage at Q507 in receive. If it is low, Q507 is being driven on by the four 'difference amplifier' transistors that compare the DAC signal from the processor to the output of the modulator and produce the gate drive signal for Q507. Determining which have failed would be the next challenge.
If the gate voltage us high, and Q507 is conducting, Q507 is shorted.
...
I see a preceding post that goes on a remarkable run-on over your use of sockets. There is a grain of truth in there, amongst several misconceptions, in that socketing does somewhat impede heat flow out the leads of the BS170. That was neither your initial problem nor your biggest problem now.
In the future I would advise a thin layer of thermal compound under the transistors, and between them and the washer. too. Do not over tighten the nut and screw as thermally expanding transistors will be squeezed badly.
The molded case of modern TO-92 transistors contains a thermally conductive filler to allow the case to participate in heat rejection. The via holes that pepper the plated pad that the transistors sit upon are not helping that at all. They impart surface irregularities ( and hence air gaps) that get in the way of good heat rejection. A little thermal compound helps overcome that.
Good luck, JZ KJ4A
On Mon, Sep 18, 2023, 11:14 PM Cliff <ae5zaham@...> wrote:
Good thoughts JZ.
When I see the idle current go up I open things up and find one of the BS170s is causing it. Pull the bad one and it goes back to normal receive (idle) current so I doubt that the modulator is on, but will verify it anyway.
In receive has 11V on it. Does that mean that Q507 is bad? Sorry I'm not familiar with how Mosfets work? Could the very bad current draw when I had left off the antenna caused that? That looks like a pain to remove without a hot air rework system which I don't have.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 21:05, John Z <jdzbrozek@...> wrote:
Cliff,
I think you are correct when you suggest that something more is going on with the rig.
I suspect that the PMOSFET modulator may be stuck "on". It would not afford protection against destructive Ldi/dt spikes from L502 if it were stuck.
You mention idle current going up when BS170s fail. I presume that you mean current drawn while in receive. That would be another indication of a fault in the modulator section. The modulator should take PA current to zero in receive.
If you see voltage on L502 during receive, that would confirm a stuck modulator.
You might be able to go further in diagnosis using just a multimeter, but at that point it may be better to send your QMX to Jeffrey W. Moore for repair.
JZ KJ4A
On Mon, Sep 18, 2023, 8:46 PM Cliff <ae5zaham@...> wrote:
Hi Paul,
Thanks for the response.
I've had it fail while in different modes. Olivia usually has the longest key down times since it's quite slow. This last time I was in Feld Hell which is one of the easiest modes there are on the rig. It's not a constant transmission, but many with very short pauses mixed in. The rig had been sitting for several hours so it wasn't even hot.
No scope here, sad to say. Testing the Q503 with digital VM and verified 2.5 volts on all final gates.
You raise an interesting point about spikes. Maybe the first time it was damaged was bad enough that it damaged something so there are spikes that are damaging the finals. What that would be I don't know, but maybe one of the experts on this list may have an idea.
Power and SWR are the same on a dummy load. Could try simulating a QSO with the dummy load, but it might take a long time to get enough time on the rig to act up.
The Power/SWR Meter is built into the dummy load and is in between the tuner and the rig so I take it the SWR is what the rig sees. Putting the SWR meter after the tuner shows 1.3:1 SWR. Tuning with the LED indicator in tune mode ends up with the same settings on the tuner and the current draw is the same so I assume power out is the same also.
I agree, something I/we don't understand is going on.
As it is now I'm getting reticent to use the QMX as it's unreliable these days. I have 2 QDX rigs I could use, but prefer the QMX if it can be made reliable by figuring out what is wrong. Of course future firmware upgrades should make it even better.
73,
Cliff, AE5ZA
On Sep 18, 2023, at 18:04, Paul - AI7JR <paul.hanchett@...> wrote:
You mentioned Olivia-- Is that the predominate mode here? Were there other modes where you had a problem? You mention 8-10 minute key-downs, is that typical of your operations?
Are you able to confirm proper waveforms on the gates and drains of the BS170's? No spikes, proper voltages?
Could you simulate a QSO into a dummy load, do the currents look the same? You mention the SWR is 1.0, is the load impedance presented to the QMX actually 50 ohms, or something else? (Could it be that the output impedance of the QMX isn't really 50 ohms --likely, really-- and when we adjust for 1:1 SWR, maybe the antenna isn't being adjusted to be 50 ohms?)
Your experience suggests to me that we don't understand everything about what's going on!
Paul -- AI7JR
On 9/18/23 14:53, Cliff wrote:
I built this QMX within a a month of the release of the kit. It worked great for 2 1/2 months or so. Solid even with long key down modes of 8 to 10 minutes. Power out about 4 watts.? Then I unknowingly left the antenna disconnected and called CQ 3 or 4 times in Olivia mode. I happened to look at the Buck/Boost Converter and noticed it was in current limiting mode so immediately shut off the power. Damage done. <Sigh .....>
I installed sockets for the finals and replaced all 4 BS170s and the driver IC503. Worked fine for an hour or maybe 2, btw SWR is 1.0 with a manual tuner. Then, with the antenna attached, it again blew a final during a QSO and showed current limiting. Replaced the bad BS170 and all seemed fine. IC503 looked good. This scenario ?has repeated a number of times now. Replace the bad BS170, check IC503 and it'll run fine for an hour or two of QSOs. I even replaced IC503 and all the finals again just to be sure all was ok.
I've also seen twice where the idle current increased from 130 to 200 ma. That was an indicator of a bad BS170 also.
I'm being forced to conclude that there is something else going on besides the finals just dying because of operator error. All parts are from Mouser so quality should be good. Power out is still about 4 - 4.2 watts. Current is about 750 ma, sometimes nearly 800ma (the increase puzzles me) and voltage is 11.0 volts. SWR is 1.0.
No physical shorts that I can see. It's also not always the same BS170 position that goes bad. The time before last it was Q505 and just now it was Q504.
I sure hope someone has an idea of what can be going on. I've been running out of the case to be sure it wasn't heat build up.
Any and all suggestions welcome.
Thanks.
73,
Cliff, AE5ZA
|
While at work, I was looking at a photo of the board on my phone I took before redoing the T1, an I just realized that the L12 inductor has a rather sizable slack on the last "turn", as in the wire going through the torroid isn't even touching the inside wall of the torroid. How I managed that is one big shoulder shrug. Obviously I'll fix it tomorrow evening when I can get my hands back on the work station, but pardon the ignorant query: could that be killing the RF out?
|
Hi all.
After initially testing a new QDX on all bands (with erratic RF sweep results), a newly built QDX (5/low band version) now thinks it is 80m only - has anyone ever seen this? I've tried a factory reset, but the serial menu only gives me one band - 80m, in both the tests and band configuration menu.?
A bit more info -
I build a new device, powered it up fine, however the RF Sweeps gave very strange results - but all bands were definitely available/tested. I powered it down and found a solder bridge. Made a note of it at the time, but lost it - from memory/looking at the underside of the board either R9 or C37 was bridged to a nearby inductor. I cleared this, checked everything else more carefully and powered back up into its present (mono-band) state.?
Any suggestions much appreciated.
Thanks in advance,
Dan
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Ryuji Suzuki AB1WX
Ted 2E0THH