Just found a scope about 1/2 an hour away. If I could get a list of points to check maybe I could find something helpful. Not sure what I'd use for a signal to trace though.
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Well John, add another mystery to the list, at least this one hopefully won't be so difficult to solve.
I'm happily going along decoding and sending CQ in Wsjtx and I noticed that all signals on the waterfall are gone. Totally empty, otherwise all is normal. Did all the usual, power offSigh, again!!
Verified the antenna connection is good all the way to the QMX by connecting to my other radio. That would hve been the easy solution. Then I notice that the Rx current draw is 15ma more than usual. Hmmm... I've seen when the rig is cold sometimes the Rx current is slightly lower than after the first Tx. Any, higher current is not a good sign, but maybe the fix will be easier anyway. I'm running the rig in Rx trying to see if I have a warmer IC or other component and so far all seem about the same. The CPU is the warmest chip on the board at the moment. Looks like a scope is needed, but as you know I don't have one or access to one. I don't like the idea, but I may need to send it to someone like Robert to diagnose.
No problem, Cliff!We still have a mystery on our hands, though. I hope we can get tounderstand the transistor failures!Perhaps run your radio at reduced power for a while?JZOn Tue, Sep 26, 2023 at 7:38?AM Cliff <ae5zaham@...> wrote:
John,
It was in CW mode. So sorry for the false alarm. It should make any difference, but I don't think I've mentioned I'm using firmware 006 since later versions don't do digi modes except the FT8 and it's ilk.
73,
Cliff, AE5ZA
On Sep 25, 2023, at 22:49, John Z <jdzbrozek@...> wrote:
Cliff,
If CLK0 and CLK1 are not presenting properly (same frequency, 90 degree phase shift between them), bad things could happen, such as greatly diminished receive sensitivity, spurious signals, etc. I wish you could scope them and demonstrate that they are OK. I am growing more suspicious that your MS5351 is malfunctioning and may be headed for a hard fail.
JZ
On Sep 25, 2023, at 10:49 PM, Cliff <ae5zaham@...> wrote:
Hi John,
Ok, well the clock generator is not constantly broke here if that is the issue so it's only a maybe. This is a needle in the haystack issue it seems.
Now a totally new issue has cropped up after installing a new BS170 in place of the bad one and put the radio ?back together outside the case.
Hooked it up and powered up and started Wsjtx. First off I noticed that the waterfall was very strange. There is a VERY strong signal from 500 hz to 900 hz on the waterfall. The rest of waterfall is pretty weak. It still decodes, but very weak signals. Changed bands and the same strong signal from 500 - 900 hz is still there and overall very weak receive. Fldigi also shows the signal and very weak receive. Something is majorly wrong. Hooked up my QDX and the band looks normal with lots of signals. I did not consciously do anything with the receive part of the circuit. I did push the turns down a bit on T507 to keep them from touching the bottom of the righthand encoder.
Did a factory reset just for good measure. TX power is normal for all bands.
Any idea where that 400 hz wide signal could come from?
Audio and RF sweeps all look good. Seems as if the issue is in the path from the antenna, but TX seems ok.
I've looked it over to see if anything is amiss and everything looks normal.
????
73,
Cliff, AE5ZA
On Sep 25, 2023, at 20:11, John Z <jdzbrozek@...> wrote:
Cliff,
Mooneers synth clock went to a hard fail after a power supply problem. It was easy to diagnose as a result. The clock outputs we¡¯re stuck low, the BS170 gates were stuck high.
I have seen a couple of instances on the forum where clock chips exhibited a heat related drop out. In QDX that would not be fatal to the PA. In QMX it would be because of a logic circuit difference.
JZ
On Sep 25, 2023, at 8:49 PM, Cliff <ae5zaham@...> wrote:
John,
Interesting thought. I suppose you are referring to IC204 (MS5353M). How did you diagnose the fault? Heat related would need somehow to heat it for testing without destroying it in the process.
Being on the bottom of the board it shouldn't get to hot, hopefully, but it is quite close to tQ506 if the heat percolated down through the board so maybe.
It's pretty tiny, not sure I could handle replacing that without a hot air rework station.
73,
Cliff, AE5ZA
On Sep 25, 2023, at 17:07, John Z <jdzbrozek@...> wrote:
Cliff,
If the clock generator chip should stall out with its outputs low while QMX is in transmit mode, the PA transistors will be turned hard on and at least one will fry. If you follow the clock signal through an XOR gate to the PA gates you will see this potential. Months ago I helped Mooneer diagnose this failure on his QMX and I only just now remembered.
Your problem may be a clock chip that gets hot and fades out, taking down the PA along the way.
JZ
On Sep 25, 2023, at 5:47 PM, Cliff <ae5zaham@...> wrote:
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.
73,
Cliff, AE5ZA
On Sep 25, 2023, at 14:31, John Z <jdzbrozek@...> wrote:
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
On Mon, Sep 25, 2023, 3:01 PM Cliff <ae5zaham@...> wrote:
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.
73,
Cliff, AE5ZA
On Sep 25, 2023, at 12:48, John Z <jdzbrozek@...> wrote:
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
On Mon, Sep 25, 2023, 1:26 PM Cliff <ae5zaham@...> wrote:
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.
73,
Cliff, AE5ZA
On Sep 23, 2023, at 19:44, John Z <jdzbrozek@...> wrote:
OK Cliff!
I'm glad you have it working. I just wish we knew exactly what had
happened to Q507.
JZ
On 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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