Re: QDX - protection of BS17O PA
On Wed, Sep 6, 2023 at 11:15 AM, Gary W9TD wrote:
At Motorola, we put a known SWR load on the end of a line stretcher and were
therefore able to test a PA over the entire fixed VSWR circle of the Smith
chart. This was easy to do at UHF, but would not be practical at HF.
A lot of LDMOS transistors are tested that way and the manufacturers very often claim no deterioration to the device with SWR > 65 or sometimes infinity at any phase angle. Their VDS,max and VGS,max are quite modest on spec so the safety margin is built-in outside of the specs...
I think a variable capacitor and a variable inductor would cover some portion of a "very high" SWR circle, but that may not be enough. A combination of quarter wavelength transmission line would flip the portion of the circle covered. Not having to use a rolling inductor (lossy!) is very useful here.
I don't think covering a constant SWR circle is as important here. It's a lot easier to build a circuit that travels on a circle that tangents on the unit circle at R=0 (shunt reactance) or R=infinity (series reactance).
I would
guess that many of the points around the Smith chart VSWR circle could be
generated by programmable impedances (LCR networks switched by relays).
It can be done by an antenna tuner of some kind... preferably ones that have widest match space. Then terminate the output terminal with 50ohm but then control the network to create arbitrary reflection coefficients.
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Re: #qmx Don¡¯t Use USB-C PD to power your QMX?!
#qmx
I have retrofitted my QMX smps 5v board with a 5A zener. It won't fit in the exisiting space surface mounted. I was able to run 2 small insulated wires up from the board's pads where the 5.6v 500mA zener was removed. Then soldered those to the 5A zener. By twisting the newly wired surface mount packaged zener 180 degrees with a tweezer, it sits nicely and out of the way just above where the original used to be. I put a dab of electronics silicone under it to keep it in place. I tested that smps module removed from the rest of the transceiver, and verified the new ZENER is keeping the voltage below 5.6V. I didn't stress it at all (current limited to only 50mA), though I could feel it get warm during my overvoltage tests. Thank you @Chris G5CTH for posting your smps test procedures /g/QRPLabs/message/106787 .
In my case, prior to upgrading that Zener from 500mA to 5A, my QMX main board wound up having shorts on VCC & VDD somewhere, so I ordered a new QMX kit rather than troubleshooting at this time. Jeff Moore indicated it could likely be repaired, but would be quite the PITA to locate the issues and replace components. I may defer that task to later this winter to see if I can revive it. I used that QMX for about a month every day while it was working, and it was working great right from day 1.
I killed my QMX (firmware 1_00_009) when I attempted to see how well it might operate with an old MFJ Mag Loop antenna I had ... While it was powered up and working fine in receive mode (using a PD battery and 12v negotiating usb adapter to power it, which is why I'm posting to this topic) and everything sitting atop a wooden folding TV tray (small table), I shifted my MS Surface PC a tad, which sent the QMX dangling off the end of this tiny table by the antenna, USB, and power cables. It didn't hit the floor, just dangled about a foot or so down from the edge of the table. It was screaming bloody murder; well not literally, but I sensed its fear as it dangled above the carpet below. Yes, we had become emotionally attached to each other; I loved my little QMX! 
I cringed as I went to grab it as I saw the screen go dark then, it lit up and rebooted, and may have done that twice before I stabilized it back on my tiny table. I knew this could be a fatal mishap.
Note to self: Tiny table == Bad idea.
It booted up, but receive was only loud static noise.
Fast forward, and I've got it apart hoping that 5.6 Zener took one for the team. I want to test that Zener off the board (because on board I was just seeing a short), and my fumbling with a spring clip while attempting a test of it sent that little spec of pepper flying, never to be seen again. So I'll never know if that Zener was good, shorted, or open.
A couple of emails later with Jeff Moore, he dropped the bad news on me. The QMX main board had shorts on both the 3.3V and 5V rails somewhere (based on tests he asked me to provide results of). So the Zener didn't protect the radio from that abuse (though I wish I had that particular Zener to test if it indeed failed).
Definitely operator error on my part since I already knew of the potential input voltage jump issue, and I have no way of knowing what input voltage the QMX experienced during its short free-fall and the tug, oh that tug, on the power cord.
But I am now a bit concerned about running a QMX via a wall powered 12V power supply (which I use often). If I inadvertently cut power to the power supply before turning off the QMX, what voltages is the QMX dealing with? And what if there's a mains power failure while the QMX is on?
Hopefully a 5A 5.6V Zener will prevent this type of abuse from killing my next QMX; though I don't intend to test whether it works or not.
Hans, if you're needing an expert at subjecting real-world dumb & dumber abuse to a perfectly good QMX to see how it might fail, please send a few my way. I'll send them back to you perfectly abused so you can do a postmortem autopsy.  I'll have my tiny TV tray-table ready for the tests. I wonder if I can balance my mag-loop on an inner tube while floating around in the ocean?? The wheels are already turning; I'll be ready.
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Re: QDX - protection of BS17O PA
On Wed, Sep 6, 2023 at 06:38 AM, Chris wrote:
Is there anything worse than an open or shorted transmission line? Both
reflect all the power back to the transmitter (ignoring losses) and what you
get back depends on the electrical length of the line and the frequency.
The condition that makes perfect reflection of power is infinitely many. If you think of a Smith chart. Any point on the unit circle (that includes R=0 and R=infinity) will satisfy that. In reality, we don't really see a load on that circle, but we often see load just inside that circle. Amateurs often call it high SWR without specifying what the actual complex impedance is.
A practical example. If you have a low loss coax that is either open or short end, and the other end is attached to the transmitter. Depending on the length of the cable, the transmitter will see a near total reflection of power but neither short nor open.
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Re: QDX transmit troubleshooting advice¡
If I understand, the point of L14 is to limit current transients
as current switches from one side of the push-pull to the other.
This transition will happen at twice the operating frequency... I
think having current flowing in both sides of the output
transformer would be a Bad Thing, for many values of Bad!
Putting a resistor across L14, or adding a decoupling capacitor
from the center tap to ground, defeats L14's purpose, doesn't it?
Some people have put a diode across L14 to catch the turn-off
spike, but that reduces output power, suggesting it (the diode) is
doing more than just catching the spike when drive is removed
from the PA...
(Haven't heard how adding those 47 volt zeners affect operation.
If they keep the BS170's from blowing, even if they self-sacrifice
in the process-- I don't think they will, there's not that much
power in the spikes-- isn't that a net win?)
I also think mechanical stress on TO-92 can be a source of
unreliability.
Agree, and would probably show as a thermal problem.
Paul -- AI7JR
On 9/18/23 21:29, Ryuji Suzuki AB1WX
wrote:
toggle quoted message
Show quoted text
I read the theory on the RF choke's flyback voltage blowing
MOSFETs with interest. I was interested in the efficacy and
potential penalty of having a Zener to protect from high VSWR
load, but anyway...
I am not sure what kind of inductance model was used for L14 in
simulation. It's an inductor on lossy #43 ferrite. Well, that
loss in magnetic circuit may have only a small impact on the
transient spike.
One thing to remember is that the drain impedance of these
transistors is very low, like on the order of 5 - 20 ohm
depending on the winding ratio of T1, supply voltage and the
output power squeezed out from the amp (just draw the load
line). So, L14 does not have to have a huge reactance at the
lowest operating frequency. Also, there is little penalty in
adding a parallel resistor to L14 as long as the R is well
larger than the drain impedance. Say R is 470 ohm or something,
and that value should be enough to keep the flyback voltage very
low, if that is indeed a problem (I'm not really sold on that
theory). Same thing can be done across the primary windings of
T1. In fact, resistors are often added to the output
transformers when using modern LDMOS transistors (to increase
stability).
I also think mechanical stress on TO-92 can be a source of
unreliability. I would prefer to use DFN or PLD-1.5W LDMOS
transistors mounted on the board. SOT-89 is ok, too. If I had no
choice other than TO-92, I would insert the transistors, with a
tiny amount of thermally conductive silicone adhesive between
the transistor and the copper, bolt the washer down carefully
and lightly, wait for the adhesive to fully cure, loosen the
bolt and solder the leads. However, replacing the transistors
will be a lot of work when they blow.
Simulating high voltage from poorly matched load is a bit
tricky. Hams use SWR routinely but that measure is totally
inadequate for this discussion. What matters is the magnitude
and angle of the return power. Short or open load is not exactly
the harshest condition. There is a combination of mag and angle,
or a point somewhere on the Smith chart that generates high
voltage on the drain but that depends a lot on what goes in
between.
Generally speaking, LDMOS is a lot tougher than bipolar or
regular MOSFET in this scenario.
Incidentally, I have a Youkits EK1A 5W transceiver, and I
thought blew the final. The kit came with a counterfeit 2SC2078
anyway, which I did not like. So I changed it with real Sanyo
chip pulled from a junk CB rig but still didn't put out any
power. So I did a bit of troubleshooting and quickly found out
that the Zener diode for high SWR protection failed in short
mode, and that burnt the tiny pathetic RFC winding. I removed
the failed Zener, wound a real RFC on a stack of four FB43-101's
with 28 AWG wire (3t) and it pushed out 40dBm! I was driving a
counterfeit CB final transistor at double the rated power for
maybe 500 CW QSOs and I thought the transistor flied, but it was
the stupid Zener (looks like 3W-rated based on the size, about
5mm long and 2.5mm diameter) and RFC. I thought to do some
research whether to put in a 5W Zener or leave it out, and found
this thread.
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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?
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.
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? 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.
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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Re: How to get output to tracking page
#u4b
Anyone can give me some pointers on what I am doing wrong?
73 Stewart
ZR6WT
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Re: QDX transmit troubleshooting advice¡
I read the theory on the RF choke's flyback voltage blowing MOSFETs with interest. I was interested in the efficacy and potential penalty of having a Zener to protect from high VSWR load, but anyway...
I am not sure what kind of inductance model was used for L14 in simulation. It's an inductor on lossy #43 ferrite. Well, that loss in magnetic circuit may have only a small impact on the transient spike.
One thing to remember is that the drain impedance of these transistors is very low, like on the order of 5 - 20 ohm depending on the winding ratio of T1, supply voltage and the output power squeezed out from the amp (just draw the load line). So, L14 does not have to have a huge reactance at the lowest operating frequency. Also, there is little penalty in adding a parallel resistor to L14 as long as the R is well larger than the drain impedance. Say R is 470 ohm or something, and that value should be enough to keep the flyback voltage very low, if that is indeed a problem (I'm not really sold on that theory). Same thing can be done across the primary windings of T1. In fact, resistors are often added to the output transformers when using modern LDMOS transistors (to increase stability).
I also think mechanical stress on TO-92 can be a source of unreliability. I would prefer to use DFN or PLD-1.5W LDMOS transistors mounted on the board. SOT-89 is ok, too. If I had no choice other than TO-92, I would insert the transistors, with a tiny amount of thermally conductive silicone adhesive between the transistor and the copper, bolt the washer down carefully and lightly, wait for the adhesive to fully cure, loosen the bolt and solder the leads. However, replacing the transistors will be a lot of work when they blow.
Simulating high voltage from poorly matched load is a bit tricky. Hams use SWR routinely but that measure is totally inadequate for this discussion. What matters is the magnitude and angle of the return power. Short or open load is not exactly the harshest condition. There is a combination of mag and angle, or a point somewhere on the Smith chart that generates high voltage on the drain but that depends a lot on what goes in between.
Generally speaking, LDMOS is a lot tougher than bipolar or regular MOSFET in this scenario.
Incidentally, I have a Youkits EK1A 5W transceiver, and I thought blew the final. The kit came with a counterfeit 2SC2078 anyway, which I did not like. So I changed it with real Sanyo chip pulled from a junk CB rig but still didn't put out any power. So I did a bit of troubleshooting and quickly found out that the Zener diode for high SWR protection failed in short mode, and that burnt the tiny pathetic RFC winding. I removed the failed Zener, wound a real RFC on a stack of four FB43-101's with 28 AWG wire (3t) and it pushed out 40dBm! I was driving a counterfeit CB final transistor at double the rated power for maybe 500 CW QSOs and I thought the transistor flied, but it was the stupid Zener (looks like 3W-rated based on the size, about 5mm long and 2.5mm diameter) and RFC. I thought to do some research whether to put in a 5W Zener or leave it out, and found this thread.
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Re: QMX new build - power output
That's great news John. Getting 4W at 12V seems to be standard/usual for the QMX. I wouldn't go to the lengths of rewinding the LPF toroids for a fraction of a dB, as trat's unnoticeable in a QSO. I hope you'll enjoy your new toy as much as I am HI
72/73 de Enzo M0KTZ
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Reverse Beacon Network site down?
Hi,
It looks like?
isn't working at the moment. The telnet connection still is, but not the web page.
Does anyone know what might have happened?
72 de KD0FNR Hamilton
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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.
toggle quoted message
Show quoted text
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? 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.
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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Re: Circuit board and mounting hole dimensions.
#clock
Yeah I expected them to be in metric, too.? Some of your patriot customers can handle that sort of thing, hihi.? For the record, to prototype three copies of the design I'm working on, 9 bucks and change, shipped.? 80x37mm, hole spacing is 2.5mm up/down, 3.35mm right/left from the corners.?
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What follows is largely opinion, though I have done QC work on many hundreds of PC boards for the military-industrial complex.? At best, informed opinion, because I don't have a thermal camera to support or disprove what I'm saying.? Other opinions are very welcome!? Especially if someone has a modern thermal camera that can measure temperature in a small localized area, to measure lead temperatures with good solder joints, bad solder joints, socketed transistors.? (I also want a pony and a flying car...)
BS170s shed heat through their leads.? Normally the heat goes through a soldered joint to the board.? Does anybody think sockets provide better heat transfer than a soldered joint?
I'd be surprised.? Perhaps you're setting yourself up for failures.? And likely some additional parasitic capacitance.
I suggest you solder them in again.? If-and-when you need to replace them, cut the leads close to the board on all four transistors.? That makes it easy to remove the remnants of the leads, one at a time, carefully, gently, don't damage the board.? Drop in your next four transistors and solder them in.
I've been biting my tongue on one other observation -- I've seen some crappy solder joints in pictures of peoples' boards.? Insufficient solder on the component side.? IMO you need the barrel of the plated-through-hole filled with solder all the way from one side to the other, with a concave meniscus on both sides, to give the best heat transfer from the lead into the board.
About halfway down the page there's a beautiful example of a transistor with all three insufficient-solder joints.? It's the image with orange pushbuttons.
Dear, honored Hans -- I'm going to use you as an example.? Please forgive me.
Those BS170 joints show the same problem.
You're going to be making these solder joints from the non-component side of the board.? Adding some liquid flux at the BS170 lead and the pad -- on the component side -- will encourage solder to flow through the board better.? Use a little more dwell time with your soldering iron since the QMX board is multilayer and takes more heat to solder.? Reheat and touch it up on the component side if you have to.
I know there's no electrical connection on the component side of the board for any of the BS170s.? There's only the pads.? But we're not talking about electrical connection here, we're talking about getting good heat flow.
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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?
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.
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
|
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.
toggle quoted message
Show quoted text
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
|
I have a clock that uses WWVB for time sync and it almost always shows that it is connected here in Illinois.
Gary
W9TD
|
He did mention replacing IC503, several times...
On 9/18/23 16:40, ajparent1/kb1gmx
wrote:
toggle quoted message
Show quoted text
II'll bet IC503 s fried.??
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
|
II'll bet IC503 s fried.??
--
Allison
------------------
Post online only,?
direct email will go to a bit bucket.
|
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:
toggle quoted message
Show quoted text
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: Newbee Q: Are there 'designated builders' for QRPLabs kits?
You won't have to worry about SMD since those are already on the pcb. You do the through-hole stuff.
The Q103/Q104 short test is mandatory,
I had to use one of those china parts testers to id color coded parts since the china stripes all look the same! And I ain't color-blind!
Might be an idea to scoot the turns on the toroids for better power out since that is nearly impossible once they are on the board.
Scrape the windings ends in prep for soldering since heating does not really burn off the enamel.
Build from the most recent assembly instructions! I loaded mine and printed it and stuck it in a binder so I'd be all ready when the bag of parts got here! I had so much rework!
I apologize if you already knew all this!
--
73
Karl
KI4ZUQ
|
No, encoder pins are free of body.? It is just a faulty rotary encoder.? ?Hans offered to post me a new one if my Mouser replacement does not fit.
|
Ryuji Suzuki AB1WX
Paul - AI7JR
Stewart ZR1WT
Gary W9TD
Karl