Hopefully changing out IC403 will clear the problem.?
Maybe the op amps have survived after all. They are spec'd to work up to a 36V supply voltage.
JZ
John, you're right. Inputs are low voltage, .9V on all 4.
Going back up the chain, IC403, inputs pins 7 & 9 2.5V, output pins 6, 10, 11 & 12 are 0.9V ???
Cliff , there is a chance the op amps have been fried.
They are very robust and it takes a lot to kill them. Yours would be the first I have seen reported here!? Congrats? ;-(??
Check the op amp inputs next, pins 3 and 5, both chips, 4 measurements in all. They too should be at 2.5VDC. If that looks good, then considering your reported results at the op amp outputs, the amps are probably toast.?
If those 4 measurements are not OK we may need to go further upstream in the RX chain.
JZ John,
Hmmm.... doesn't look good. Pins 1 & 7 about .6V. Vin, Pin 8 is 5V which should be good, but the outputs are way low. Blew them also you think?
Let's work back through the RX chain. What voltage do you measure on pins 1 and 7 of IC405 and IC406? You should see approximately 2.5V DC there.
JZ Well John, did that. New IC and no change. Exact same Audio and RF sweeps as last reported. Apparently something else in the path is toast or somehow my replacement process fries the chip. With the new #1 power board all is well and stable and the rig shuts off normally now.
Everything else seems to be working so it's a shame to be so close to "fixed" yet not there. No scope here to trace the signals.
Ideas?
Hmm, perhaps that's it, Cliff. Maybe it's time to try #2 PCM1804?
JZ John, I had touched up the connectors on the board just a few days ago and hadn't turn on the rig since. Some of them looked marginal so maybe that was what "fixed" it.
Cliff, check all the solder joints at SMPS connectors, both on the SMPS and on the main board. An erratic joint there especially if affecting SPMS voltage measurement by the MCU could explain a lot.
I would not recommend replacing the PCM1804 again just yet. Get closure on the root cause of that weird behavior first.
JZ Thanks for the reply John.
I'll take your questions/conclusions in order.
1. I agree, but tough to track down. See item #3.
2. That would make the whole board toast. Sigh! See item #3
3. This is VERY weird. This whole time it has rebooted when trying to shut down. The first time I did as you suggested the voltage went to nearly zero then come back up to 3.3v as it always has done. Tried it again and ???? it shutdown normally. Tried a number of times since and it shuts down normally now. What in the world is going on?
Referring to item #1 now the current drain is normal, about 130 ma compared to 120 ma on my normal QMX. What's going on here??? Also the fluxuations caused you to reply about the MCU are much less now, look pretty normal to me.
4. If the above all continue then it might be worth replacing the PCM1804 again.
I was about to say the whole board was toast, time to put it on a shelf, but now?maybe?it's fixable? What do you think?
Idle current 50 mA greater than with a good unit is definitely not OK. You very likely still have a busted chip somewhere in that radio.
Phantom fluctuation of reported Vcc ( point 1) is also bad news. It suggests that an ADC input at the MCU may be damaged.?
Can't shut down ( point 2). What happens to PWR_HOLD when you press and release the left encoder?
Sweeps still bad. PCM1804? ( point 3). It is possible that your replaced component has already been damaged.
JZ John,
Ok. Have compared with my good QMX and so far Q202 and components around it all check good. Voltages at different points agree also. I don't know an easy way to verify Q202 is good, but if the rig powers up I would think it would have to be working, yes?
Measuring the Pin90 connection to R209 seems good.
I've noticed that the idle current in the broken QMX is about 50ma more than it is in my good one. Don't know if that means anything or not.
Thanks again for all your help to figure this thing out. I really hate to give up on it, but I'm not sure where to go from here.
Known issues:
1. VCC fluxuating +/- .3V - only visable in the Hardware Diagnostic screen. On a VDM it is constant 5 Volts.
2. Can't shutdown via pressing the left encoder. It tries and then reboots.
3. Audio & RF sweeps are terrible and no receive using an antenna. Already replaced the ADC. Replacement ADC bad?
I suppose it is possible that a fault of some kind at Q202 or at pin 90 of the MCU could be creating a false power-on command.
JZ Yes, Cliff.?
That behavior violates my understanding of how the microcontroller executes a shutdown after detecting a push of the left encoder. The? PWR_HOLD? signal at the gate of Q104 should drop low after a very brief delay. Once it drops a spontaneous reboot should not be possible unless the left encoder is pressed again.
JZ
John,
Thanks for letting me know. Does that also apply to the not being able to shutdown via the left encoder button? Seems to me something is open that shouldn't be, but I'm not sure where to look. It tries to shutdown, but something is holding the voltage up long enough to cause a reboot.
Cliff,
Sorry, I am out of ideas on this one.? It's a pretty tough case, with behaviors I have not seen before and can't explain.
JZ John,
I really appreciate your help so far. Can I ask for more?
I finally gave up on the PS#1 board and ordered a new one.
Now I'm trying to fix the audio stream and the "can't power off" issue.
Re: audio stream.
I've changed PCM1804. A bit of a challenge, but not too bad. Same bad audio and RF sweeps. Where next should I look?
Re: Can't power off with the left encoder press. It tries then powers back up.
Powering off the rig with turning off the power supply works for sure, but if I switch the external power supply back on too quickly the QMX powers up again. I can see the voltage slowly decay when turning the power off the external power supply. Something isn't drawing the voltage down as quickly as it should. On my good QMX the voltage drains off very quickly. On this one it takes maybe 5 seconds to get down to zero voltage. Suggestions how to track that down?
No shorts I can see. I'm starting to feel this is getting out of my abilities. Probably should have ordered new boards in the first place. We still have the ADC issue and what ever is causing the power off to not work. Maybe not enough drain to empty the C107 fast enough?
Maybe tomorrow I'll try that test proceedure.
Thanks for all your efforts and time. Tomorrow will be another day.
Cliff, if you are powering the radio at 9V and the 5V supply is putting out 8.3V, either the 5V SMPS is stuck at 100% duty cycle, or there is a short circuit around the new Q108 you put in. Also, at that output voltage the Zener diode on the 5V board should be smoking hot.
I suggest you pull out that 5V SMPS and put it through the offline bench test procedure that has been posted here. Something is still very broken.
JZ John etc.,
Changed Q108 and now it won't boot and VCC is 8.3V. Ideas? On May 30, 2024, at 20:39, Daniel Walter via ??< nm3a@...> wrote:
Cliff,
After removing the ADC chip, check your voltages. If they are still unstable, you should find the cause before replacing the chip.?
--?
73, Dan? NM3A
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