Hmmm... I've never figured out how to access the QMX usb on my Mac. I read it can be done, but it's so easy to do on the Pi I've never messed with it on the Mac.
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Cliff,
You should put the radio into IQ mode and let Audacity process the incoming I and Q channels off of USB.
From what you said about your sweeps, you may already have the answer, though ;-(
The PCM1804 is quite likely damaged.
JZ John,
RF Sweeps and AF sweeps are pure garbage.?
No scope here.?
Using Raspberry Pi for testing.?
Regarding using Audacity just run audio output from the QMX into Audacity?
I thinking I'll just go ahead and order the IC. Looks very likely it's bad.
RF Sweep
AF Sweep
Roger that.
That check can be done but it is a bit complicated and only works if you can? actually hear signals.
First off, bad IF sweeps are a big clue. If one ADC channel has failed then IF sweeps will show no suppression of the unwanted sideband
If the sweeps are just noisy garbage, perhaps both ADC channels have failed.
Going deeper:
Tune in a constant carrier to produce an audio beat note near 700 Hz.
Using the oscilloscope, verify that clean sine waves exist at pin 1 of IC405 and IC406. The signals should be near 12KHz in frequency and 90 degrees out of phase. If so,? the entire RX chain ahead of the ADC is good.
Via the terminal program,? put the QMX in IQ mode and observe the I and Q channels via the PC Audacity audio app. You should see two channels of approximately equal signal amplitude. Otherwise, something is wrong.
JZ
Ok, no harm in trying.?
Before I order the part for the PS Board, is there a way to check if the PCM1804 is good. Save on shipping if I order both at the same time.
It can be done, Cliff. I successfully did one recently. Of course Jeff Moore is there to help!
JZ Ouch! That one looks like it's beyond me to change out. If it proves bad guess I'll give it a go, but ......
Cliff, yeah, I am also concerned that this is not the last layer of the onion that needs to be peeled down.
Overvoltage on the 5V supply rail tends to take out the PCM1804 ADC chip. Its analog front end runs on 5V, the digital portion on 3,3V. It is the weak link of all the devices that run on the 5V rail. That may be the source of the unstable readings you see with the "good" SMPS module.
Keeping fingers crossed...JZ Ok, thanks. I like Mouser an they ship for $5 and I get it next day as they are close to me. I'll look at Digikey.
If this fixes the PS board then I'm puzzled about what else is not right. Fluctuating 5V rail and won't shut down. Hopefully that is an easier fix. Q108 is pretty tiny. Fun to change it.
Ouch! Cliff, I think you found the culprit.? Digikey has the AO3415.
JZ Yes, Q108 is bad. Measurements 20 - 50 ohms.
Next question, looking at Mouser AO3415A doesn't come up. I get a PJ3415 to come up. Is there a better part number?
Agreed, Cliff. That looks OK. Try the same test on Q108. Let's see what we have there.
JZ John,
Drain-Source - Starts out at 10K then charges up to 22K+ (same regardless of +/- orientation, Gate-Drain 110K, Gate - Source 99K. Seems good to me. ?
Cliff , Remove the module from the main board. Locate Q106. Using an ohmmeter, check the resistance at Q106: gate-source, gate-drain, drain-source. All readings should be above 10K ohms. Any reading much less than that suggests a problem.
John,
How would I do that? Checking in circuit and comparing with the good and bad boards they seem very similar in all combinations of resistance measurements.
Duty cycle =0! That means the MCU is doing all it can to throttle back the 5V SMPS and is finding it has no control at all.
Possibly one or more damaged transistors on the 5V SMPS module.
I would check Q106 for shorts.
JZ Ludwig,
The QMX will not boot at 7V. 9V will let it boot so the screen shot if with 9V.
As it sits there the 5V varies up and dow a little. If I go to 10V in it varies up 5.8 or so. On May 29, 2024, at 15:59, DH8WN via ??< DH8WN@...> wrote:
Cliff,
it looks like a problem in the control loop.
How and where did you measure VCC?
If really 6 V and more D108 on board #1 must be broken or disconnected. But this isn't the reason for the high VCC. It's only a lack of protection.
Please show a screen shot of Terminal - Hardware tests - Diagnostics. But use only around 7 V input to protect the QMX. And what is VCC in this situation.
73, Ludwig
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