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Re: Strange PCM3060 Failure Mode

PostPosted: Wed Jun 24, 2015 8:19 pm
by k1qn
I finally got the freeze spray, and it had no effect on the rig. When the power drifts down, it isn't changed when I hit the chips - one at a time - with the spray.

I also prod the contacts with a toothpick, to no avail.

The only thing that fixes it - and it always works - is to remove the DC power for an instant, then turn it back on.

The next diagnostic step is to reboot the computer to see if that has any impact.

I know problems this perplexing only happen to me. :-(

Re: Strange PCM3060 Failure Mode

PostPosted: Wed Jun 24, 2015 8:43 pm
by n9seo
k1qn wrote:Nope!


Next question: Is is possible to remove the PCM3060 without a heat gun?



I've done something like this (very very gently). https://www.youtube.com/watch?v=dCUSwADP6DE

Should give you an idea...Tho I would highly recommend a heatgun but do understand some times we have to improvise.

73 Kayne

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 1:14 am
by mrwizardly
Not without a lot of damage to clean up afterword.
From my brother that used to have to remove these types of parts (ICs) get a real narrow set of snipers and cut the legs off. Then suck off the left over legs with a vacuum soldering station.
However, that chip has some very close leads that you cannot get snipers in between the legs.
Heat gun is just about the only method.
Mark

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 12:44 pm
by kz1x
k1qn wrote:I finally got the freeze spray, and it had no effect on the rig. When the power drifts down, it isn't changed when I hit the chips - one at a time - with the spray.

I also prod the contacts with a toothpick, to no avail.

The only thing that fixes it - and it always works - is to remove the DC power for an instant, then turn it back on.

The next diagnostic step is to reboot the computer to see if that has any impact.

I know problems this perplexing only happen to me. :-(



Which chips did you hit with the spray?

The idea that a momentary DC interruption causes the problem to go away seems to indicate a low frequency oscillation of the voltage regulator. That could easily happen after a period of time, and would have to re-cycle when DC was dropped. I know you watched that voltage already, but, with a 'scope? Or a DMM?

It's easy for me to recommend swapping parts out since I have a hot air pencil! But low cost chips such as U8 and U14 could be changed out as either of them could cause this same symptom also.

I agree, rather puzzling. The fact that it works then doesn't seems thermal, but, the DC reset is a giveaway.

One more thing: what are the current levels in the various modes? I am fully aware that these are controversial readings (examine historical threads on this forum to see that) but within a comparative range they can still be revealing.

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 12:56 pm
by k1qn
I hit the PCM3060, then the PSOC, then each of the voltage regulators with the spray. ... eventually, the entire board got hit ...

By low frequency, what frequency range are you thinking of? I'm measuring the 3 regulated voltages (5v 5(b), and 3.3), and they're staying right at 5.030, 5.030, and 3.300. I can also make a measurement of input current by measuring the voltage drop across R1. (I spent time as a college EE lab instructor.) IIRC, the current on the 12 volt DC line dropped when the power dropped off - due to the reduced draw from the power amp. ... obviously. I didn't make any current measurements on the regulated power lines.

I don't have a scope, but I'm looking into "sound card scope software". Limited budget!

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 1:16 pm
by kz1x
I am thinking the oscillation frequency of your power change. Sub Hertz, maybe.

You may be able to do this sort of diagnosis work without a 'scope but that's like driving a car with the windows fogged over. You gotta go real slow and you aren't ever sure what you just hit.

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 1:20 pm
by k1qn
If the DC were changing that slowly, I'd see it drop on a DC meter. What I'd really like to see is the audio waveform coming out of the PCM3060. Is it clipping? Changing frequency?

Re: Strange PCM3060 Failure Mode

PostPosted: Thu Jun 25, 2015 9:33 pm
by k1qn
The attachment shows a trace of the "hot" side of R20 when it's at 50% power. The hot sides of R17-19 show the same things. These are the 4 outputs of the PCM3060. You can see it's trying to form a sine wave, but it's chopped off for .75msec every 1msec. Next question: what happens at 1kHz on the board?

At 80%, it's chopped only about 50% of the time, but the screen grab failed. As the condition worsens, it's chopped for longer durations, but staying at 1kHz period.

Re: Strange PCM3060 Failure Mode

PostPosted: Sat Jun 27, 2015 3:50 pm
by W4MMP
Hi,
If I may inject myself into this discussion. What is 1KHz? If HDSDR is set to a 10KHz LO offset the observed signal trace at DIN or VOUT(L+/-,R+/-) should be 10KHz. The audio voltage level at the output of U7 should be about 3Vp-p. (at full power). I don't have a measurement for the input to U7 (but I will take a measurement and let you know).

The key measurement I believe is, what is the voltage level at DIN when in failure mode. May I suggest it be measured when the rig is working and then when it is not. This will help isolate the fault area.

Re: Strange PCM3060 Failure Mode

PostPosted: Sat Jun 27, 2015 5:22 pm
by k1qn
Yes, I measured the RMS voltages, and they told me little. They fell in direct proportion to the RF output (also RMS). Chopping at exactly 1kHz was observed on the 'scope, and that frequency is used by the USB port. The chopping happens at 1kHz rate regardless of the input. There are threads on other forums relating to this event with other USB sound cards - 1kHz is constant.

I'm going to try to attach the scope trace again. It was too big the first time, and I'm following directly with AE9RB.

I was transmitting at roughly 1kHz, just to show that the signal was preserved when it wasn't being chopped. Even when I transmit at other frequencies, the chopping happens at a 1kHz rate, and the duration of the chops increases slowly so that it's the full 1msec. in 3-6 minutes.

As you can see, it was a nice evening on 20M JT65. :-)

Question: would the problem be caused by a bad or improperly installed U4 (ESD diode)?

At the moment, I'm testing my other, working, Peaberry (80/160M) to see if the same thing happens. I changed my station PC recently, and this is to see if it's the PC (insufficient DC power for the USB ports, etc...)

scopetrace.jpg
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