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Slowly fluctuating power and frequency after warm up

PostPosted: Thu Jun 18, 2015 3:21 am
by k1qn
It ran great for several hours. Then the power started oscillating on transmit. Period about 1 second. It got worse and the frequency started following the power variation. Finally went from full off to full on in maybe 2 seconds.

When I get a chance I'm going to reflow the voltage regulators the psoc and the pcm3060 ...and the si570.

In the meantime, help!

I was ringing digital without speaker but believe rx frequency also oscillated.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Thu Jun 18, 2015 2:52 pm
by k1qn
It's been running almost 4 hours w/o incident. The reflow may have fixed it.

Watch this space.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Thu Jun 18, 2015 3:32 pm
by k1qn
After 4 hours, it's back to it's deviousness. I'm going to check some voltages against nominal values...

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Fri Jun 19, 2015 6:51 pm
by n9seo
May check/recheck solder on r1 for marginal connections. This happened to me using kester 60/40 so I removed the solder here and reflowed with higher silver content solder. Your situation sounds almost like mine was in the early days. Mostly working but I would get wierd common mode voltage spikes on the fall and extremly noticable at the 0 offset of the LO. Eventually the spark/static fields would build up to the point it would make the PCM chip do strange things like lock up.

73 Kayne

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Fri Jun 19, 2015 9:27 pm
by k1qn
Now it'll run great for maybe 4 hours, then the power out will drop slowly and inexorably to close to nothing. This is similar to the behavior described in the instructions regarding the thermal fuse EXCEPT that there's no appreciable voltage drop across the fuse when things go sour.

I can fix it by removing the 12 volt DC for just an instant. Sadly, I can't do this remotely, which constitutes 98% of my operations. I reflowed all the solder on the board. The fluctuating power is cured now, probably due to a poor connection somewhere. It just goes for 4 hours, then the transmit power slowly diminishes.

Very puzzling. I have another Peaberry (160/80M) working flawlessly.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Fri Jun 19, 2015 9:28 pm
by k1qn
BTW, I have a fluke 85RF voltage probe.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Sat Jun 20, 2015 3:41 pm
by k1qn
All the DC voltages, plus (rf) QSE_I and QSE_Q are nominal when things go bad, which happens after about 2-4 hours of RX operation. The audio levels of all 4 outputs of U7 drop for no reason at this time. I reflowed U7, and I'm waiting. Next time it goes bad, I'll check the inputs to U7, which come directly from the sound card chip (give or take an RC pair). :-(

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Sat Jun 20, 2015 5:49 pm
by kz1x
Do you have a can of freeze spray? Example:

http://www.amazon.com/Professional-Freeze-Electronic-Component-FR-777-777/dp/B000Z99ZCA

It'd save you a lot of troubleshooting time.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Sat Jun 20, 2015 6:37 pm
by k1qn
After re-flowing the PCM3060 a few times, the TX is now a total fail. No audio at all. The RX still works, although it didn't a half hour ago. :-( I think the next step is to buy a heat gun, remove the audio chip and replace it.

Does anyone know any other strategies? The board is getting brown from all the rework done around the audio chip.

Re: Slowly fluctuating power and frequency after warm up

PostPosted: Sun Jun 21, 2015 5:18 pm
by k1qn
OK, now it'll run for an hour or so, then slowly diminishing TX power. It slowly goes all the way to zero, after maybe 5 minutes, then go back to nominal (1W).

I still think I may have a bad PCM3060.