Re: UBitx no audio! Could use some advise

Brett Deschene

Ok! So I tried what was suggested and here is what I found. 
R253 was bad and  I was able to replace but that did not fix. 
I suspect a blown TDA2822M. I have one on order, so now I wait until it arrives and I swap it out.  If there are still issues I will continue to work the problem and post if I get stuck again. Thanks Jerry!

-Brett Deschene

On Feb 28, 2018, at 10:59 AM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Remove PA-PWR from the rig so the IRF510's won't be working, then try sending CW.
Does the sidetone come through the speaker?  If not, you have a very simple 
path from CW-TONE to the speaker to debug.  Perhaps wire a speaker between 
the junction of R250,R251 and ground, should hear the sidetone there if it's coming 
out of the Nano properly. 
If not, triple check connections at the volume pot and out to the speaker.

Many here have reported a blown TDA2822M, apparently due to shorting the speaker line to ground.
Probably best to add a series resistance of 4 to 8 ohms at the output of the TDA2822M and/or
reducing the supply voltage to the TDA2822M:

If you suspect a blown TDA2822M, you could of course swap that chip out.
Hard to get as NXP has discontinued manufacture, perhaps now cloned in China?
An alternative is to google for "lm386 kit", and wire that into the volume control pot.
Perhaps permanently.

If you hear the sidetone when transmitting CW but no receiver audio, try soldering a wire
across nodes M1,M2 in case the relay at K2 is not working properly.  Does that fix receiver audio?

Can you hear a pop when stroking C50 with a screwdriver?

Beyond that, perhaps try the tricks shown in this video on receiver debug.
The wire he uses is just 3 or 4 feet of hookup wire, nothing on the other end,
it is acting as an antenna to pickup up random noise.

Be sure to restore the hacks I suggested (PA-PWR removed and M1,M2 short) before
trying to operate the rig.

Jerry, KE7ER

On Wed, Feb 28, 2018 at 04:20 am, Brett Deschene wrote:
Audio is completely nonexistent. No sidetone heard from CW, no static, hissing, popping, nothing.
I am pretty sure the issue is something simple and located on the board somehow but even with the schematic of the received audio path I just do not know how to diagnose and am not sure where on the board to take readings. Any help would be much appreciated.

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