Ah, the TDA82822D part in the SOIC8 package is a good find.
Feeling much better now!

Digikey has it for a bit over a dollar (Mouser says a minimum buy of
2000).
Maybe hfsignals will move to the more easily gotten SMD part if they ever
roll the board.
Though I'm pretty sure I could solder the SMD into place with just some
short wires,
not bothering with the adapter board.

The chip is rated to work with a 4?? load so a 4?? resistor should do. I
doubt the chip would blow so fast that FB fuse wouldn?€?t protect it.

Yes, I think a 4 ohm resistor would probably do, I was getting rather
cautious when I saw how hard the M part was to obtain.
I'm suspicious that with a 12v supply it is close to the edge, they seem
to blow with little provocation.
Most of the datasheet seems to assume a max of 9v.
The fact that it works down to 1.8v reinforces this notion.

The fuse might protect it, depends on the failure mode.
The fuse costs about as much as the TDA2822D.

Jerry

On Wed, Feb 28, 2018 at 04:02 pm, Clark Martin wrote:

The TDA2822D in effect replaces the ?€?M?€? version. ??It appears the
same
except it?€?s an SMD part. ??You can get SMD to through hole adapter
boards
that would let you use one with the ??BitX. ??It would likely be cheaper
than buying the ?€?M?€? version.
??
??

The TDA2822D in effect replaces the ¡°M¡± version. ?It appears the same except it¡¯s an SMD part. ?You can get SMD to through hole adapter boards that would let you use one with the ?BitX. ?It would likely be cheaper than buying the ¡°M¡± version.

?

?

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:? ? ??/g/BITX20/message/42723

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.

On Feb 28, 2018, at 4:00 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

Better be a pretty darn fast fuse.

I'll go with an 8 ohm 1/2 watt series resistor to limit current.
At least till I find a good source for TDA2822M chips.
I'm fairly certain that resistor will offer sufficient protection.

On Feb 28, 2018, at 2:49 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:

So where did you get your spare TDA2822M's?

The TDA2822M is $7 for two on ebay, quite expensive for what it is.
Mainline distributors like Mouser and Digikey say it's discontinued.
ST no longer makes it, sources may be drying up.

My uBitx has a part on it marked "TDA2822M" but no ST logo, not sure who makes it.

The TDA2822M data sheet lists an absolute maximum one amp output output current. ?Since this chip is apparently prone to blowing out on short circuit?I would add a .5A fast blow fuse in the speaker line, between the PCB and the headphone jack. ?It doesn¡¯t need a fuse holder, it could be soldered in (using a fuse with pigtail leads). ?It would still be easier and cheaper to replace than the amp IC.

?

I¡¯ll likely add this mod to my ?Bitx. ?I don¡¯t intend to short it out but then almost no one does.

?

?

On Feb 28, 2018, at 2:22 PM, John <jjczon@...> wrote:

I fried mine when I plugged in a stereo sony noise canceling headset.
So it does not only happen with mono plugs.

Hopefully the spare TDAs with sockets will arrive soon so Incan start troubleshooting my no power problem.
To be on the safe side and avoid another wait I also ordered some IRFs ;)

But as CW seemed to work the first day I thought I had to look somewhere in the modulating circuitry. Have the schematics

I fried mine when I plugged in a stereo sony noise canceling headset.
So it does not only happen with mono plugs.

Hopefully the spare TDAs with sockets will arrive soon so Incan start troubleshooting my no power problem.
To be on the safe side and avoid another wait I also ordered some IRFs ;)