MSOP CMoy Troubleshooting

[bperboy]

Okay, I'm doing repair work on my MSOP CMoy. A few months ago, the right channel cut out, and didn't work. I figured it was probably bad wiring in the pot, an Alps rk097, but I haven't gotten around to working on it until tonight. I totally rewired the pot, making very clean, deliberate connections, but there is still no sound in the right channel.

I've checked out both the input and output jacks for continuity, just in case there was a bad mechanical connection there. I was using a 9v battery that was running at 8.48v. Measuring from pin8 to ground (AD822), I get 4.25v, so the TLE2426 is working properly. I have sockets on the in and output pads on the board, so that might be a problem? I flipped around the inputs from left to right and the problem did NOT switch channels; when I did the same for the output jack, the problem DID switch channels. Maybe I should take out the sockets and hardwire directly? Or is there something wrong with the chip?

I did have this amp working for probably a month that I used it for, so maybe wear and tear caused the sockets to fail?

EDIT: I did also check the pot's resistances, and they checked out. I'm thinking more and more that these sockets are to blame, but I'd like to get a bit of confirmation before I go taking them off.

Thanks for the help,
bperboy

 

[Pars]

From your description and troubleshooting so far, it sounds like the opamp, since the problem did not change when switching the inputs, but did change when you switched the outputs. Have you checked DC offset on the outputs? If a channel goes in the opamp, it would be likely that you would have very high offset on that channel. Check all the way back to the opamp pins (1 and 7 IIRC for a dual opamp). If the offset checks out, it could be a solder joint on the opamp itself.

 

[bperboy]

On the right channel I get the same voltage as from pins 8 to ground. It might be the opamp then? Or the soldering?

Edit: I should try resoldering the pins, then switch the opamp?

 

[Pars]

By right channel, you mean pin 7 or pin 1? If so, opamp is toast. FWIW, when I was recasing a MINT a couple of years ago, I had the same thing happen. AFAIK, I didn't do anything to it, the opamp just went in one channel and DC offset went almost to rail (AD8620). Probably static or something. Hope you didn't hurt the phones you plugged into it, and don't plug anything good into it until it is fixed and you've checked DC offset.

 

[bperboy]

Pin 7, its the one in the right channel. I've only put cheapo earbuds in them, but I think they're still working fine. Thanks for the help, now I have to decide if its worth it to replace. Digikey is where I got the chip before, and it was about 5-6 dollars plus the $5 fee because it was less than $25, plus another $5-6 for shipping. Pretty much doesn't make it worth it, but I don't really want to waste the case and pot and jacks and all that. Hmm... decisions, I'm thinking about a Pimeta now, but I think it'll be too big for my tastes.

 

[Pars]

What opamp is it? You could always post a WTB in the forums for an SOIC-8 packaged opamp instead of buying new from Digikey.

 

[beerad]

Or someone might include it on an order, and drop it in the mail for you. I've placed 2 orders to Digikey this week, and will probably order again by the end of next week. I suspect a lot of people here are not averse to helping other DIY'ers. Lemme know if you want me to include it on my next order. It might be 2 weeks or so before you see it, though (order in 7-8 days, 2-3 days ship to me, 2-3 days mail to you).

 

[gjavitt90]

or you could order free samples from ti.com . they have the opa2132/4 which are pretty good.

 

[bperboy]

Quote:

Originally Posted by gjavitt90 /img/forum/go_quote.gif or you could order free samples from ti.com . they have the opa2132/4 which are pretty good.

The problem with this is that there is no MSOP version, so far as I could see. No worries though, I did find a source for the AD822 that was relatively inexpensive, so I went ahead and ordered.

For those interested, I did manage to desolder the old opamp successfully without ripping off any traces, as well as those in/output sockets, so I'm feeling rather pleased with myself right now!