Rotel RA-971 repair

[drbenjamin]

All

I have a Rotel RA-971 I bought 16 years ago. Recently the right channel stopped working, no sound. Symptoms (right channel only):
1) No sound from any input (e.g. AUX 1, CD, tuner)
2) No sound when swapping input channels
3) No sound speakers or headphones (haven't checked tape out)

I opened it up and checked all 4 fuses which were fine. All the capacitors also seemed OK, no bulging or leaking. I am presuming that since the headphones don't work my problem is the preamp, which I believe is a OP2604 (The circuit diagram is available here ROTEL RA-971 SM Service Manual free download, schematics, eeprom, repair info for electronics , the download link will appear after a 1 min wait). I have a voltmeter, soldering iron and rudimentary skills I'd love to bring the amp back to life, and would appreciate any help

1) Is it possible that swapping the 2604 would fix the problem? I'm not an EE but I didn't think ICs failed after 16 yrs
2) Are there any tests I should run to help diagnose (e.g. check voltages at the input pins of the 2604, or would they be too small?)

Thanks for any suggestions!

 

[anatech]

Hi drbenjamin,
1.) probably not unless you did something to it specifically.
2.) leave the poor thing alone. The other channel works, so it has power.

Check your tape outputs. The headphone out normally runs off the power amp.

-Chris

 

[Mooly]

Have you measured the fuses i.e. not just a visual check ?

 

[drbenjamin]

Chris

Thanks for your reply! I checked the tape outs and they both worked, I was led astray by a post I'd found that said both tape out and headphones came from preamp.
I then put my headphones in the headphone jack, sound from left only. I toggled the tone knob (which I had done before) and both channels started working, so I'm guessing I have dust inside that switch. (didn't realize it was a 2 channel switch!). Should I use compressed air only or would you recommend a contact cleaner?

 

[drbenjamin]

Have you measured the fuses i.e. not just a visual check ?

Hi Mooly, thanks for the reply. Yes I used my multimeter on all 4 fuses.

 

[Mooly]

So it sounds like you have a poor connection within the switch or.... it would also be worth checking the soldering on the underside of the switch area actually.

Everyone has their own ideas on cleaning switches... and you can get proprietary stuff. I think 'Deoxit' is a favourite (geez... how much ) or there are others,

PRO POWER - PPC110 - CONTACT CLEANER, 200ML AEROSOL | CPC UK

DEOXIT - D5S-6 - CONTACT CLEANER 5 OZ. CAN | CPC UK

 

[anatech]

Hi drbenjamin,
Use as little cleaning solution as you can to restore operation. IPA would be my first choice, followed by any of the zero residue electronics cleaners, and then something along the lines of General Cement De-ox-id. This is a fluid, available by the 2 oz bottle. Use a glass syringe to apply it with the tip removed from the needle. I would love to get more of those as I use the two I have. The other is for applying fine oil.

I'm glad you don't have a serious fault.

-Chris