Stereo buzz until unit warms up

[eKretz]

I've got a surround received that's been in use in my living room for probably close to 15 years now, and recently it's started acting up. First it started as having no audio for a few minutes when it was first turned on for the day and cold (all inputs) but then working perfectly after warming up. Then recently it has started with what sounds to me like a 120Hz buzz instead of the silence. Volume knob raises and lowers the volume of the buzz, and again after warming up the audio is completely normal. The buzz volume fades out as the unit warms up.

Obviously the issue is somewhere after rectification with the noise being 120Hz. I'm thinking maybe a filter cap or several? I've opened the receiver and haven't seen any obvious failing caps - no bulgers or leakers. I have a meter that can check the ESR of the caps - would it be better to start checking in the power supply board area probably?

The receiver is an Integra DTR-9.1 if that helps any - I have a set of schematics and "service manual" but forget where I got them from - have had them for years just in case. The service manual doesn't really give much diagnostic info, hence the "".

 

[Harald Kapp]

a 120Hz buzz

This sounds typical for defect electrolytic capacitors in the power suppply - not uncommon after 15 years of service. The 120 Hz come from the rectified 60 Hz mains which are normally smoothed out by the electrolytic capacitors.
Remove mains, open the receiver and locate the big electrolytic capacitors in the power supply. Get replacements matching the ones present as good as possible (higher voltage and/or capacitance is o.k., no lower values should be used). Exchange the electrolytics and you should be set.

 

[eKretz]

Yep, snatched out the 2 PS boards and removed all the large caps from the parallel banks to test out of circuit. Five Nichicon 2200uf 35V caps were in very bad shape - actual measured capacitance varied from 95uf to 340uf, ESR that should be in milliohm range measured from 10 ohms to 32 ohms! Caps still look cosmetically perfect.

 

[dorke]

If possible replace the bad caps with "computer grade" caps of 105C (temperature) ,
and take care not to get Chinese counterfeits ,don't by them on Ebay !

 

[eKretz]

Thanks for the advice, they are on the way from Mouser already, went with Nichicon again. They were originally 85°C rated, I ordered 105°C rated replacements. I was actually kind of surprised to see that they were 85°C - this receiver was top of the heap in its day - I think it was close to $2k new.

 

[dorke]

It is an Onkyo isn't it?
They suffer from a lot of heat related problems in ICs as well.

 

[eKretz]

Yes, it's their fancy "boutique" line or whatever. Sort of like Acuras are fancy Hondas. It's a great receiver other than this failure, sound is outstanding, power is pretty good and very clean and tight - and very low noise. 15 years of service isn't too bad - though I can't help wondering if it would have lasted quite a bit longer if they had installed 105°C caps instead of 85°C caps.

 

[eKretz]

New filter caps did the trick, the receiver is good to go now.