Advice on vintage Denon PMA-730

You are right, redk. Thanks for the good spot. The Matsushita relay has indeed another pin spacing, sorry about that.
The first thing to do now is to clean the relay contacts and see if the buzzing ceases.
This sounds good. Karl, how did you remove the cover from your Matsushita relay? Can I do it without desoldering and removing the relay from the amp?
 
Better not, Magreen. :)
You will work on it better with the relay removed from the amp. You need to clean those contacts and chances to damage them with the relay still on board are quite high.
 
Was thinking could be the relay, which might have the contacts consumed/tarnished by now. But the problem is not present through the headphones output, that comes after the relay. Try to clean a bit the speakers' A/B switches (above the Power button) with a contact cleaner. A new relay have to replace the stock one, IMO.

Below, a couple of pics from the stock relay in my PMA-737 taken some 3 years ago, not sure if your amp carries the same Matsushita relay. The second pic shows contacts tarnished which was the main problem with that amp...

jug6yf.jpg


idysdw.jpg


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Cleaning these contacts cured my PMA-737 acting like it had a dirty volume pot.
 
i have the same amp. great warm sounding, better than my NAD's cold sound. It does develop intermittent contact issues at the input switches when left unused for a while. have to press the input selectors hard or switch to different inputs back and forth to have good contact. It is hard for deoxit to reach its input push down switches so i have to live with it before i can find compatible replacement part. when the switch is not contacted well, the sound has some hiss or terrible frequency response.
the output power amplifying transistors of right channel was once burnt out. have to buy a pair of old replacement parts. if one of the push/pull transistor is not working, the sound will be distorted at higher volumes past 9 o'clock.
 
the output power amplifying transistors of right channel was once burnt out. have to buy a pair of old replacement parts. if one of the push/pull transistor is not working, the sound will be distorted at higher volumes past 9 o'clock.
Transistors can fail open, short or be intermittent. Might be another cause rather than outputs. Suggest use modern day replacements rather than
buying "NOS" off ebay.
 
Transistors can fail open, short or be intermittent. Might be another cause rather than outputs. Suggest use modern day replacements rather than
buying "NOS" off ebay.
it was shorted. you are right. those old but not new stock transistors were usually parts taken off electronic waste, so not guaranteed to work but very cheap. one NPN or PNP transistor in first shipment didn't work causing the issue i mentioned and asked them to send replacement and it worked.
 
--Update 4 years later!--
There was a lot going on back then in my life, with job, baby, travel... and I let this amp sit for awhile without turning to it. Then my smaller Denon PMA-300V amp recently bit the dust (protect mode, probably a failed power transistor... I have another thread on that, I think it's a lost cause) so I decided to turn back to this one

I opened up the relay. It was easy to pop the cover off it -- just squeeze the plastic sides and it came right off. I used a business card cut into strips, soaked in Deoxit, to clean and sand the contacts inside. And I adjusted the idle current with a multimeter while I was in there based on the instructions in the service manual.

The amp works!!! I've been using it for a few weeks now. It sounds beautiful, actually. I'm really pleased with it. Excellent clarity, separation between instruments, depth, and a spacious, three-dimensional sound. I actually can't believe it's working!

I really want to thank all of you, belatedly, for all of your patient advice in this thread -- especially Karl, JHB, mbz, Binkman, NAD, redk, and the rest of all the greatly helpful people here!

:beerchug:
 
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