• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Pioneer M-90 Right Channel Problems

OlyDan

OlyDan

Member
I have a Pioneer M-90 power amp which I've owned for over 20 years. I bought it out of the broken pile at a pawn shop and with the help of a knowledgeable tech I was able to bring it back to life. I have had it in to a repair service twice since then and have had extensive work done replacing driver and power transistors.

The recent problem is that a few minutes after I turn on the amp the right channel goes out. If I turn the amp off and then turn it back on both channels play just fine and after that the right channel stays on indefinitely.

One puzzling thing is that when the right channel output stops the protection circuit does not come on. This is making me think the problem might be upstream of the power amp section. Does anyone have any suggestions.

Short of any easy fix suggestions, does anyone know of an audio repair tech located in Olympia, WA or nearby. The last techs that worked on it are out of business. Technician
 
Register to hide this ad
You should know Blhagstorm is possibly the closest reliable tech, based on your location. I do not have an M-90, I have an A-90. Not sure how similar they are, but if the M, is somewhat similar to mine, fixing it is not a easy. I strongly suggest you ask Blhagstorm and see if he is willing to take it in for service.
The problem here is not just a bad relay. This amp is also due for service base ind on its age. If you want to have it for another 20 years, get it serviced professionally.....the right way!
 
Wow, Thank you rottalpha, blhagstrom and Binkman. The thread blhagstrom linked to is very informative. Yes, I agree that the problem is probably related to one of the relays. When I first acquired the M-90 back in the early 1990's the problem was a dirty relay. I cleaned the relay contacts and was good to go for several years.

I am leaning towards asking blhagstrom to take on the job of tracking down the issue. I love this amp and as can be seen from my tag line the M-90 is the jewel in the crown of my Pioneer Reference system. My solder slinging skills are not what they used to be. Duvall is not that far from me and as I am retired I do enjoy day trips.
 
Well I decided to open up the amp and check out the relays. I've checked out RY301, RY302, RY303, RY304, RY401 and RY402. None of these are opening up when the right channel goes dead. Also, it makes no difference whether I select control amp, cd direct or line direct for input, or if I select speaker A or speaker B.
 
No joy so far but thanks for asking Binkman. My next plan is to use some freeze spray to see if I can identify the circuit and specific part that is causing the problem. I was out of freeze spray and no that Radio Shack is out of business I had to track down a different source for freeze spray.
 
I now have had joy!. I tracked the problem down to a cold solder joint on the right amplifier board. It was so sensitive that a slight tweaking of the board almost anywhere would cause it to cut out. Without the freeze spray I don't think I could have localized it. I finally identified the specific joint by pressing on it lightly with the point of an exacto knife.

Now the bad news. I have somehow buggered up the speaker selector relay. I had taken the cover off of Speaker A relay and after putting it back on there is not signal to Speaker A. The relay is still working but no signal comes out of Speaker A. I'm going to sleep in this and discover the easy resolution tomorrow.
 
Well its a new day and a fresh approach. I used some very fine grit sandpaper to burnish the contact points on Speaker A relay and now I have sound coming from the Speaker A binding posts.
 
My treasured Pioneer M-90 is up and running like it should be. Its all buttoned up and back in the system. Thanks for the input. It gave me inspiration to keep at it until I found the problem.
 
Buonasera. Seguo molto questo forum, sei il migliore al mondo nell'annata hi fi. Vorrei porre una domanda. Possiedo un pioniere m90a, funziona benissimo, recentemente aggiornato con nuovi condensatori e transistor. La lampada di protezione non funziona. Non ha mai funzionato Quando l'amplificatore è acceso, la lampadina è rossa, quindi gialla. Tutto funziona bene nel mio amplificatore, ma nessuna luce si accende, né rosso né giallo. Le due lampadine sono buone. Quale potrebbe essere il problema? Qualcuno può aiutarmi? Grazie a tutti.
 
Sorry, I don't speak Italian. If someone would be so kind as to translate the above message to English I would be thankful.
 
This is what Google Translate gave me when I entered your message in Italian:
Good evening. I follow this forum a lot, you are the best in the world in the hi fi year. I would like to ask a question. I own a m90a pioneer, it works great, recently updated with new capacitors and transistors. The protection lamp does not work. Never worked When the amplifier is on, the bulb is red, then yellow. Everything works fine in my amp, but no light turns on, neither red nor yellow. The two bulbs are good. What could be the problem? Can someone help me? Thank you all.

Your post seems to say that when you turn on the amplifier the red light comes on at first and then the light turns to yellow. If that is what is happening then the amplifier is working properly. However, something may be getting lost in the translation.
 
Good evening. I own an m90a pioneer, it works very well, recently updated with new capacitors and transistors. The protection lamp does not work. It never worked. When the amplifier is turned on, the light bulb is red, therefore yellow. Everything works fine in my amplifier, but no lights come on, neither red nor yellow. The two bulbs are good. What could be the problem? Can someone help me? Thank you all.
 
La ringrazio per la risposta. Ho avuto l'M90a con me dal 2004. Acquistato su eBay. Ha sempre funzionato bene. Ho scoperto con altri M90a che quando si preme il pulsante di accensione si accende una luce rossa, dopo il relè questa luce diventa gialla. La mia M90a non ha mai avuto luci, ma ha sempre funzionato. Di recente ho apportato un aggiornamento ai condensatori e ai transistor per i driver. Ho usato KSA1381 e KSC3503 in sostituzione di A1145 e C2705. Tutti i condensatori sostitutivi, anche i big 4, con nichicon UPW. L'M90a suona bene adesso, ma ancora non si accende la luce quando premo il pulsante di accensione. Ho smontato il pannello frontale, ho sostituito le due lampadine (una coperta di rosso e una coperta di giallo) con altre originali. Non si accendono ancora luci, ma la mia M90a funziona perfettamente. Chiedo il vostro aiuto se qualcuno ha una soluzione per alimentare queste due lampadine. Grazie a tutti
 
Thank you for the reply. I have had the M90a with me since 2004. Purchased on eBay. It has always worked well. I discovered with other M90a that when you press the power button a red light turns on, after the relay this light turns yellow. My M90a never had lights, but it always worked. I recently made an update to the capacitors and transistors for the drivers. I used KSA1381 and KSC3503 to replace A1145 and C2705. All replacement capacitors, even the big 4, with nichicon UPW. The M90a sounds good now, but the light still doesn't turn on when I press the power button. I disassembled the front panel, I replaced the two bulbs (one covered with red and one covered with yellow) with other originals. No lights come on yet, but my M90a works perfectly. I ask for your help if someone has a solution to power these two bulbs. Thank you all
 
You must log in or register to reply here.
Back
Top Bottom