ideas on fixing amp?

[CommanderZero]

not sure if this fits under solid state or chip amp but here goes.

i have this older pioneer stereo amp that i bought back with me from japan, which i have been using as my desktop unit powering a pair of monitors and my sony V6's. but one day it just stopped working, the reply would keep buzzing like shown in the video. electronically everything else still works, i can change sources and sound modes, so i know at least maybe there arent any fried IC. what is heard through the speakers and headphone is a low pitched buzzing at the same rate as the relay, and when i plug a source into the unit it can be heard, theres no pitch though. you can only hear the rhythm, if you know what i mean. i disassembled the unit and cant find anything visually wrong with any of the boards. if anyone can figure out what might have gone wrong through what i explained and through the video, that would be very helpful. i know its not the best unit out there but it fits my needs perfectly and would be nice if it could be repaired. otherwise can anyone recommend anything similar? im very proficient at soldering so replacing any part in here would be no problem for me. thanks for any replies!

‪MVI 5534‬‏ - YouTube

[Frank Berry]

My first guess would be bad electrolytics in the power supply which feeds the output stages. I would replace all of the electrolytic capacitors in the amplifier.

[indianajo]

I second the motion. Electrolytics are the cylinders with a minus stripe pointing to one lead. Over twenty years old =garbage in my experience. A member here believes in measuring every one before replacing, but I have 3 dead meters with a "C" function, life is too short. In the last 2 years I've replaced electrolytics in 2 organs 1968 and 1964, 3 power amps 1961, 1970, 1998, a preamp 1961, a disco mixer 1998, and a 5 band radio 1979. One organ, one power amp, the preamp, disco mixer, and radio are done, reliable and sound great. Some of the others have issues besides the caps.
Mark the PCB before replacing with a sharpie; if you get them backwards they boil and leak. I suck the old solder off with old stripped wire and oatey #5 flux paste. Wash the PCB with a damp paper towel after this. No bigger than a WP25 iron. I like a 7/32" screwdriver tip for the iron. Use safety glasses removing, solder splashes.
If you like the unit, buy capacitors rated for 2000 hours up, and no surplus electrolytics. newark.com has the hours rating on the selector table, mouser requires you to download the part datasheet and read it.

[TRybak]

Could very well be old caps......another area to look at would be the rca solder points on the main circut board.....removing and plugging rca cables over the years can put a nice round crack in the solder around the pins resulting in hum, inferior audio quality, etc. Give them a good look at with a magnifier glass!

[Enzo]

Your caps may well be old and tired and in need of replacement, but if it just stopped working all of a sudden one day, that sounds like something other than just old worn caps. Bad filters usually comes in over time as increased hum and such. Of course a cap could just fail at any time, but that I think of separately from just old.


Good at solder? FIne. Try resoldering your main filter caps.

SInce you can hear the relay buzzing, no need for speakers until you cure the relay chatter. Got a scope? Look at the power source for the relays - look at its coil or on the diode parallel to its coil. Is there a lot of AC there instead of smooth DC? No scope? Set your voltmeter to work. Is the DC voltage on the relay coil more or less the rated voltage for the relay? FLip the meter to AC volts and remeasure that same DC. You are now measuring the ripple on that DC. It should be a small amount. If there is an AC voltage of several volts or more, then you have lost the filter cap on the relay supply.

FInd the main power supplies for the power amp output stages. Look at them the same way. I have no idea what the voltage is, but let us say 30 volts - positive and negative - for sake of discussion. Are both of them present, and smooth DC? Less than a volt of AC ripple?

Look at the outputs - the speaker connections. What is happeneing there. Is there some DC voltage appearing and disappearing with the relay closures?

[CommanderZero]

alright so i replaced all the capacitors in the power section, still got the relay buzz. anything else it could be?

[RJM1]

I agree with Enzo it sounds like it's the 12V supply for the relay, the time delay for the relay to turn on seems to be correct but when the protection circuit closes the relay it seems to chatter at 60Hz.

A model number would help.

[Mooly]

I wouldn't discount a shorted output stage (is it an STK ?) and that the short is killing the supply when the standby/power relay pulls in.

Power the unit up with a bulb tester and overide the relay with a link and see what happens.

[Original Burnedfingers]

quote:
I agree with Enzo it sounds like it's the 12V supply for the relay, the time delay for the relay to turn on seems to be correct but when the protection circuit closes the relay it seems to chatter at 60Hz.

Sounds like a bad cap in the timing portion of the protection circuit.

[CommanderZero]

model number of the amp or the relay? amp is A-P700