Yamaha R-V905 Won't power up

Been working on this unit off and on for a while. It will power on for about 1/2 second then power right back off. History on this unit is that for a while it started to power off on its own with no rhyme or reason, it progressively got worse to the point that it wouldn't power up. Display just barely appears before the unit turns back off.

I've checked the output transistors, they tested ok, also checked supply voltages, they appear good as well. I also resoldered any suspect solder joints I could find, still no dice. I don't have a full manual to work by, just some schematics for it.

Looking for a kick in the right direction...

Thanks, Benjamin Jennings snipped-for-privacy@yahoo.com

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by,

Many of the Yammies use some 4 pin regulator ICs. They are common failures. Usually the +5v ones, type PQ05RD11, and their output will drop typically to about 2v or so. When they go faulty, they tend to give just the symptoms that you describe. There are usually type PQ3RD13 around too. These are

+3.3v. I'm not certain if that model uses them, but have a look in your schematics, and if yes, have a careful check on their outputs with your DVM.

Arfa

Useless generic advice - and contradicts what the OP already said about this unit. The R-V905 has no thermal cutoff. It's detecting a power supply problem, though it could be falsely triggered.

Mark Z.

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Important safety note: A mains cable with an unshrouded plug on either end is very dangerous practise, especially in the UK. If you must have such a cable lying around , add some sort of springloaded shroud on one end. eg cable tie around the cable, to take one end of a spring and a small plastic bottle , cap end touching the other end of the spring. The bottle large enough to take the plug but deep enough when retracted to be reasonably enclosed.

ps could anyone explain to me why my newsreader has failed to pick up the jackhammer posting, no cross-posting AFAICS, checking on Google grouips, which does have that posting. About once a week it occurs in a thread I'm following.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Check the caps in the power supply.. You most likely have a bad one in the safety circuit and is shutting down due to a ripple in the voltage there. At least that is what I have found in a few amps I just recently serviced for a local business.

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