Yamaha R-V905 Won't power up

Open up, check your power transistor/mosfet temperature after it power off, if hot then it proofs your thermo cutoff is working. Next figure what causes it to overheat.

 

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








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As the display goes out , is it a switch mode power supply ?

 

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.

 

Loop the main (polarized!) power cord back into one of the switched outlets
at the rear. Run a double - ended polarized cord from the other switched
outlet to your variac or switched power strip. In this way you can bring up
all the internal voltages without regard to protection status.

A few Yamaha models had problems with the backup cap leaking near the
microprocessor and causing problems like this - but I'm thinking your model
is NOT one of these. Worth keeping in mind, though. If it comes to
troubleshooting the protection function of the micro I can probably help.
Post back here or you can e-mail me direct at:



and revers the domain name to read sbcglobal.net


Mark Z.

 

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.

 

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.

http://webpages.charter.net/jamie_5"