Yamaha RX-497 turn off after 10-15 min

[coojoe213]

Hi all. I have this receiver, but after 10 min turn off.
I check the DC/PS values, and i see PS values are low. The normal values in service manual are DC:035, PS:068 . My DC is perfect 035, but my PS is...(my values are 53/52/51....47/46), every 5-10 second they are low. I check all electrolic capacitors in Power supply, but the are fine. C254 (22nf/650v) is 15nf when i check with my multimeter. Is this may be a problem or no? Can you tell what to try? :/


EDIT: Now, receiver turn off after 1 minute.

[Jeroen_Bezemer]

Check out the zenerdiode on the right part in front of the optocoupler. The led should only light when the voltage is high.

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[coojoe213]

All 3 zener is good and there voltages. I change the 22nf 650v Caps, but no result.
On S10 i have 9.7V
On +5M i have 5V
But on the display every 10-15 sec PS is lower :/

[coojoe213]

I found part of the problem. My +15V, every second is low. But i can't find which part make problem.

[mzacharias]

I found part of the problem. My +15V, every second is low. But i can't find which part make problem.

Is this the +15 volt line that comes from transistor Q121? If so, I would check to see if capacitor C145 might be open circuit. With a 'scope you can look at the collector or Q121 or at resistor R177 and see the nature of your ripple. It the ripple is properly filtered, the cap is OK, and you can look to see if the voltage drops coming out of the transistor. The transistor could be failing, going open emitter-base for example. Seen this problem many times, not on newer vintage Yamaha's but it's worth a check.