Harman Kardon AVR-355 going into standby

[unilogic]

My AVR-355 switches itself to standby mode after a few minutes, when it becomes warm. If I turn it back on, it doesn't shut off anymore and can run for hours. If I let it cool down for a few hours and then turn it on again, it shuts off again after a few minutes. But no more problems if I turn it back on immediately. This always happens, even if the device is not connected to anything. I don't see a "protect" message or anything special. The device simply goes to standby (amber power button)
I did a complete reset of the CPU, but the problem persists...
I have attached the service manual, but I'm not sure which way to look. Is it a power supply problem, or is it the CPU forcing standby mode because it has detected an abnormal condition?
Pierre-Yves Andri, Belgium.

[stj]

Re: Harman Kardon AVR-355 going into standby

sounds like a bad cap,
try using a hair dryer to narrow down which part of the board needs to be warm.

[daron]

Re: Harman Kardon AVR-355 going into standby

there are two fuses on the transformer circuit board f110 and f111, harmon kardon recommends replacing them with 3.15a 250v fuses, should solve the problem

[unilogic]

Re: Harman Kardon AVR-355 going into standby

Hi Daron,

After buying a new AVR (Denon), I decided to repair this old and good HK AVR-355. So I located F110 & F111, but they are already 3.15A fuses.
To be sure, I decided to momentarily bridge them, but the problem is still there : switching to standby mode after 5..10 minutes
(but AVR remains ON if I restart it immediately, until next cold start).

Thanks for your suggestion anyway !

[debruina]

Re: Harman Kardon AVR-355 going into standby

1. Measure AC component on every DC voltage rails. Replace / check capacitors when to high.
2. Check IC36, IC37 voltage regulators. I have seen the negative gone bad a few times. Input selector gets hot when bad