Assuming the sound is good in both channels before the amplifier shuts down, it is likely to be a problem in the protection circuit of either power amplifier output stage. This could be as simple as one or two small electrolytic capacitors associated with a specific protection IC like µPC1237 or an equivalent discrete circuit. Without a model ID and appropriate schematic, this won't be simple or easy for you or others trying to assist though.
If you can locate a free schematic, by all means link or post it as appropriate.
If you can locate a free schematic, by all means link or post it as appropriate.
OK, there is a clear copy of the service manual here: Philips AH380 - Manual - Stereo Power Amplifier - HiFi Engine (registration required)
The amplifier has discrete component current limiter circuits, thermal sensors and over-current sensors for both channels. There are also indicator LEDs showing thermal or overload faults. Do any light up when the amplifier shuts off?
Do you hear a click from the speaker relay after you power on?
Do you have good sound before the amplifier shuts off after a few minutes?
Do you hear a click when the amplifier shuts off ?
It may be beyond your skills and equipment to repair but before going further, you will need to make and use a dim bulb tester, AKA lightbulb limiter to allow you to operate the amplifier safely (i.e. without damage to it whilst testing). Googling will find dozens, maybe hundreds of schemes for assembling one of these simple gadgets from some domestic electrical fittings, an insulated electrical box or similar and a discarded power lead. You will also need an old style incandescent lightbulb of 60-75W to use it here.
The amplifier has discrete component current limiter circuits, thermal sensors and over-current sensors for both channels. There are also indicator LEDs showing thermal or overload faults. Do any light up when the amplifier shuts off?
Do you hear a click from the speaker relay after you power on?
Do you have good sound before the amplifier shuts off after a few minutes?
Do you hear a click when the amplifier shuts off ?
It may be beyond your skills and equipment to repair but before going further, you will need to make and use a dim bulb tester, AKA lightbulb limiter to allow you to operate the amplifier safely (i.e. without damage to it whilst testing). Googling will find dozens, maybe hundreds of schemes for assembling one of these simple gadgets from some domestic electrical fittings, an insulated electrical box or similar and a discarded power lead. You will also need an old style incandescent lightbulb of 60-75W to use it here.
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