Marantz Amplifier PM385 - Nil output

[ivonj]

I have a Marantz power amp PM385 with NIL output. The relay does not click when the power amp is switched on. I have checked the power transistors at the output, all seem good.

I suspect the relay circuit to have some faulty component, but I cannot locate the relay on the board. Can anybody point me where to look for the relay & circuit.

Thanks.
Ivon

[homertooties]

Hi there the relay will be a rectangular plastic box normally blue or black,usually 2 or 3 transistors around it with 2 diodes and couple of resistors,capacitors,normally the switch contacts will connect to the emitters of output transitors through the emitter resistors....hope this helps....

[ivonj]

Thanks homertooties.

The only plastic box that I can see is a black one which is also used for the stereo headphones. Is that possible, headphones with relays inside?

[homertooties]

Hi i would not have thought so ,normally the headphones jack sometimes has sprung contacts inside ,so when you insert your headphone cable the output to speakers is cut off,any chance of a picture of the main internal board on this amp?or a schematic?

The only other place i can think of a relay is near where the power cable comes in on rear...

[90975838]

why not take a photo on the PCB?

I've PM350 schema, don't hv any relay inside.

please specify how you test the output transistor

hope this help!

[ivonj]

I measured the output transistors by taking them off the board -there is a pair of 2SC3182 & 2SC1265. Using a digital meter, with the knob set to measure diodes, I measured the forward and reverse bias for b-e, b-c and c-e for all 4 transistors.

In case of 2SC3182:
b-e and b-c = 0.550 V (forward bias), reverse bias = open
c-e = open in both directions
gain = 86 for one and 73 for the other.

In case of 2SC1265:
b-e and b-c = 0.510 V (forward bias), reverse bias = open
c-e = open in both directions
gain = 187 for one and 131 for the other

After thinking well, I remember that under normal operation, after switching on the amp, there would be a delay of 3-5 seconds before i would hear a little 'pack' sound in the speakers. Hence, there might be a on-delay circuit that would turn on the output transistors and no relay as suggested by member 90975838.

Member 90975838, can you send me the schematic for PM350. That would be great. Thanks.

See attached image for PM385 board.