Marantz PM8000 - No sound

allfine79

Member
2019-12-10 8:53 pm
Hi all,


I'm having an issue with my Marantz PM8000. In short, the amp went dead silent all of a sudden. When I power it on, everything seems to work as expected. The LEDs on the front panel turn on, and I can hear a relay clicking. Only the speaker output relay is not switching. It doesn't matter if I use the A or B speaker output, the result is the same.

I'm no expert but I find it highly unlikely that both relays (A and B output) fail at the same time. I'm assuming something else is wrong here. I've been measuring 24V DC on both sides of the relay coil. Also there seems to be a small DC voltage (about 0.2, 0.3) on one side of the relays that I think should not be there. That's measured between the relay and the 220R-0.25W (3151 in the schematic) resistor.

Any ideas how to debug this any further?

All help would be greatly appreciated...
 

rayma

Member
2011-04-29 8:37 pm
Could be an amplifier circuit fault, on both channels check for high DC output offset before the relay contacts,
and for correct power supply voltages +/-56VDC. If any faults exist, the TA7317P will trigger both relays open.

If no amplifier circuit faults, then check the protection circuit itself. It switches both L and R relays together.
Check pin 6 of the TA7317P for the trigger level. There are electrolytic capacitors that could be bad in the
protection circuit, or possibly the TA7317P itself.

Marantz PM8000 - Manual - Class A/AB Stereo Integrated Amplifier - HiFi Engine
 
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allfine79

Member
2019-12-10 8:53 pm
So, it turns out that B+ and B- are OK after all, I just had a voltage meter with a huge offset :-( I've replaced it so it should be OK now, but still... I it got me looking in the wrong direction.


Did some more research, and it turns out that +/-VB are completely dead. There's AC coming from the transformer, but it doesn't reach the rectifier, so no DC on the other end.

Looks like the 2 TR5 fuses (1215 and 1216 in the schematic) are dead. Not sure it this is a result of some other component failing. Or could they have died because of old age?

Can a TR5 be reset? Of do I just have to get new ones?

Any advice on how to continue is appreciated....