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...
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...
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
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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You may want to look at THIS THREAD which deals extensively with the TA7317 protection chip. A copy of the data sheet is attached.
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....
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....