Marantz PM80 trouble

[Radiant]

Hey everyone,

I recently picked up a Marantz PM80. Sadly, the amp began to malfunction in the first week I had it and eventually had the typical PM80 problem, being loud popping sounds and the amp jumping into protection mode. Still having paid a fair amount of money for the amp I decided to have a go at fixing it (mind you: I'm a complete analog electronics noob, but not a complete idiot because I do work with microcontrollers alot, just not the hardware that much ).
I replaced the STK3102 and improved the cooling by sticking small fin cooling modules to the cooling plate to hopefully keep this one from breaking (IC temperature now reaches about 40 celcius on class A). So far this has solved the popping/protection mode problem.

However, one problem from even before the STK3102 replacement remains, and that is that whenever the amp is turned on, the speakers are enabled/disabled with the buttons on the left or the muting is enabled/disabled, the channels seem to need to be kicked into life by swinging the balance knob to one channel, quickly turning up the volume to a high level, and repeating that for the other channel. If I don't, the channels will only play at a low (somewhat fluctuating) volume level and will make slight crackling noises. On headphones this does not occur.

Does this ring a bell for anyone or does anyone have pointers for me on where to look for the problem?

[glen65]

Originally Posted by Radiant

Hey everyone,

I recently picked up a Marantz PM80. Sadly, the amp began to malfunction in the first week I had it and eventually had the typical PM80 problem, being loud popping sounds and the amp jumping into protection mode. Still having paid a fair amount of money for the amp I decided to have a go at fixing it (mind you: I'm a complete analog electronics noob, but not a complete idiot because I do work with microcontrollers alot, just not the hardware that much ).
I replaced the STK3102 and improved the cooling by sticking small fin cooling modules to the cooling plate to hopefully keep this one from breaking (IC temperature now reaches about 40 celcius on class A). So far this has solved the popping/protection mode problem.

However, one problem from even before the STK3102 replacement remains, and that is that whenever the amp is turned on, the speakers are enabled/disabled with the buttons on the left or the muting is enabled/disabled, the channels seem to need to be kicked into life by swinging the balance knob to one channel, quickly turning up the volume to a high level, and repeating that for the other channel. If I don't, the channels will only play at a low (somewhat fluctuating) volume level and will make slight crackling noises. On headphones this does not occur.

Does this ring a bell for anyone or does anyone have pointers for me on where to look for the problem?

Not an exact diagnosis, but some basics.
The first thing to do would be to clean all controls and switches.
Next, any controls that are soldered directly to the PC board, resolder the connections.
There are also relays in the preamp section of this amp. you could have one with
some flaky contacts, dont forget the protection relays.
Check for bad solder joints on the PC boards. You may end up reworking connections
even if you cant visibly detect any.

[Radiant]

I think I might have an idea where it's coming from.. After some trying, I managed to get the amp working OK by connecting one channel to speaker set 1 and one to speaker set 2.
If I understand the schematics correctly, the only difference after the main amp section, is the relays. It has one for each channel (eg. one switches set 1 and 2 for the left channel, one switches set 1 and 2 for the right channel), and one (of a different type) which switches both channels for the headphones.
So, it seems one contact in both of the channel relays is indeed flakey. Does this make sense?

[Mooly]

It's quite possible. If the relays are able to be opened give the contacts a clean by drawing some rough paper soaked in iso etc through them.

[HMKD]

D701,d702,d703,d704 这几个一定要换, 及 rg01 故障。

[jitter]

Defect speaker relays on the PM80 aren't uncommon. My speakers have been connected to output 2 of my PM80SE for many years because on output 1 the L channel stopped working. Never bothered with fixing it...waiting for output 2 to fail too so that I can fix both in one go.

My amp also suffered the STK-problem and added to that I had to replace the reed relay for the headphone output.