Marantz PM55 Amplifier. Speaker relay dropping out. - UK Vintage Radio Repair and Restoration Discussion Forum

samjmann · 24th Jul 2015, 9:51 pm

Hi

There's been a few posts on here and elsewhere about these amps suffering from the speaker relay 'dropping out' for no apparent reason. This one would mute at random, no amount of heating, freezing or tapping would provoke it.

After much running the amp finally faulted with the meter connected.
The mid-point was a healthy 6mV normally, but would rise past 100mV+ on each channel for no reason, the relay then tripped. I had a hunch that the input condition to the output stages might be being upset.

The fault was that the ground of the two input leads to the o/p board sometimes lifted to -2.5v! This was caused by dry joint at each end of the o/p pcb where the metal frame is used as a ground jumper link.

Anyone remember the RBM A774 hybrid chassis that suffered similar problems?

Cheers, SJM.

paulsherwin · 24th Jul 2015, 10:09 pm

I finally got around to looking at my PM66SE recently (discussed here) and resoldered all the joints on the relay board. The fault seems to have gone away, but it's always difficult to be sure when a fault is occasional and intermittent. Time will tell.

Unfortunately the fault was too intermittent to take any meaninful voltage readings.

24th Jul 2015, 9:51 pm	#1
samjmann Heptode Join Date: Feb 2014 Location: Nottingham, UK. Posts: 648	Marantz PM55 Amplifier. Speaker relay dropping out. Hi There's been a few posts on here and elsewhere about these amps suffering from the speaker relay 'dropping out' for no apparent reason. This one would mute at random, no amount of heating, freezing or tapping would provoke it. After much running the amp finally faulted with the meter connected. The mid-point was a healthy 6mV normally, but would rise past 100mV+ on each channel for no reason, the relay then tripped. I had a hunch that the input condition to the output stages might be being upset. The fault was that the ground of the two input leads to the o/p board sometimes lifted to -2.5v! This was caused by dry joint at each end of the o/p pcb where the metal frame is used as a ground jumper link. Anyone remember the RBM A774 hybrid chassis that suffered similar problems? Cheers, SJM.

24th Jul 2015, 10:09 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,944	Re: Marantz PM55 Amplifier. Speaker relay dropping out. I finally got around to looking at my PM66SE recently (discussed here) and resoldered all the joints on the relay board. The fault seems to have gone away, but it's always difficult to be sure when a fault is occasional and intermittent. Time will tell. Unfortunately the fault was too intermittent to take any meaninful voltage readings.