Question To Other Techs. about Tascam 48 Relays

[SkywaveTDR]

I am working on a deck that was not well maintained but in this one I have found a lot of brown board around the mute relays as if they were shorted or overheating and this is on several cards. Has this been found by others? I am thinking of changing relays but they measure 900 ohms in card.

 

[SkywaveTDR]

Looking at the schematic it looks like the balanced amps are there as well and maybe this is due to those unbalanced adapters that short the negative active pin to ground. The level of incompetence is clearly displayed in this unit- lose screws, wrong screws, meters with wrong lamps and it goes on. It even had a tachometer on it that was not even from this model.
I have been changing out the 220uFd and 100uFd Marcon caps as I have found some shorted in other decks already. I don't think they age well.

 

[-mjk-]

Sam, that sure looks like heat to me, the way that solder mask has darkened. Do the relays have clear covers? Is the coating on the coils darkened also?

 

[SkywaveTDR]

These Mute relays are known for failure being the Omron nicked coil type which are sealed reed relays of the DIP type. I have been putting in Coto Relays with the IC sockets for easy replacement. So far I have not had any Coto relays fail. There is no way to look into them and being they are by themselves about 2000 ohms then they measure 900 in parallel they only draw about 12mA each. So is is likely that there is greater current going through the contacts than the coils causing this. Maybe it has to do with Phantom supplies going into the deck XLR connections- It is hard to tell where this is coming from. This is the first deck I have seen hot boards like this. This is them here-

 

[SkywaveTDR]