Adcom GFA-555 mismatched input PCB

[ndemarco]

Hello,
It's apparently customary to start these posts with "Yes, sorry. It's another Adcom GFA-555 thread." So... Yes, sorry. It's another Adcom GFA-555 thread. I'll refrain from calling it a Triple Nickel or any other cute affectation.

Basically, I have a GFA-555 that has a totally borked input PCB. I have the service manual. The input PCB does not really match that well with the service manual. Namely, the component layout is fairly different.

The service manual shows a board 2714-0-1. My board is marked 17-087.

It is a 555, not a 555 II. The board has no ICs, just passives and transistors.

Am I crazy in hoping to find a good schematic and board layout for by broken down board? Better still: Anyone got one?

Thanks,
Nick

 

[planemusic]

Hi Nick,

Did anyone ever get back to you on this? I'm in a similar situation.

Thanks,
Ryan

 

[rayma]

I'm in a similar situation.

This should help.
New Adcom GFA-555 MK1 Input boards! | Hoppe's Brain

 

[Phloodpants]

Does your 555 have a vertically mounted input board? With part numbers in the 600 range, i,e, Q601?

I am actually working on a version of the 555 board to fit these more rare, early 555's.

I've also seen a couple 555's that had horizontal boards like the later and more common version, but totally devoid of silk-screening, which makes troubleshooting a nightmare. These also utilize older-technology MPS type transistors with the EBC pinout, so the layout is different from later boards. However, these amps are compatible with my replacement board, so no matter.

 

[planemusic]

The board isn't vertical. I've read about these. Mine is horizontal but, as you stated, totally devoid of any silk-screening. It does us older MPS type transistors with the EBC pinout.

The amp is destined to simply be sold but I think I'll order one of your replacement boards. Thanks.