Adcom GFA-555 Blew main fuse after turning on in bridged mode

[jetblac]

Hello.
Just picked up a Adcom GFA-555, all was fine. The next day I bridged it, (properly) when I turned it on the main fuse blew. Okay ... so I put it back in stereo mode, and it blew the main again. Okay ... next time I removed all of the rail fuses, and it still blew the main. Does this sound familiar to anybody? I can try to get my money back or haggle for a discount since it is broke, but as you can tell, I have no idea what I am getting into.

Back story: I have another 555 that was bridged to the other speaker and that one is still fine.

Chime in, if you can. Thanks

 

[jackand08]

If it still blew the main fuse even after you removed the rail fuses, then (assuming that the rail fuses remove any kind of connection between the transformer and the amplifiers) it looks like you may have a faulty mains transformer. How this could've been caused by a faulty bridge mode, I don't know as transformers usually hold up pretty well against faults on the secondary side.

Why it blew the first time may be difficult to say, but it could've blown the second time due to the wrong fuse type being used. Did you replace it with a slow blow/time lag fuse?

Also, when wiring it in bridge mode, did you wire the speaker between the two positive outputs of the amplifier (neither speaker lead grounded)?

 

[Mooly]

Top off, and measure the output transistors for starters. See if any are short circuit.

Those and the bridge rectifier, I can't see it being anything else tbh.

 

[east electronics]

common failure is the bridge rectifier.... for this amp there is no soft start circuit and the singlest trigger in the power could easilly short the rectifier ...

kind regards
sakis

 

[jetblac]

Did you replace it with a slow blow/time lag fuse?

Also, when wiring it in bridge mode, did you wire the speaker between the two positive outputs of the amplifier (neither speaker lead grounded)?

Slow blow? there was an AGC in there.
and yes, it was wired correctly.