Arfa Daily wrote:

Anyone got the schematics for a Crown XLS5000 ? I'm most interested in the
board that the mains comes in to. There's a bloody great disc something
inside a big lump of heatshrink, and serious flames shoot out of it before
every trip and fuse in the workshop goes out ...

If I bring it up on the variac, I can't get beyond about 20 volts before the
poor thing is jumping off the bench, so there's a good short on there
somewhere. I initially thought that the disc might be a big VDR that was
short, but looking up the part number on the second one that's on there for
the other half of the amp, it appears to be an inrush thermistor, so I guess
whatever is short, must be south of that ...

** I found a nice pic:

http://www.musiker-board.de/attachme...005-jpg.84415/

The XLS series of amps use large, 240VAC rated PTCs for inrush limiting AND fault protection. Room temp resistance is a few ohms rising to over 12kohms when hot. Normally, the relay next door bridges it out soon as the DC rails come up.

The example I saw late last year was an XLS602 that would simply not switch on while the PTC was getting very hot. Like yours, you could variac it up to some extent, then the PTC detected a fault and went high.

Problem turned out to be the toroidal transformer, enamel insulation had failed in the primary winding creating shorted turns.



BTW:

Very sad to hear of George Cole's passing.



..... Phil