TU56/TC11 restoration - Power supply question

On Wed, 2005-03-16 at 17:53 -0500, der Mouse wrote: Nor me, but a recent tale... I tried bringing that Sun 2/120 up the other day, and one of the big filter caps on the output side let go with an impressive hissing and *masses* of smoke. Funny thing was, it had been brought up after many years dormant on light load first (I didn't want to risk any of the boards in there!) and allowed to sit for a bit like that. Tested voltage levels and they were OK, so shut down and fitted all the boards. Back up again, all voltage levels OK. It ran like that for maybe 30 minutes, and only then did one of the big caps fail. Luckily they had safety valves otherwise it would have been a rather impressive explosion. Thing is, a variac wouldn't have helped at all - everything checked out. Things were up to temperature well before the cap blew, and there wasn't anything we did to put the PSU under any stress at the point when it broke (*unless* something died and shorted in one of the boards). So cautionary tale is not to stick your eyes near *any* big old caps in running equipment I suppose, no matter how good they are! I've replaced the dead cap (and its twin just to be sure) - the blown one failed as a dead short. Ran for about 30 mins on a dummy load and it was giving out useful voltages. This weekend I'll get to see if any boards in the machine were cooked by the failure, but I'm hopeful that the destroyed cap was the only casualty... cheers Jules