[vcf-midatlantic] PDP-11/10 PSU Repair/Warning

Herb Johnson hjohnson at retrotechnology.info
Fri Jun 7 11:29:18 EDT 2019

This caught my eye, so I looked at the schematic. Ironically, the 
shorted full-wave rectifier is shown on the "power-fail" circuit 
drawing. But the rectifier supplies all the unregulated DC voltage. 
Unfortunately the fuse F1 is *after* the rectifier and not before. Thus 
adding a fuse before the rectifier is wise.

Bypassing the now-destroyed edge-connector pins is also wise. Did you 
determine the normal AC current on those pins? I suspect a few amps, 
thus those pins are at risk anyway.

Thanks for calling this repair out. It's a cautionary tale about vintage 
power supplies in general; look for AC-side fuses, install if not. I"m 
looking at an IMSAI; the prior owner bypassed the AC fuse holder! ;(


Herbert R. Johnson, New Jersey in the USA
http://www.retrotechnology.com OR .net

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