Bill S. says: "The only issue was that all of the [Processor Tech SOL] unregulated S-100 supplies were out of spec. This turns out to be a design issue, with a specific engineering note to address it (adding a bucking transformer) which I applied." - end quote Bill, for those not in-the-know: a "bucking transformer" reduces AC voltage by turning a transformer into an autoformer; by connecting the secondary in reverse and in series with the primary, to reduce the output voltage. One can also use a reducing transformer of course. That's too brief but some Web searching will explain further. Point being: many vintage computers of the 70's which use dem big transformers, expect line voltage to be 110 volts. Modern AC line voltage may be 120 volts; mine is about 122. I've had Heath/Zenith H89's blow up their regulator tantalums because the unregulated DC to their little DC regulators, exceeded the voltage ratings! Again, review H89 schematics for details. And of course, S-100 computers with non-switching power supplies and only a few S-100 cards to power, often produce excessively high unregulated DC voltages to the S-100 card DC regulators. As in IMSAI. I too have had to either a reducing transformer, rig a 12V AC transformer to "buck", and/or upgrade tantalum caps to higher voltage ratings (or replace same when they shorted). Or, just run the thing off a Variac. This was a good discussion. I will capture it for future reference, and possibly ask the participants privately if I can include their notes on my Web site; where I have similar information. Regards, Herb "pop!" Johnson -- Herbert R. Johnson, New Jersey in the USA http://www.retrotechnology.com OR .net preserve, recover, restore 1970's computing email: hjohnson AT retrotechnology DOT com or try later herbjohnson AT retrotechnology DOT info