All good advice so far -- but one caution I forgot. My experience is that the CMOS chips from this period are THE MOST STATIC SENSITIVE chips that there are. It is much easier to damage these whith inappropriate handling than any modern stuff. Use paranoid static handling precautions. Since I usually work on these machines on those cold (dry) winter days when static forms easily, I also use a humidifier in the room where I work. -Rob -----Original Message----- From: cctalk-admin(a)classiccmp.org [mailto:cctalk-admin@classiccmp.org]On Behalf Of J.C. Wren Sent: Tuesday, September 24, 2002 8:08 PM To: cctalk(a)classiccmp.org Subject: RE: Altair-what do I do first A less painful way may be to lift the output pin of the regulator from its via. Or (and this is evil, but works, and is can be better than losing all your unsocketted chips), cut the trace after output of the regulator. You can always use a piece of foil tape or wire to effect a repair. This may detract from the ultimate value of the board, but you're far less likely to wreck it than removing irreplacable socketted chips. --John -----Original Message----- From: cctalk-admin(a)classiccmp.org [mailto:cctalk-admin@classiccmp.org]On Behalf Of Tony Duell Sent: Tuesday, September 24, 2002 20:24 To: cctalk(a)classiccmp.org Subject: Re: Altair-what do I do first _Neve_ plug in a classic computer without checking it first! [Good advice on electrolytic caps deleted] supply and check it out first. this, so you will have to transformer, but I have not unplug all of the cards and The amin problem with S100 systems is that the PSU lines on the bus are unregulated. The voltage regulators are on each card. And this means that a defective regulator _on a card_ will wipe out all the chips on that card, and may even put high voltages onto the bus lines and damage other cards. Therefore, do as suggested and get the unregulated PSU working first. Then take the cards (one at a time) and remove all socketed ICs. Make a diagram first, of course if you don't have the schematics/layout diagrams for that card. You'd better hope that the expensive/rare ICs (CPU, ROMs, RAM, LSI I/O chips) are socketed. Then put the (essentially bare) card in the backplane and check the outputs of the regulators on that card. Repeat for all the cards you have. Put the ICs back into a card before starting on the next one (unless you are a lot better organised than me!) Then, and only then do you put populated cards into the backplane and start testing logic functions. -tony