PC/AT "power good" problems

Richard Cini rich.cini at verizon.net
Sat May 28 16:37:42 CDT 2016

All –


I pulled my old PC/AT off the shelf to see if I could get Windows 1 running on it (since I just located the Windows 1.04 SDK which I have running in Bochs). It worked when shelved years ago, but it unfortunately suffered some case damage from a leaky battery. No damage to the mobo or cards thankfully. I replaced the battery with a 4-AA pack.


Basically, the PC won’t come out of reset. I tested the power supply with a load tester specifically for PC power supplies and it reports power_good and all voltages look good on a meter. So far, so good. I dug out my ISA POST diagnostics card which also has a PG tester in it. This reports no_PG but I do see the reset pulse on the bus. Not sure why one would report OK and one not. 


I have a spare generic power supply (which also tests good using the same tester) and produces the same result. I have no cards installed but I tried it with floppy/hard drives both connected or not connected. 


I traced the PG signal from the power supply through the 82284 clock driver/ready interface chip and the PG is definitely there (transitioning L->H on power-on) and RESET is transitioning H->L.


                Any recommendations on where to go from here? Does anyone have an extra PC/AT motherboard they would be willing to part with? 


As an aside, would this have been a typical development machine? AT was introduced in August 1984 and Windows 1.04 was released in 1987 so I’m guessing probably.







Rich Cini



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