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XT Power supply failed...

vwestlife

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Did you try disconnecting the motherboard, and see if it powers up when connected to only the drives? One or more of the 30-year-old capacitors in the system may have failed as a short circuit. Usually the power supply will just explode these bad capacitors with a loud bang (my 5150 case has a burn mark on the inside of the cover to prove it!), but maybe yours is actually smart enough to detect the short-circuit and shut itself down.
 

Al Hartman

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Doubtful.

I found on eBay, an ATX to AT Power supply adapter for under $7.00. So, I ordered one. That will let me try a different supply to see if my motherboard is still good, and I can somehow fit in an ATX supply until I can find a suitable replacement.

If the rest of the system works, I can finish the two XT-FDC cards I'm building.

Maybe I'll come across a 5160 or a Tandy 1200 to replace this with.
 

Stone

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Caps can short quietly without an obvious flash or burn. It's not a required symptom.

It could be an expansion card, a drive or even the keyboard. You should try with all those removed before you *assume* it's the power supply or motherboard.
 

Al Hartman

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The adapter I bought didn't work. No Power, nothing on two different logic boards.

I ordered another more expensive cable to see if it will work. The floppy controller chips arrived today, but I can't flash or test the two XT-FDC boards without a working system.
 

Chuck(G)

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Stupid question, Al, but did you short the power switch pins on the adapter when you tested it? Forget the line switch--that's not the way modern PC power supplies work.
 

Al Hartman

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Nope. It's not a stupid question. I'll go buy a switch and something to load the P.S. when I get a chance, but meanwhile I ordered a better version of it. I have a 486 board here now too (a gift from a friend.)

I will probably buy an ATX case to mount it in, so I need two adapters anyway.
 

Malc

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Out of interest have you got a link to the Adapter you bought, You can get away with shorting the green wire ( /PS_ON ) to ground, Use a short length of wire ( Or paper clip ) and bridge the green wire and next door black wire together, This will turn the power supply on.

Note: later ATX psu's did not have the -5V line required by some isa cards, See here for the ATX power pinouts.
 

Malc

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Yes it appears so, With this adapter plugged in to the PSU but not connected to a motherboard, Have you got a couple of good known working IDE hard drives you can connect up to the psu to see if the drives power up.
 

Stone

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But without a motherboard the floppies just lay dead. They don't seek until they are initialized, and even then not without the aid of a FDD controller.
 
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