XT Power supply failed...

[modem7]

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.

'Dead' gives the wrong impression. A floppy drive will be drawing power even when not connected to a controller.

Different drives will draw different amounts of power, and different switch-mode power supplies will have different requirements as to start-up loading.

In fact, part of my 'Minimum Diagnostic Configuration' procedure (specifically the page [here]) for the IBM 5150 relies on the fact that a single Tandon TM100 floppy drive is known to present enough of a start-up load for the IBM 63 watt power supply.

It is aways going to be a case-by-case thing.

I was thinking two floppies might add additional loading in case the hard drive alone wasn't enough.

Well, they will add additional loading, but there is still the chance that the total start-up load will not be enough for your particular power supply.
It is just something to keep in the back of your mind.

 

[Al Hartman]

Yup. Just tried it, but it didn't matter.

I found an AT 300 watt supply at Newegg for $16.99, but it's not a drop-in replacement for an XT.

http://www.ebay.com/itm/Athena-Powe...-/301243532027?pt=PCA_UPS&hash=item46238382fb

I might order one and swap the internals with the dead unit. I have to crack open the dead unit in the morning and see if it looks like I can do it.

 

[k2x4b524[]

would it not have been easier, maybe cheaper, to source a XT power supply?

 

[Al Hartman]

Used XT supplies sell from $79.95 to $99.95+ on eBay.

It's not cheaper.

 

[modem7]

This is the cable I bought.

View attachment 20441

The arrangement of P8/P9 on the 5160 motherboard differs to the arrangement of P8/P9 shown in your photo of the adapter.
Are you aware of that?
The 5150/5160 arrangement is shown below (easily remembered as 'blacks together').

 

[Malc]

Yup. Just tried it, but it didn't matter.

It might be worth trying it without the adapter cable, Bridge the green wire to ground at the connector from the PSU, Just in case you got a duff adapter cable, Though like modem7 said it may be that the load is not enough for that particular psu.

..... I have to crack open the dead unit in the morning and see if it looks like I can do it.

Have a good look for anything obvious ie: burn marks, bulging caps etc, Good light and a magnifying glass is a necessity for me!.

 

[Al Hartman]

I know this ATX supply is good. It works to power an ATX logic board. I'm going to wait until I get the other cable before deciding what to do next.

 

[Al Hartman]

Got the power supply adapter so I could substitute an ATX supply temporarily for the 5160/XT style power supply that I killed. The 5150 PC powers up and works. It appears to be undamaged.

I had removed the board from the case to repair the speaker connector which had broken, and put a real jumper in place of the piece of wire I was using to enable 640k. 640k is recognized and speaker beeps.

I was able to successfully program the BIOS on the two Sergey 8-bit FDC boards. I have to test them later when I make up the cable. I may just throw a 3.5" cable and test with a 3.5" drive until I can find my IDC 34 pin connectors to crimp on.

Still waiting for the parts to finish the serial ports on the boards (square RS-232 chip, and de-9 connector.) I'll use Check-it with a loop-back plug to test the serial ports.

Feeling better that I didn't kill the PC motherboard. I was pretty sure I hadn't, but it's a relief to be sure.

 

[Al Hartman]

Found a 5150 230watt supply on eBay (a clone, I'd guess) on eBay for $30.00, so I ordered it.

I'll fix the damaged one someday, and use it as a spare.

Now, I can button up the 5150 in it's case and put it aside for awhile.