ATX power supply guts in a XT power supply box

[reenigne]

Has anyone here successfully modified an XT power supply to use the innards of an ATX power supply? My XT's power supply stopped working (no voltage on the output lines, although it does seem to work on the first power-up after discharging the high-voltage capacitors). I figure a more modern supply is likely to be more reliable, but the holes in the case won't be in the right places and I want to keep the big red switch, so I'm going to attempt a transplant.

I think I'll be okay soldering the XT's power connector to the ATX power supply board, wiring up the switch/sockets and grounding the "power on" line, but one thing I'm not sure about is how to mount the board in the larger XT PSU case, since the standoffs won't be in the right places. I'm considering making standoffs by putting some blobs of hot glue in the appropriate spots and driving self-tapping screws into them just so that it won't rattle around or short against the case, but I wondered if there was a better way (especially if it doesn't involve drilling holes in metal - I don't think I have the right equipment for that).

 

[Jorg]

I just did that two weeks ago. I'm by no means an expert at it, but if you want to know what I ran in to (just a few things), fire away.

Pics are here - they are in reverse order

http://s1083.photobucket.com/albums/j387/stufffs/other/

Best try to find an ATX supply with relatively low heatsinks, there is not much place for the fan on top (which is 220V in the original psu, by the way).
I couldn't keep that as it is 2" high.

Standoffs, I used one original mounting, one non-fixed motherboard stand-off, and for two I drilled a 3mm hole in the bottom and used a 3 mm bolt with nuts as spacers- fixed the nuts with glue (don't want them to come off and wander around..)

Warning:
I seldomly open high voltage stuff. I know my limitations.
So I did take a *lot* of precautions in this case before opening these things up.
Be aware of the risks. If you are not, ask around first or just stay away.

 

[eeguru]

I recently did the same thing with my 386 however I used a new AT switching power supply. Believe it or not they are still made and I bought one off the shelf at Fry's. It has the advantage of everything being wired correctly already so there is minimal soldering. You just slip the clips off the relatively newer included spring loaded push switch and onto the 'big red switch' in the old PSU enclosure. I had to move/solder wires over to the power cord receptacles in the old enclosure and solder in the fan leads. But that was it. I used the PCB from the new PSU as a template to score and drill holes on the under side of the old PSU case and then tapped them from the inside, counter-sunk the outside, and attached new stand-offs. The new AT PSU had the P8/P9 connectors already so no soldering was required in that respect.

Ran much cooler than the old so I could run the fan at a lower RPM. After also switching out the 2 old RLL HDs for a single CF card, the machine is 1000x quieter; which I almost don't like - almost!

 

[reenigne]

Thanks! Jorg, don't your bolt standoffs prevent the PSU from sitting flush with the bottom of the case? Or do they go through the case as well?

 

[Jorg]

Thanks! Jorg, don't your bolt standoffs prevent the PSU from sitting flush with the bottom of the case? Or do they go through the case as well?

For the bolts, I drilled a l hole just in the PSU case.
Bolts are 3 mm with a head like this (not sure what its called in english):

I widened the hole a bit so they just stick out about 0,5 mm on the bottom of the PSU case.
You will notice the psu case slits in the pc case on two 'hooks'.
That is not a 100% thight fit, enough room for a bolt head hardly sticking out.

On the inside, I used a

to make sure its stable.

As for ATX -> AT, I used this adapter.

If needed, you could use the big red switch to switch the grey/black wires.
I decided to use the BRS to switch mains (it is rated for that), and permanently connect the grey/black.
This has the advantage that I can still remove the adapter easily when I want to put an ATX board in the case.

Also, see JDT's post http://www.vintage-computer.com/vcforum/showthread.php?10897-Rebuilding-PSU&p=62087#post62087

In the end, the only serious thing I bumped into was the height of the heatsinks combined with the height of the fan, and the vertical space in the psu case.
A 3/4" high 8cm fan would have been ideal.

In the end I ended up cutting some things off the 1 " high fan that came with the ATX psu, so its gets 'close to the ceiling' (there are some protruding points where the screws are).
If you find a 'low profile' ATX psu, that would be the best.
My feeling is also that the air flow is not that huge due to the place of the fan in the case, so I think its better not to install a big power ATX PSU anyway.
I was looking for a 150W one, but ended up with 235W.