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63.5 watt PSU with a hard drive in an XT?

M

Mike Chambers

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Sep 2, 2006
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the power supply in my XT died, and i replaced it with a spare 63.5 watt supply originally from a 5150. i was wondering, do you think my XT might try to draw too much power for that thing? i turned it on briefly, and it booted okay with it but here's what i've got in there:

8087 coprocessor, 30 MB MFM drive, sound blaster pro 2.0, NE1000 ethernet, VGA card and an original full-height 360 KB floppy drive.

i wouldn't want to ruin my last spare... opinions on this?
 
Unless you really need to use the XT, my opinion would be just to get the 135 repaired and wait.

Just an opinion though.
 
i'm not really sure how to go about fixing the other one, but one idea that crossed my mind was gutting it and see if i can work the guts from a newer 200 or 250 AT-style PSU into it. i wonder how well it would fit, as far as mounting the board in there.
 
Check if there is a TV and Radio repair shop around, many repairs on those is to fix the power supply. Similar technology (usually the capacitors have gone bad).
 
Mike Chambers said:
one idea that crossed my mind was gutting it and see if i can work the guts from a newer 200 or 250 AT-style PSU into it. i wonder how well it would fit, as far as mounting the board in there.
Click to expand...

I've done this with the board from an ATX PSU. The board is too small to fit the standoffs in the PSU box but I just screwed in one corner and used some plastic spacers I found in my junk box on two of the other corners. It's not perfect but it's secure enough to do the job.
 
I believe those PSUs were made to shut down if the input or output was beyond a certain spec. Also Chuck's word is good in these matters. :)

I'd be tempted to get the other one fixed. It can't be that hard, or expensive. However, to help figure this out I just did some measurements on my PC which has only one full height FD. When you turn it on it goes to, and stays at, about 0.47 A (55W) until the drive kicks in and then it peaks at 0.56 A (65.6W) while that is spinning. That seems like quite a lot, but I suspect those PSUs were very conservatively rated.
 
Mike Chambers said:
i'm not really sure how to go about fixing the other one, but one idea that crossed my mind was gutting it and see if i can work the guts from a newer 200 or 250 AT-style PSU into it. i wonder how well it would fit, as far as mounting the board in there.
Click to expand...
http://www.vintage-computer.com/vcforum/showthread.php?27392-ATX-power-supply-guts-in-a-XT-power-supply-box

So one point is to make sure the vertical spacing is ok, especially where the fan is.
Footprints are smaller, but the newer PSU's often have a high heatsink.
 
Bear in mind ATX has no -12V. Actual AT PSUs seem hard to come by now though.

I have a 5150 that clearly has had an st-251-1 in it for many years (at least since 1991, judging by the private school financial accounts that were on it when I aquired it) which works fine. But the spin-up draw at 30W must be pushing the PSU right to the edge.
 
Not from experience but from stories and discussions I've always heard the 5150 power supply isn't made to handle the load of a hard drive. I'm sure it can but if it's under heavy utilization it may just zap the supply as well. I'm surprised from the repair comment though, I would think like most TVs and other electronics, the repair price typically throttles the cost of a used item. I would think the cost of repairing the PS would be close to buying another working XT, but that's my guess. If it was $10-20 and honest (since it's probably a bad cap or fuse component) for someone else to fix it then sure it'd be good. Otherwise perhaps scour local CLs for similar systems for parts.
 
MikeS said:
The -12V is still available, it's the -5V (for the old DRAM chips) that's gone.
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Geez, MikeS, you're been right-on all week long but as much as I hate to say it, your string has finally come to an end. :) If you look at the ATX pinouts you can see that the -5V is still there. Furthermore, I Just took a reading at the white wire on the cable of one of my ATX PSes and it was -4.97V. Some of them may not have it -- but some surely do.
 
It depends largely upon what you're using for a hard drive. If you're running an XTIDE with a CF card on it, you're good, even with an otherwise loaded system.

If you're running a 3.5" IDE, you're probably okay. If you're running a legacy MFM/RLL controller with a Maxtor XT1140, good luck with that. Note that if a drive puts too much drain on the PSU, the likelihood is that the overcurrent will be tripped the moment that you flip the big red switch. The big current draw on a hard disk is at power-up, when the drive is just starting to spin up. Once the platters are up to speed, it takes very little in the way of power to keep them that way. I recall that there were some over-loaded systems that required the power to be cycled a few times until the hard drive spindle acquired some momentum, then all was well.

Same goes for floppy drives. If you're using 3½" floppies, no sweat--if they draw anything at all from the +12, it's minimal. Half-height 5¼" drives, ditto. Full-height 5¼" drives tend to be more power-hungry.
 
Stone said:
Geez, MikeS, you're been right-on all week long but as much as I hate to say it, your string has finally come to an end. :) If you look at the ATX pinouts you can see that the -5V is still there. Furthermore, I Just took a reading at the white wire on the cable of one of my ATX PSes and it was -4.97V. Some of them may not have it -- but some surely do.
Click to expand...

Sorry my mistake re -12V, as said -5V was what I was thinking of, I thought it was dropped years ago (ATX 1.something I thought).
 
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