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Power supply from Compaq Deskpro model 1 (8086) not working

dhau

dhau

Experienced Member
Joined
Feb 13, 2018
Messages
323
Location
Toronto, ON, Canada
I bought a Compaq Deskpro model 1. It is in good cosmetic condition, but doesn't turn on. I checked the fuse in power supply and it was blown. I removed power supply from the computer, replaced the fuse, turned it on, and it blew the new fuse again.

Any advise what to look for? Should I replace tantalum capacitors? Anything else I can check?
 
Hey guys, what is the fuse spec that I should use with this power supply? It is 200W, 110V, so I assume I need 2.5A or 3A @ 110V fuse. I can only find 250V rated fuses online, does it mean I should look for like 1A or 1.5A @ 250V fuses?
 
If the Deskpro 8086 is anything like the 386, you may wish to give the tantalum caps a one-over. My 386 had some blowouts on the motherboard I had to sort out before it came to life.
 
MrArgent said:
If the Deskpro 8086 is anything like the 386, you may wish to give the tantalum caps a one-over. My 386 had some blowouts on the motherboard I had to sort out before it came to life.
Click to expand...

Thanks, for sure, I'll get to that.

But for now, the PSU blows the fuses without any load, i.e. disconnected from the motherboard. I don't think it's normal.

I cleaned it thoroughly as it was very dusty inside, but I'm out of fuses to try it out again :)
 
Again, the most likely culprit (even in the P/S) would be the capacitors (assuming it hasn't suffered something like a lightning hit). If you're comfortable with taking it apart, and know how to use a multimeter, then that likely will go a long way in successfully repairing the machine...
 
Not in the fix it vein, but there are two different Deskpro power supplies for sale on eBay. One is 55 + 23 shipping, the other is 68 + 15 shipping.
 
Casey said:
Not in the fix it vein, but there are two different Deskpro power supplies for sale on eBay. One is 55 + 23 shipping, the other is 68 + 15 shipping.
Click to expand...

Thank you for the hint! It is good to know there are still spare parts available. I tested my Deskpro (model 1 8086) with the power supply from Deskpro 286 (model 2550) and it lights up, the fuse doesn't get blown, the light goes green in front, but nothing on speaker or display.

I'll have to use diagnostic card on this PC and if nothing there, a diagnostic BIOS as per this.
 
dhau said:
Thank you for the hint! It is good to know there are still spare parts available. I tested my Deskpro (model 1 8086) with the power supply from Deskpro 286 (model 2550) and it lights up, the fuse doesn't get blown, the light goes green in front, but nothing on speaker or display.
Click to expand...

Hmmm. That matches what happened to me. I bought a surplus Deskpro 8086 with a known bad power supply. Dropped in a working Deskpro 286 p/s and blew a capacitor. I took the advice from someone here and just clipped that puppy off. I tried again, but no boot. The lights on the keyboard blink on & off, and the p/s fan runs, but that's it. Time to dig out my own boot card, then.
 
MissArgent said:
If the Deskpro 8086 is anything like the 386, you may wish to give the tantalum caps a one-over. My 386 had some blowouts on the motherboard I had to sort out before it came to life.
Click to expand...
Do you have a caps list for the 386 version? This is my CPU and PSU.
 

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This is pasted verbatim from my text file, but here we go

Code: 
Mrs. Argent's Cap Counter!
(Augh)

VARIETY 1: Tantalum, Large, Orange (10uF 15V)
............... -> 16 caps

VARIETY 2: Ceramic,  yellow, larger than V3 (473)
................................................................................. -> 81 Caps

VARIETY 3: Ceramic, yellow, slightly smaller than V2 (103 ESM)
. -> 1 Cap (but it's about the same size as V4. Augh)

VARIETY 4: Ceramic, Yellow, Nearly identical to V3 (102 CSM)
.......... -> 10 Caps

VARIETY 5: Ceramic, Yet another tiny indistinct yellow cap. Bastard. (470 ASK)
... -> 3 Caps

VARIETY 6: Ceramic, Yet more indistinct yellow. This one is the smallest. (100)
. -> 1 Cap (C100)

VARIETY 7: Guess: Ceramic Indistinct yellow. (180)
. -> 1 Cap (C117)

TOTAL ... EST.  113
BOARD ... COUNT 117 ???
[code]

I didn't tally the PSU, but replacing the tantalums was the big thing in my case. Best of luck!
 
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