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COMPAQ Power Supply

J

Jtterbug

Experienced Member
Joined
Sep 13, 2010
Messages
158
Location
Pacific NW
Hello,
I have 2 questions;
1. What are some Common Culprits That prevent a COMPAQ from working other than the PS?
2. What does the power supply look like?

I can give a run-down if anyone needs/wants it.
 
Do you mean not turning on?

It could be a number of things that keep it from powering on. A faulty power switch/button. Swollen/busted capacitors can cause it to momentarily turn on, then off. Something could be shorting out somewhere. Is the computer completely dead when you press the power button, or are there any sounds (electrical noises) coming from the power supply.

And is this a laptop or desktop. Some more specifications would be helpful.
 
It is a COMPAQ Portable No.1.
The fan runs, and sometimes the tube lights up at the base. A little LED on the Motherboard lights up for 1/20 of a second.
 
Something could be drawing too much power and causing everything to shut off. Does the fan stay running after the motherboard light goes off? Does it have a hard drive?
 
Had this exact same issue on my machine. Turned out to be the floppy controller board. Try pulling out any non-essential cards & disconnecting drives
 
It does have a HDD.

I shall try unplugging everything but the Video card.

The fan does continue to run.

Where is the PS? Is it the board right next to the tube to the left (Looking at it as if using.)?

That last question must sound silly, but I just want to make sure.
 
If I remember correctly, the fan runs off of mains (120v), so as long as the fuse isn't blown, it turns on..

If your looking at the machine from the back (back closest to you), the PS is tucked up to the right of the monitor. I had to remove the monitor to get at it.

As has been suggested unplug all drives,, pull all cards, unplug the 12v supply to the monitor, and unplug the motherboard power connector.

Then power it on, and check that the power supply is putting out 12v and 5v on the floppy power connectors. If it does, then start by plugging things in the reverse order, motherboard first, monitor, cards, drives, until its stops working again.

Cheers, Joe
 
Well, I unplugged the Floppy drives, all the cards and the Screen, and now the little light on the motherboard stay lit for about 1/2 of a second.

How do I remove the screen?
 
I had the same issue on mine also, upon closer inspection of the psu board (which is a pain to get out!), I found myself an exploded cap.

The CRT comes out as a whole cage. There are screws both on the top and bottom. be careful, the power supply and brightness wiring come out of the bottom and are well attached to the chassis. The white wires that go into the crt cage are what will keep it in, unplug that. It's keyed, so you can't get it back on backwards.
 
IIRC, There are 2 bolts that have nuts on the board, on the fan side, top and bottom. Once the nuts are removed, slide the board towards the back. You will need to disconnect the wiring first.

To get to the bottom one, I rigged up a tool so I wouldn't have to take anything else out, but taking the CRT cage out will get you better access.
 
Well, I got it out and.....NOTTHING! All the caps look perfect! I just don't get it. Do I short them out and test them with an ohm meter? Or is this another problem? Is it beyond repair?
 
Jtterbug said:
Well, I got it out and.....NOTTHING! All the caps look perfect! I just don't get it. Do I short them out and test them with an ohm meter? Or is this another problem? Is it beyond repair?
Click to expand...

The Tantalums can look OK and still be shorting out. Try putting your multimeter probes across the tantalums that are close to where the power supply connects to the motherboard and see if you get any readings close to '0'.

The fact that the red led on the motherboard comes on and then goes off indicates that the power supply is starting up and (possibly) shutting down from something drawing too much current.
 
I wish I had caught you sooner. I did the power test with nothing connected to the PSU; Normal. With Motherboard; Starts at 14v and falls like a rock to .01v.

What does this indicate?
 
There's a short somewhere. Check out the motherboard very closely, and the wiring in between. Could still be a psu issue (adding load causes the issue).
 
I am so sorry, I skipped right over it too.

If I don't understand how to do it I'll ask for more detail.
 
I got it out, CB3 and CB4 have no resistance, this is abnormal compared to the rest. If this is in the manual, sorry, but are they intended to be like that?
 
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