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Compaq Portable III Power Supply removal

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AndyO

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I have a Compaq Portable III which has suffered what appears to be a significant impact on the bottom corner where the power lead connects, and on the side-panel where the vents are for the power supply.

The bottom corner of the casing, and the PSU itself is deformed, but the main part of the damage is that the metal panel up the side of the PSU - the metal has holes for ventilation - has been pushed in as much as 3/4 inch along the 'top' (meaning along the edge of the PSU that runs close to the back panel.

I was able to disassemble the computer to the point where I can get at the whole PSU, where it looks like it's designed to simply slide out as a complete assembly.... but it doesn't budge, and there's no place where it appears I can exert any leverage or force.

It's possible that the PSU is jammed in place by the deformity, or that I have missed some screws that hold it in place, but I don't think that's the case.

Does anyone know if the PSU really does 'just' slide out, once the back panel and motherboard are removed? If I can source one, and can remove the damaged unit, I'd certainly want to get this back in working order, even if with superficial damage to the outer case.

Incidentally, the system doesn't power up - which is probably no surprise.

Any thoughts?
 
I haven't touched my Compaq Portable III in a while. I think there are some screws in the front bezel that you have to unscrew.
 
Apologies if this takes a while to post, but being a newbie, it has to wait for moderator approval (that is not a complaint!)

I couldn't see any screws from the front of the unit, but it would make sense that there should be something other than friction to keep the PSU in place!

I found what looks like the service manual for the 386 model, which has (mostly) the same structure, though a different motherboard, and that does indeed show 4 screws behind the plasma display. Since the models are structurally very similar, it makes sense the portable III would have them too.

Thanks!!!!

Next, I'll likely need a new PSU, so a further question would be: Given an impact that caused damage to the plastic casing, and the side of the PSU itself, is there anything else that may have been damaged by the physical shock? Hard to know for sure, I know, but what other problems ought I to be looking for if I can get it back into shape?
 
AndyO said:
Next, I'll likely need a new PSU....
Click to expand...

Replying to my own post... bad habit! But I have sourced a replacement PSU for the computer, and will undoubtedly discover in due course what else is wrong. I also have a second portable III which does power up, but won't boot because the CMOS battery is dead. I don't have a diagnostic disk, and no way I know of to create one - but with any luck I can make one good system at least. Hopefully two!
 
I got the Compaq booted after using the hard drive from the damaged system, and a newly-acquired diagnostic disk to set the drive type. It booted, the screen was good, and I was able to read and format a floppy.

Then it died. The power supply looks like it has failed. I switched out with the PSU from the other one, but that doesn't appear to drive the display - it remains dark, even as the system seems to be booting.

Two questions:

1. Is there anyone out there who can be recommended as a source of repair for the dead PSU?

2. Probably a very stupid question, but my memory is a bit of a black hole for the late 80s....if I was going to connect the portable to a monitor via the RGB connector on the rear panel, what cable would I need? I have VGA displays, and HDMI, but nothing I recall with a 9-pin RGB input.

I really do want to get this up and running - it's too cool to let it sit and be forgotten!
 
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It can be multiple things. The capacitors in these systems are 33 years old, and some of them may have either dried up or have leaked. I had a capacitor pop on my Portable III's screen control board 9 years ago. It didn't affect anything, but I wasn't able to use it properly due to me lifting a pad under a chip on the flexible cable when I attempted to repair it. I just bought another III system and pulled the (slightly screen-burned but otherwise fine) screen out of that. I got some nice replacement parts for it too.

Have you listened for a click when you turn on the power?
When you flip the power switch, there should be two quick additional clicks from inside the system. (That's an electrical relay clicking into place) If not, your power supply is not working correctly and not providing power. For systems like these, there is also a short test by the supply to see if the power has stabilized, then the power supply sends a signal down a wire called the "Power Good Signal", which turns on the motherboard.

Also, video from around this time followed the CGA standard. It used digital signals (off-or-on signal switches representing color and intensity), in a system called TTL (Transistor-Transistor Logic) to send the picture to a screen controller inside the monitor.
VGA is not the same. It uses analog signals, which doesn't follow an on-or-off pattern.

It's like trying to speak Morse Code to someone who only knows English by voice. If you want it to work like that, you need to get a screen that can handle those signals, or find a translator board. (i.e. CGA-EGA to VGA) They seem to be around on eBay.
 
The power supply is definitely dead - no click when turned on, and the red LED on the motherboard also doesn't light. No system activity of any kind. There was no sound or smoke though. I had transferred the floppy and hard drive - the entire cage - from one machine to this one, and it booted up perfectly, and ran for 10 or 15 minutes, allowing me to format a floppy, and check the directories on the HD. The screen was good, though the contrast pot was a bit noisy when adjusting it, but all working just fine. Then, while I was doing something else for 5 minutes, it went off.

I switched in the power supply from the other system, which is the one that had impact damage and hadn't worked, and it fired up, but the screen didn't come on. I suspect the second power supply isn't outputing the 200v for the screen, but that otherwise the system may well be working - hence being curious about connecting up an external monitor, is that is possible.

So, I may have two PSUs that need repairing. The dead one from this, otherwise probably working, computer, and the original which isn't powering the screen. I don't have any skills in this kind of work, so I'm thinking that if there's anyone, anywhere, who repairs old systems and can take a look, I'll mail at least the dead one off, while (hopefully) being able to use the system with an external monitor and the partially-working PSU that is now in it.
 
I wouldn't mail off any of them.

I had a dead Zenith laptop (The SuperSport kind) that had leaky and bad capacitors, and changing them out brought it back to life. Replacing them in the power supply may change your situation. Even though they seem fine on the outside, remember, these are 33 year-old capacitors. The rubber plug that seals the inside dries out, shrinks, and lets the liquid electrolyte inside dry up as well.
 
If I had any skills in electronics repair, or any equipment, I'd be happy to have a go, but without a Radio Shack to go to for parts, or a place in the house to work, it's not all that practical.

That said, the proposition of simply replacing components is not a bad one in slightly more conducive circumstances, because there really can't be much wrong with the PSU - it's just a circuit board populated with stuff after all!

And in the end, there isn't a whole lot of alternative choices to be made since I don't see a queue of technicians at the door offering their services!

There is one other question though:

As and when I am able to plug an external display into the computer, is there a setting I need to change? Absent documentation, I'm not sure if, for example, there's a DIP swi
 
There's a place called Mouser, where you can buy these items cheaply.

Digi-Key also sells electrical components, but they're a bit more expensive.

Also, I don't believe you need to change any settings. The inside of the back plate of the Portable III doesn't show anything important.
 
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