Help! Compaq Portable Plus suddenly died

[Oswald]

Gary, I have the rectifiers out now (there's a second obscured by the cluster of 4 big capacitors in the picture).

On both I think I was able to verify one-way conductivity between the two ~'s and +, and inverted one-way conductivity between the ~'s and -. My multimeter read between 520-550 every time, and the values seem to fluctuate a little. I also measured one-way conductivity between + and - between 1270-1300.

How does that sound?

 

[Gary C]

That sounds ok, which is a shame as that would have been too easy.

 

[Gary C]

Probably need to find someone with the SAMS photofact document to get a circuit diagram.

It could be those black disk like devices which one is probably a protective device and shorts the supply on overvoltage. One will be wired across the two mains inputs (ie across ~ and ~ at the rectifier) and should be open circuit when removed.

But this is shooting a bit in the dark.

You could try and draw out the circuit from the mains input as far as possible.

I take it if you measure resistance across the mains input, you get a dead short ?

 

[Gary C]

Actually, it would probably be easier to fit a small Meanwell PSU into the original case. They aren't too expensive and are a lot smaller than the original supplies.

When you connected up the ATX, was it +12, +5 & -12 ?

 

[Oswald]

I´ll order

Actually, it would probably be easier to fit a small Meanwell PSU into the original case. They aren't too expensive and are a lot smaller than the original supplies.

When you connected up the ATX, was it +12, +5 & -12 ?

Those and -5. I'm open to replacing the factory supply, would you recommend any supply in particular? I was thinking I might use a picoPSU, but I've heard they might not be the best choice for the Portable.

I'd like to fix the factory supply, but I'm really not an expert in electronics or troubleshooting. I'll gladly try out any recommendations or suggestions anyone here has, if I can.

Is this the mains input? This is where the blue and brown wires from the wall plug in, and where the fan plugs in, each connector has just two prongs. Do I have to solder the rectifiers back in to measure the resistance? Also, I still have the PSU totally out of the Portable, can I go on with the test? And just to verify, that's red multimeter lead to where the brown lead plugs into the Compaq, and black multimeter lead to where the blue lead plugs in, right?

Sorry for all the questions, I just want to be sure I don't mess up and make things worse

 

[Gary C]

I think we need a drawing as I am worried we might get lost with things.

The rectifier checks you did with them out of circuit showed they were fine, so its something else and its going to be hard to remote diagnose without a diagram.

The meanwell RQ-125B PSU gives +/-5V and +/- 12V and might fit ? but are £70

MEAN WELL Switching Power Supply, RQ-125B, ±5 V dc, ±12 V dc, 1 A, 4.5 A, 11 A, 500 mA, 120W, Quad Output, 176 → | RS

uk.rs-online.com

We really need someone with the drawing !

Anyone ?

 

[Oswald]

Update: I just found a shorted tant on the PSU. I've replaced it but I need to run off to get a new fuse (or two) before I can test it. It's possible to test out of machine, right?

Gary, does that PSU have a PWR good signal? The Portable needs one. I saw someone else use a MPQ-200B, but apparently the PWR good signal was being dragged down under higher loads and forcing the computer to reset. He apparently fixed the problem with a TTL chip.

Compaq Portable - Old Crap Vintage Computing

Compaq Portable is an early portable computer which was one of the first IBM PC compatible systems.

oldcrap.org

 

[Gary C]

Fingers crossed

 

[Oswald]

Update: I ended up just buying a used compaq portable PSU on eBay. Works fine