My 386sx refuses to start in cold days

Question

My old computer refuses to start in cold days. So, in really hot days (about 40ºC / 104ºF ) or even hotter, this PC usually starts, but in cold days, it wont.

When the temperature is not in the "sweet-spot" the power light turns on for an half a second and then the computer turns off. But when it's really cold, not even the power light turns on, nor even a blink. Sometimes I use an Hair dryer, pointed directly to the PSU and that works great. 5 to 10 minutes is enough, depending on the ambient temperature. I think something is going wrong in my AT power supply.

I can't replace this PSU for another because it has a non-standard size and connectors to power the motherboard.

Does anybody have a clue about what it's failing in my PSU, so I can change that component (resistor, capacitor, ??, etc) and rock on with my 80386?

This is a Schneider EuroSX, manufactured between 1989 and 1991 (I guess)

PSU Info:

Inside PSU:

Answer 1

This is pretty old machine and electrolitic capacitors tend to decay with time. Have you considered replacing all of them?

Answer 2

I think something is going wrong in my AT power supply.

What brand and model of PC is it? If you tell us, you may get responses with sources for spare parts.

I can't replace this PSU for another because it has a non-standard size and connectors to power the motherboard.

You may not unwilling to replace it, but many other people can. PC power supplies have fairly standard outputs (+/-5V, +/-3.3V, +/-12V. Some of these have "gone away" in modern ATX 2.0+ specs (like -3.3V), but new power supplies are still on the market that meet the old specs.

I really don't understand the willingness to replace a PSU component and not the entire PSU. It is pretty easy to find out which pins produce the various volts and ground on your old PSU, and then move the non-standard connectors over to the new PSU.

Size is also not an issue. First of all, you can find new power supplies in any size, if you are willing to pay $50 or more for them. Second, the PSU need not reside inside the system case, nor does your system need to reside in its original system case.

Does anybody have a clue about what it's failing in my PSU, so I can change that component (resistor, capacitor, ??, etc) and rock on with my 80386?

Besides dried-out capacitors as Ivan mentioned, there may be a little crack in the circuit board or a bad solder joint, that needs to expand enough from heat to make contact. You may have an IC that is not temperature stable. The contacts between the PSU and the M/B may be corroded and need burnishing.

Please share with us the true constraints you are working under. You seem to be willing to use a soldering iron but not a voltmeter? Is the true constraint cost?