There is no green wire to ground trick like on ATX psus. AT psus are sending power directly into the computer. The on/off switch outputs directly the 110v/220v into the PSU. When the psu is powered on, the computer starts up, there is no switch for the motherboard. If the psu doesn't start up, well there must be a short circuit inside or something else that makes it unable to start up

Is there a "Dallas" ic on the board ? This is an integrated RTC clock that also contains a battery

Yes yes, there is a "Dallas" time clock chip, so do I have to unweld it ?

You don't need to fit your 486's PSU into the 386's case.
Do it dirty, just to see if the motherboard works: Unplug everything from the 486. Remove the 386 motherboard from the case and place it (carefully, mind insulation) somewhere where the cables can reach it (usually on top of the case or on some books/box on the side) . Then turn it on using the 486's switch.

I can't, the cables of those PSUs manufactured into the cases are "just enough" to reach the socket in there, even the AT cable of the 486's PSU is stretching enough to reach the socket in there (might be all rolled and stopped beneath the motherboard or something)...

What does 'not power on' mean in your terms? Dead? Fan running but no display?

Does it power up with the mainboard unplugged and only the harddisk connected...
Have a multimeter?

unplug 386 from psu and then press the power button and find out if that psu works

For the DALLAS chips, you can find datasheets online, but those are tricky SOBs. I specifically bought a board without one for the sole reason of NOT having to deal with them. If you want to do it the right way, pick up a 50 cent drop in replacement RTC chip, unsolder the chip (Cheap soldering iron and some copper desolder wick will do) and for your peace of mind, throw a socket in there, then the chip.

Not entirely sure what you mean by "Jump start" if you mean shorting the pins to power the machine on, the PSU has a power switch attached to it. But if you think it's the RTC, they are easy enough to replace. As I said, socket it, I am sorta annoyed at board manufacturers for socketing everything BUT the RTC. Heck my board has it's RTC on a socket, it's also got an external battery (Not a DALLAS type RTC)

My father even tried to solder in an AA battery somehow, but it did nothing at all apparently...

By "not powering on" I mean that I press the button and nothing at all happens or, better, something happens for like a second and then stops completely.

I'll make a quick video and post further information once I bring that PC here.

Not sure how he would solder in an AA battery. Keep in mind CMOS voltage ranges from 3-4VDC with 3 AAs (GREAT if you have 1.2v rechargable AAs) under load, it will be fine. Not sure if the Dallas RTCs have CMOS power in to bypass the battery, probably don't. There probably is a way around it, but your best bet is to just throw in a new RTC if you think that's the issue. The battery is self contained in the RTC, and once it's dead, your not going to replace the battery ever.

It doesn't seem like a RTC in my opinion, but I've never dealt with a 386, so maybe it is.

As it's an Epson, and some of their older systems have rather exotic proprietary main boards, it could be something else altogether. Does the system even have a BIOS in which the settings are stored, or does it use little switches behind a little panel on the front for its settings?

candle_86 wrote:

unplug 386 from psu and then press the power button and find out if that psu works

Did you do what candle_86 suggested? Does the PSU work with everything unplugged or still it "stops completely"?

Elia1995 wrote:

My father even tried to solder in an AA battery somehow, but it did nothing at all apparently....

Why, and where?

Elia1995 wrote:

By "not powering on" I mean that I press the button and nothing at all happens or, better, something happens for like a second and then stops completely.

Three options:
The power supply is broken and won't stay on to protect itself and other equipment.
Something else is broken, draws too much current and power supply shuts down to protect itself.
You have unplugged something and the power supply has too little load, goes out of regulation and shuts itself down. Not all PSUs want to start up without load, so you should at least have a motherboard or 1-2 hard drives as a dummy load.

Can a crappy Avance Logic ISA sound card "draw too much current" and the PSU can't handle it ?
Because that's the only actual thing I did... I just added an ISA sound card to "level this PC up and get rid of that noisy PC speaker once for all"... but I can't think it's the cause... after all why would they put in a motherboard with ISA slots and a PSU that can't handle them ?

Elia1995 wrote:

Can a crappy Avance Logic ISA sound card "draw too much current" and the PSU can't handle it ?
Because that's the only actual thing I did... I just added an ISA sound card to "level this PC up and get rid of that noisy PC speaker once for all"... but I can't think it's the cause... after all why would they put in a motherboard with ISA slots and a PSU that can't handle them ?

If it's not broken, it can't draw too much current.
If it is broken, or inserted incorrectly into ISA slot, then there might be a shortcut.

Elia1995 wrote:

Can a crappy Avance Logic ISA sound card "draw too much current" and the PSU can't handle it ?
Because that's the only actual thing I did... I just added an ISA sound card to "level this PC up and get rid of that noisy PC speaker once for all"... but I can't think it's the cause... after all why would they put in a motherboard with ISA slots and a PSU that can't handle them ?

First rule, take out everything you DON'T need out of the board. There should honestly be nothing in there aside from a video card (If you do not have onboard video) the minimal amount of memory needed in one SIMM slot, and a keyboard. There should be no M/I/O or sound cards inserted.

You still haven't figured out if it's the PSU not turning on. Does it power other boards? Can you test to see if it's within an acceptable voltage margin on each line?

You can also try a POST card if you own one, they display numbers telling you what's going on in the boot process.

These boards should work with a dead RTC, I see no reason why they shouldn't, but in the event this board is just designed poorly and doesn't work without the RTC, transplant one from another board for testing, or buy a new RTC and a socket (Make sure to socket it, it will save you and any future owners a load of trouble).

Maybe it would also help to check whether the manual for this computer is available on the web, e.g. on this site: https://www.manualslib.com/brand/epson/desktop.html

Ampera wrote:

First rule, take out everything you DON'T need out of the board. There should honestly be nothing in there aside from a video ca […]
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Elia1995 wrote:

Can a crappy Avance Logic ISA sound card "draw too much current" and the PSU can't handle it ?
Because that's the only actual thing I did... I just added an ISA sound card to "level this PC up and get rid of that noisy PC speaker once for all"... but I can't think it's the cause... after all why would they put in a motherboard with ISA slots and a PSU that can't handle them ?

First rule, take out everything you DON'T need out of the board. There should honestly be nothing in there aside from a video card (If you do not have onboard video) the minimal amount of memory needed in one SIMM slot, and a keyboard. There should be no M/I/O or sound cards inserted.

You still haven't figured out if it's the PSU not turning on. Does it power other boards? Can you test to see if it's within an acceptable voltage margin on each line?

You can also try a POST card if you own one, they display numbers telling you what's going on in the boot process.

These boards should work with a dead RTC, I see no reason why they shouldn't, but in the event this board is just designed poorly and doesn't work without the RTC, transplant one from another board for testing, or buy a new RTC and a socket (Make sure to socket it, it will save you and any future owners a load of trouble).

For the RTC why not just battery mod it? I've done it before.

Seriously? The RTCs are probably cheaper than the CR2032, and with a socket you can just replace the RTC whenever you want.

Are you going to test the power supply before modifying the board or not?