I've checked and PSU gives 5V onto PG pin. Acctually now PC speaker on motherboard seems to be alive, but instead of any beep sequence it just gives single beep tone without any breaks. It gives that tone, even when there are no POST codes on the POST card.

I still say it's either a memory or a CPU problem. Only one way to find out.
Did you test it before cleaning? Maybe it was damaged during the several hours process.

Miphee wrote on 2021-03-03, 10:18:

I still say it's either a memory or a CPU problem. Only one way to find out.
Did you test it before cleaning? Maybe it was damaged during the several hours process.

Well, it's my mistake but was too scared to power it up before. Most of the time I was cleaning the case and psu internals. All I did to Mb was sweep it with soft makeup brush .

Also, I have noticed that around some pins there is whitish goo ( Mostly around GPU chip). Is there any chance that this substance is a problem? Also sorry for pic quality but my microscope does not support making pictures.

Is it hard or soft? Just try cleaning with some alcohol.

I have the feeling that you are getting there. Some optimism!! 😀

Nexxen wrote on 2021-03-03, 14:35:

Is it hard or soft? Just try cleaning with some alcohol.

I have the feeling that you are getting there. Some optimism!! 😀

It's soft and hard to clean.

Now I got to the point where 98% of boot attempts I get the same post code ( sometimes with one continious bees, sometimes not). The code is 0504. 04 means that keyboard controller test is passed and 05 - Chipset initialized...DMA and interrupt controller disabled.

Try compressed air everywhere.
Wash it with some dish soap. Nothing will happen if you dry it. You can even put it in the over at 50°C for 15 minutes...

Could be dirt and probably loose joint.
You can use some fine tip + magnifying glass and check if all soldered pins are not moving.

Nexxen wrote on 2021-03-03, 19:33:

Try compressed air everywhere. Wash it with some dish soap. Nothing will happen if you dry it. You can even put it in the over a […]
Show full quote

Try compressed air everywhere.
Wash it with some dish soap. Nothing will happen if you dry it. You can even put it in the over at 50°C for 15 minutes...

Could be dirt and probably loose joint.
You can use some fine tip + magnifying glass and check if all soldered pins are not moving.

I'll try to inspect it with microscope. The olny oven I have is for food so I don't want to poison my family.

Bernkastel7734 wrote on 2021-03-03, 20:01:

Nexxen wrote on 2021-03-03, 19:33:

Try compressed air everywhere. Wash it with some dish soap. Nothing will happen if you dry it. You can even put it in the over a […]
Show full quote

Try compressed air everywhere.
Wash it with some dish soap. Nothing will happen if you dry it. You can even put it in the over at 50°C for 15 minutes...

Could be dirt and probably loose joint.
You can use some fine tip + magnifying glass and check if all soldered pins are not moving.

I'll try to inspect it with microscope. The olny oven I have is for food so I don't want to poison my family.

You don't have to bake it @350 °C 😀 ... Just enough to dry it off, or use a hairdrier.

Nexxen wrote on 2021-03-03, 19:33:

You don't have to bake it @350 °C 😀 ... Just enough to dry it off, or use a hairdrier.

Ohh, okay

Check if it beeps w/o BIOS chip, maybe it emits some random noise?

Quick update :
Got other 486 MB with the same 486DX-33. That board does boot up. Checked CPU from my Vectra, it didn't boot up. Checked that working 486 on Vectra MB, still no boot.

So the CPU from your Vectra doesn't work on your new mobo but the Vectra still doesn't work with the working dx-33 ?

Deksor wrote on 2021-03-05, 13:59:

So the CPU from your Vectra doesn't work on your new mobo but the Vectra still doesn't work with the working dx-33 ?

Yes

Also, I have noticed that this working one, does not have 'INTEL©1989' Marking on the bottom. Does that mean it's a counterfeit one?

Well, it was a quick adventure. My second 486 MB stopped booting up. Gyah.

Are you sure the hp vectra didn't kill the working CPU ?

Also are you sure you inserted the CPU properly in the socket ?

Deksor wrote on 2021-03-05, 17:34:

Are you sure the hp vectra didn't kill the working CPU ?

Also are you sure you inserted the CPU properly in the socket ?

It didn't, after checking in with Vectra, it booted once. It stopped after I connected HDD to it. And it's properly inserted.

Well I guess you can make a topic for that board too ^^