A20 issues with my 386

[boggit]

Some pictures of the motherboard:

[Back]

[Jumpers one and two. Also proof that Bank 1 is the one closest to the edge of the mobo]

[Front overview]

[Close-up of the upper jumpers]

[RAM sockets. No funny business here, it seems]

EDIT: After re-installing the motherboard into the case and booting it up, HIMEM.SYS/A20 now miraculously works.

I don't know what I did or how I did it, but thanks to everyone who followed me on this weird journey.

 

[krebizfan]

Glad to see you got it worked out.

 

[boggit]

When removing the motherboard from the case, I accidentally pricked a finger on some sharp PCB pins, resulting in some blood on the motherboard. It might very well have been the blood sacrifice that got the thing working.

 

[resman]

Be careful, these things don't always end well: https://en.wikipedia.org/wiki/The_Mangler

 

[wrljet]

When removing the motherboard from the case, I accidentally pricked a finger on some sharp PCB pins, resulting in some blood on the motherboard. It might very well have been the blood sacrifice that got the thing working.

You should clean that off well. Blood is corrosive.

 

[Endersending]

I noticed the first picture of ram has parity chips (the IC that is vertical on right side of ram stick). You said you tried different ram, have you tried ram without the parity chip? I also know 386's can be picky about memory density, so trying different ram stick with different chip configurations can sometimes help solve a problem like this.
The other thing I would check is corrosion under something, a via or solder connection. sometimes it takes looking the board over a million times before you notice something you didn't see before. Also set your bios settings to factory defaults if you have not tried.
good luck

 

[boggit]

You should clean that off well. Blood is corrosive.

I used q-tips to remove any hint of blood.

 

[boggit]

I noticed the first picture of ram has parity chips (the IC that is vertical on right side of ram stick). You said you tried different ram, have you tried ram without the parity chip? I also know 386's can be picky about memory density, so trying different ram stick with different chip configurations can sometimes help solve a problem like this.
The other thing I would check is corrosion under something, a via or solder connection. sometimes it takes looking the board over a million times before you notice something you didn't see before. Also set your bios settings to factory defaults if you have not tried.
good luck

Thank you but as I wrote above, the problem has been solved.