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This thread might be better suited for the "Vintage Computer Software" forum. Maybe some mod/admin could move it?

Yeah, it is definitely skewed on that particular picture. I just wanted to show the chip with the socket.

I see! Good to know that it is supposed to work, at least. Would have been annoying if I had bought a completely incompatible FPU.

Is there a good utility for modern windows (10 preferably) that can be used with a USB compact flash drive to determine the geometry (sectors, heads and cylinders) of a CF card? I have tried using biosdrvs and ideinfo on my vintage 386 system (using a cf->ide adapter attached to the i/o card)...

Yes exactly. I looked closely to make sure the odd corner was facing the right direction. Whenever I try to push it down properly into the slot, I push a corner down too deep into it, with the rest of the FPU sticking up somewhat instead.

I bought a [387 FPU] off Ebay for my new 386 system and was glad to find that it had arrived in my mailbox today. However, when trying to place it in the slot of my motherboard, I can not get it to fit, no matter how much i try. It seems like it should work but like it is just ever so slightly...

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

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

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.

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...

UPDATE: Okay, this is quite a head-scratcher. I switched out the two 4MB SIMM cards, replacing them with two 1MB SIMMs from my 286 mobo. Same A20 error as before and - here is the kicker - with /M:1, DOS reports the same unreliability error on the exact same address (00100000h). EDIT: Could...

MS-DOS 6.22 reports the exact same A20 error. EDIT: Running HIMEM.SYS /M:1 in CONFIG.SYS sort of works at first, and then reports the following (translated from Swedish):

I found [this] article through googling, written by someone also using an AM386SX processor, who also experienced the same A20 error. This seems to strengthen the case for faulty RAM being the villain of this drama.

Interesting! I will try to look up the specific A20 stipulations for the chipset in question. What I am starting to think is that perhaps someone who had this board before replaced a failty bios IC, but the replacement was of an older version of AMI BIOS that lacks options for regulating A20...

Noted! And no, I am not absolutely sure.

I got the same type of A20 error with FreeDOS, for what it is worth. I tried all variants between machine:1 and machine:16. Several of them reported A20 handler working, but no other software (HIMEM, Emm386, CheckitPro SysInfo etc) reported controlled A20 gate. Ah, good call! Did not know that.

Fair enough! Thank you!

Ok, so no point in trying the 286 keyboard controller displayed in the image above?

I see. Which IC on the motherboard is the keyboard controller? EDIT: Ah, the one between the IC with the white-yellowish AMI sticker and the ISA ports? I do have a keyboard controller chip on my faulty 286 board. I could swap the 386 one for that?

I switched the seats of the SIMM modules, thinking they might be in the wrong bank, but that proved to be false (loud beeps indicating that their new home wasn't suitable). Also, as indicated by MindWalker in [another thread], [this] seems to be a better bet for correct motherboard ID. I...