Long + 8 beeps = video card issues (missing or bad video card, or just bad contact).

The chips you seen in sockets are actually RAM chips. No 286 had cache as far as I know.

The empty socket take SIPP memory. They're identical to simm memory except they have a male connector instead.

You can actually replace the sipp sockets with simm socket for convenience.

Interesting thanks. The video card is a known good card. I suppose I can try another one? Would this board support a Trident VGA card?

Obviously it could be an issue communicating with the slot.

Thanks again!

Update

I have tested two different 16bit VGA cards and one 8bit EGA card. Same beeps. I also have the beeps when there is nothing plugged in. I see the correct voltages on the ISA slots.

Could you possibly confirm that what I hear means an issue with the video card?

Here you can play the sound file: www.cinematech.it/MyLinks/beep.mp3

Thank you a lot!

Beep Codes depend on the type of BIOS you have (Award, Phoenix, ...), but you dont know which one is installed.

But yes, its likely that its related to theVideo card. Maybe the board is jumpered for CGA/mono? I would try to switch all jumpers one after one and see if something changes...

I fixed it. One ISA pin was bent and touching an adjacent one.

Uff. I fixed two boards in 30 minutes. I was hoping they would keep me busy for a while...

Thanks for your help!!!

Good job ! This counts as "bad connection" to me 😀

Can you dump the bios so we can add it to UH19 (see my signature) ?

ahahah - point taken! 😀

Sure, I will do that later. Thank you again for your help!

Hi there

After washing the board, there seem to be an issue with the memory being recognised by the board. It only sees "one bank" (in the BIOS it says that only bank zero is enabled, 256KB) but memory count says 512KB. I tried moving around memory modules - and also only using one bank? - but I had no luck.

My main question is: what is enabling or disabling those banks? The chips themselves?

I also replaced all the electrolytic caps on that board.

I kind of remember having issues with that board when it first booted up, where the memory was not correctly recognised and it took a few reboots - and BIOS write - to correct.

Any ideas is appreciated! Thanks

One memory chip is 256kB x 4 bit, so you should get 8 x 256kB x 4 bit = 1MB
Maybe some memory chips are broken ? I can't see any jumpers for memory configuration (there are jumpers for selecting memory bank on my 286 SCAMP board).
Unfortunatelly Google doesn't know Twinhead TH4100B chipset 🙁

Probably each pair of chips (close to each other) is one bank. One empty socket next to them is probably for parity (256kB x 1 bit memory).

I'm 100% sure I could get 1MB before. But it took a few reboots etc (with no battery maybe some settings get wiped?).

I don't see jumpers either. But if I only populate one bank - or what I think is a bank - the MB does not boot. Puzzled.

BTW - here are the BIOS for this motherboard.

Ok, I fired up the oscilloscope to poke the board a bit and find out what was wrong and... it worked straight away.

Since it was working, I did some tests.

Bank zero seems to be the first row of 4 modules, bank 1 the second. Bank 3 and 4 the unpopulated on next to them.

If I remove a chip from bank 1, the BIOS sees 512KB instead of 1MB as expected. If I remove a module from bank 0, the board does not boot.

What I am not sure I understand is that I have 8 chips which the board marks as "256K" and I have 1 MBYTE of RAM? The datasheet talks about 256K x 4 bit - so each module is 1Mbit? Very confusing 😀

tony359 wrote on 2021-03-23, 22:14:

Bank zero seems to be the first row of 4 modules, bank 1 the second. Bank 3 and 4 the unpopulated on next to them.

You are absolutely right, my bad. I forgot that 286 being 16bit processor needs 16bit memory 😎
So 4 chips x 4 bit is 16 bit. Third and fourth bank are those pairs of sockets for SIPP memory (which can be exchanged for SIMMs).
Information in BIOS is indeed confusing. It is not common to display "memory type" in addition to just "memory size".

BTW. What was the problem for the board not recognizing all the memory. ?

No idea. It was not recognising half of it - so one bank. Yesterday I fired it up again and it was working fine... If it happens again I'll troubleshoot more. Likely a bad chip - now I know how the banks are located on the MB it should be easier to diagnose.

Some interesting options in that BIOS for selecting memory interleave and software clock settings. That's pretty neat.

I have added everything here http://www.win3x.org/uh19/motherboard/show/7855

oh wow thank you for that Deksor!