According to a manual for a different motherboard with UNIchip U4800-VLX chip:
"Memory size from 1MB to 128MB, possible using combinations of 256Kx9, 1Mx9 and 4Mx9, 16Mx9 SIMM modules in two memory bank."
yes some boards are very picky about 9 chip versus 3 chip simms...

So do you think 9-chip modules would work?
What is the difference between 3-chip and 9-chip modules besides the x4 and x1 organization? Is the difference, and maybe the reason why they are not working (or at least not with the full capacity), the required refresh counter?
Both my 4 MB module types have chips with 2k refresh cycles (GM71C17400AJ6 & MB8117400a-60), hence they should need 11 RAS bits for a complete refresh.
But IF the board would just use 10 RAS bits it would only refresh the first 1 MB, right? But then, how could it ever be able to use 16 MB modules?
All manuals of motherboards with this chipset I have seen at least mention 4 MB modules. Most of them even 16 MB.
There must be a reason, may the board be picky or not...

my Unichip board works with a 3-chip 4M sim.
i have 2 different 4Mx4 kits and it works with any and two at the same time.
I can check the sim type and take a photo of them.
Regards!

ChrisK wrote on 2022-05-03, 18:48:

Both my 4 MB module types have chips with 2k refresh cycles (GM71C17400AJ6 & MB8117400a-60), hence they should need 11 RAS bits for a complete refresh.

Huh ? Both your 4mb ?? Your board needs 4 SIMMS per bank and they should always be matching SIMMS.
If you are trying to mix 1Mb and 4Mb SIMM in same bank or even mix 3 chip and 9 chip in same bank that could be most of your problem....;p

Horun wrote on 2022-05-05, 00:25:

ChrisK wrote on 2022-05-03, 18:48:

Both my 4 MB module types have chips with 2k refresh cycles (GM71C17400AJ6 & MB8117400a-60), hence they should need 11 RAS bits for a complete refresh.

Huh ? Both your 4mb ?? Your board needs 4 SIMMS per bank and they should always be matching SIMMS.
If you are trying to mix 1Mb and 4Mb SIMM in same bank or even mix 3 chip and 9 chip in same bank that could be most of your problem....;p

Well I wrote "Both my 4 MB module types" meaning I have two different models of these 4 MB modules (i.e. they have chips from different manufacturers mounted), but 4 of each type.
Of course I have mounted four identical RAM modules per bank.
The problem I described initially is that they are recognized as 4x 1MB instead of 4x 4MB leaving me unclear about the reason for this, as this happens with two different types of these 4MB modules. Sorry if I have been unclear with this.

PiotrUU wrote on 2022-05-04, 20:06:

my Unichip board works with a 3-chip 4M sim. i have 2 different 4Mx4 kits and it works with any and two at the same time. I can […]
Show full quote

my Unichip board works with a 3-chip 4M sim.
i have 2 different 4Mx4 kits and it works with any and two at the same time.
I can check the sim type and take a photo of them.
Regards!

Type / photos would be nice. Thanks!

i found a 4m 9-chip sim!
The 9-chip works with the 3-chip.
Photo:

128k cache only works up to 16M RAM !

Great, thank you!
So the chips on your 4MB modules are 2k refresh types just like mine. So that shouldn't be the problem...
Strange. Will check the board for any damage in the memory slot area.

Could you report your BIOS revision please? It's unfortunately unreadable because of the flashlight in your first pic.
I don't suspect this will make any difference, but maybe good to know.

version and bios file
checksum in the vp 390 programmer -> "006C356D"

PiotrUU wrote on 2022-05-05, 16:57:

128k cache only works up to 16M RAM !

is there any options in bios choosing cache mode write-through and write-back?
128k cache should cache for 16mb in wb mode, and 32mb in wt mode.

Can be selected.