Holy shit, you’ve found a 286 motherboard with external cache!

Too bad there’s no simm slots.

disaster wrote on 2023-08-10, 13:09:

Hello Everyone. I'm about do fix an interesting (at lest for me ;) ) 286 motherboard. Unfortunately I can't find any details abo […]
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Hello Everyone.
I'm about do fix an interesting (at lest for me 😉 ) 286 motherboard. Unfortunately I can't find any details about it.

Chipset - ACT 27C000
CPU CS80C286-20

Marks on PCB:
35-7009-02-00
Advanced Computer Rech
9038 A/W:710009B

Is there anyone who can recognize that MB?

Picture bellow.
aIMG20230808232427.jpg

Did you check for clues on TheRetroWeb, particularly Advanced Computer Technology & LTI boards (may be some PCPartner / VTech dna going on here?)

https://theretroweb.com/motherboards/?manufac … 42&showImages=1

https://theretroweb.com/motherboards/?manufac … 17&showImages=1

noting similar style board markings / use of the ACT A27C000 chip

Anonymous Coward wrote on 2023-08-10, 14:07:

Holy shit, you’ve found a 286 motherboard with external cache!

Too bad there’s no simm slots.

pretty sure those sockets are for DIP/DIL 32 or 64kb DRAM chips, not cache.

Look at the three long Intel chips. P5164-25. That's 8x8k 25ns SRAM.

Agree the Intel p5164 are static ram, and could be a cache. 35-7009 sure does resemble the standard Vtech/PcPartner early numbering of 35-xxxx.

Hello again 😀

PC Hoarder Patrol wrote on 2023-08-10, 15:08:

Did you check for clues on TheRetroWeb, particularly Advanced Computer Technology & LTI boards (may be some PCPartner / VTech dn […]
Show full quote

Did you check for clues on TheRetroWeb, particularly Advanced Computer Technology & LTI boards (may be some PCPartner / VTech dna going on here?)

https://theretroweb.com/motherboards/?manufac … 42&showImages=1

https://theretroweb.com/motherboards/?manufac … 17&showImages=1

noting similar style board markings / use of the ACT A27C000 chip

Yes - I was searching there. I can't see any similarities. The design of the board is quite unique.

Anonymous Coward wrote on 2023-08-10, 14:07:

Holy shit, you’ve found a 286 motherboard with external cache!

Too bad there’s no simm slots.

Yeap - there is even a jumper JP1 which allows you to enable/disable the cache.

Horun wrote on 2023-08-11, 01:17:

Agree the Intel p5164 are static ram, and could be a cache. 35-7009 sure does resemble the standard Vtech/PcPartner early numbering of 35-xxxx.

I've even found something similar in Russia (same chipset and CPU manufacturer, identical way of jumpers/components description):

35-7008
So yes it must be some Vtech/PcPartner mobo.

Ok, so maybe someone could tell me what kind of RAM chips should I use here?

Same type as on the board or equal 256k x 4 20 pin DIP dynamic ram at 80nS or faster (yes board has 70's but 80's might work OK. EDIT: no you probably need 70nS or faster, missed the cpu is a 20Mhz).
You want 8 of them. Best not to buy from China....approx cost about $40.
It currently must be jumpered/switched for non-parity as there are no parity chips (the smaller 16 pin dips), if the board boots OK as-is then do not worry about the parity chips....

Horun wrote on 2023-08-12, 23:36:

Same type as on the board or equal 256k x 4 20 pin DIP dynamic ram at 80nS or faster (yes board has 70's but 80's might work OK. EDIT: no you probably need 70nS or faster, missed the cpu is a 20Mhz).
You want 8 of them. Best not to buy from China....approx cost about $40.
It currently must be jumpered/switched for non-parity as there are no parity chips (the smaller 16 pin dips), if the board boots OK as-is then do not worry about the parity chips....

So I guess HY534256S-70 will be good enough.
Out of curiosity - do you know parity ICs? For HY it should be HY53C256LS-70 I guess, but any other?
Every regular 256kx1 with 70 ns or less?