My educated guess (being unable to identify the board) would be a normal DX2 or an overdrive DX4 CPU-wise. As for a hard drive, this style of AMI BIOS often limits it to 512MB (no LBA support).

Would it have to be a DX4 Overdrive, or would a non-Overdrive DX4 work?

Is there anyway to update the bios to accept a larger hard drive?

Thanks.

It's a voltage thing. Non-overdrive DX4s use 3V-3.45V, this board can only do 5V. Interposers exist that can regulate the voltage down to 3V, but they are rare. I found one (broken, and repaired it) and use it to run a DX4-100 on a board like this.

As for HDD - possibly there's a newer system BIOS that accepts something (slightly) bigger, but don't count on it. If you have a network card with a ROM socket, take a look at XTIDE.

post a full mobo pic, the best upgrade would be some cache memory since I don't see any getting reported

keropi wrote:

post a full mobo pic, the best upgrade would be some cache memory since I don't see any getting reported

In the last pic you can see empty sockets in the background. That would definitely help.

Board looks weird. VTech chipset, CL onboard graphics. Probably would be nice if upgraded by a 487. Makes the machine even more weird. 😀

Because the socket is 168-pin rather than 169, there is a good chance that a normal CPU will work. I would definitely track down the manual first. Some of the boards with soldered CPUs will only accept CPUs with the 487 pin configuration. Those sockets will only accept ODP type overdrives. ODPR overdrives have standard CPU pinout.

Here are some additional pics. Hope they help. Thanks.

Yeah, there is definitely room for a cache upgrade. There are even jumper settings for SRAM type selection. Other than that any 5V 486DX will be an upgrade, due to the FPU. However it is questionable if you will notice a speed difference, since e.g. Quake won't run well on this machine anyway. Nice thing: it seems to have a local bus graphics card. That should be reasonably fast.

What kind of cache chips does this use? I'm never installed cache before and am not sure what to look for on eBay.

Also, as this is a 25mhz system, would I be limited to CPUs that are a multiple of 25mhz (eg 50mhz, 75mhz)? Or, do you think a DX2 66 will work?

My current plan is to upgrade to a DX2 66, max out the cache (once I know which type to buy) and install an IDE controller card with an onboard bios support up to 8.4gb hard drives (which I do have).

Also, I would not be trying to run Quake on this. I have plenty of Pentium 1, 2, and 3 systems for that. I was thinking earlier DOS games like Commander Keen, Wolfenstein, Doom, etc.

Thanks for all the help so far!

It's hard to say without the manual but I don't see any way to disable that PQFP processor, so that signal is probably routed to the upgrade socket. Which means only 487 or ODP overdrive will work. So don't buy that DX4 just yet.

EDIT: Or maybe I've misunderstood the JP6 description. It's problaby that jumper that does it. In that case ODPR or any DX/DX2/DX4 (so long it's a 5V one) will work.

Question on the cache upgrade.

It appears that this motherboard can take 32kx8 and 32kx9 SRAM chips. What is the difference between the two? Is one faster than the other?

Also, I see 4 SRAM sockets. Would I just search on eBay for 32kx8 or 32kx9 SRAM cache and just buy 4 of them? Are they all the same capacity?

I have no clue. Please help.

Thanks.

In the corner at the back away from the keyboard connector I'm expecting a "35-xxxx-xx" marking for a PcPartner/Vtech board. If you reply with that marking and/or make a full overhead layout picture we might be able to tell which model.

tegrady wrote on 2019-02-25, 15:16:

Question on the cache upgrade. […]
Show full quote

Question on the cache upgrade.

It appears that this motherboard can take 32kx8 and 32kx9 SRAM chips. What is the difference between the two? Is one faster than the other?

Also, I see 4 SRAM sockets. Would I just search on eBay for 32kx8 or 32kx9 SRAM cache and just buy 4 of them? Are they all the same capacity?

I have no clue. Please help.

Thanks.

Better late than never:
This board is a PcPartner/ VTech 35-2566-00. It is not yet documented on theretroweb.com.
With JP1 and JP6 in the appropriate position it can run 5 Volt AMD and Intel 486DX and DX2 class processors. If you want to run a lower voltage CPU you will need an interposer. If you want to run a 4x multiplier the interposer needs to support that.

With JP2 you can set the FSB:
FSB\JP2 1-2 3-4 5-6
16MHz open close close
20MHz close open close
25MHz open open close
33MHz close close open
40MHz open close open
The 12MHz and 44MHz that the clockgenerator supports are not supported by the motherboard.
The ISA bus is automatically set to FSB/4 for FSB upto 33MHz and to FSB/6 at 40MHz.

So if you want to run a Intel 486DX2 66 you need to: Close positions 1-2, 4-5 and 6-7 on JP1, move the jumper on JP6 to position 2-3 and close position 1-2 and 3-4 on JP2.

For the L2 cache you will need two 8Kx8-bit DIP28 SRAMs and four 32kx8-bit DIP28 SRAMs, 20ns or 15 ns will do. Put the two 8kx8 SRAMs in the two 28 pin DIP sockets. Put the 32Kx8 SRAMs in the 32 pin DIP sockets with pin 1 of the chip in contact 3 of the socket. You should end up with a neat rectangle of six chips. Don't forget to enable the L2 cache in the BIOS.
Although the 32 pin DIP sockets suggest otherwise the chipset does not support more than 128KB of cache.
For the 8Kx8-bit DIP28 SRAMs search for W2465AK, UM6164BK or AS7C164.
For the 32Kx8-bit DIP28 SRAMs search for W24257AK, UM61256AK or IS61C256A.

The L1 cache of the CPU can be switched off with the key combination Crtl+Alt+Numpad[-] and switched on with Ctrl+Alt Numpad[+].