megatog615 wrote on 2023-07-06, 15:07:

Other times the POST screen will complain that the cache memory is bad and that I shouldn't enable cache.

This is the definite proof that the cache messages are not fake. If this message appears, the board actually tried to enable the cache, but detected that it malfunctions grossly (like one of the four chips missing).

megatog615 wrote on 2023-07-06, 15:07:

I installed a set of rare 32-pin sram chips and one of them let out magic smoke and could cook an egg with how hot it got!

The most lilkely cause is that you inserted the chip backwards. I know it's embarassing and at first you don't want to believe it, but it happened to me, too. I have a fried Winbond 64kx8 cache chip now, wondering what to do with the other seven chips of that type...

megatog615 wrote on 2023-07-06, 15:07:

The board seems hard-wired for a 256K jumper setting possibly, given how other PCPartner boards of the same era were laid out.

The photos on the retro web show jumpers JP21-JP24 which are exactly at the position on the board where I expect cache size jumpers to be.

megatog615 wrote on 2023-07-06, 15:07:

I genuinely cannot math out the correct chips to order because of how confusing the actual amount of memory they are advertised to handle(256K = 32Kx8??? Okay, so do I need 512K chips rated at 64Kx8 to fill 4 sockets for 256K? What about TAG? Are both the sockets TAG? Or is it a TAG and a dirty socket? What math do I have to do to figure out what to put in those?)

Most likely both sockets are for tag. A 256K configuration on that board would use 4 chips of 64K x 8 for the data memory, and one or two chips at 32K x 8 for tag. Maybe you can leave a socket unpopulated resulting in a smaller cacheable area.

megatog615 wrote on 2023-07-06, 15:07:

I think I'm at my wits end with this thing. It really sucks how a 486DX @50MHz seems to be really hampered by a lack of L2 cache.

It's a DX2 @50MHz, so the FSB is at 25MHz. For that board, it's a good thing. As you only have 4 data chips, this is a single-bank cache configurations. Many 486 boards interleave two banks in the common 8-socket configuration. At 50MHz FSB, using single-banked cache would be no fun. At 25MHz, it should work perfectly given a suitable chipset.

mkarcher wrote on 2023-07-06, 19:53:

megatog615 wrote on 2023-07-06, 15:07:

I installed a set of rare 32-pin sram chips and one of them let out magic smoke and could cook an egg with how hot it got!

The most lilkely cause is that you inserted the chip backwards. I know it's embarassing and at first you don't want to believe it, but it happened to me, too. I have a fried Winbond 64kx8 cache chip now, wondering what to do with the other seven chips of that type...

Well, I remember checking to make sure but it's possible I made a mistake. In any case I don't trust the chips in that set anymore.

mkarcher wrote on 2023-07-06, 19:53:

megatog615 wrote on 2023-07-06, 15:07:

The board seems hard-wired for a 256K jumper setting possibly, given how other PCPartner boards of the same era were laid out.

The photos on the retro web show jumpers JP21-JP24 which are exactly at the position on the board where I expect cache size jumpers to be.

I'm willing to believe you on this. However, I have no idea how they are supposed to be configured. Any time I have one of the TAG sockets populated(it's a specific one, I'm not sure) with the cache sockets also populated the BIOS just says 256K enabled. When I shift the jumpers over by one, for example, it says the cache is bad.

It'd be nice if there was a similar motherboard that I might be able to copy over some configuration on. I get the feeling I might have to turn some sideways and such. However if I just try to install 256K as it seems to expect, it should just work, right?

mkarcher wrote on 2023-07-06, 19:53:

megatog615 wrote on 2023-07-06, 15:07:

I genuinely cannot math out the correct chips to order because of how confusing the actual amount of memory they are advertised to handle(256K = 32Kx8??? Okay, so do I need 512K chips rated at 64Kx8 to fill 4 sockets for 256K? What about TAG? Are both the sockets TAG? Or is it a TAG and a dirty socket? What math do I have to do to figure out what to put in those?)

Most likely both sockets are for tag. A 256K configuration on that board would use 4 chips of 64K x 8 for the data memory, and one or two chips at 32K x 8 for tag. Maybe you can leave a socket unpopulated resulting in a smaller cacheable area.

Okay. It turns out at one point I had enough chips to try this configuration but I never did. I burned one of the 32-pin chips so I'll have to wait for a new set to come from eBay. As it stands I have two ISSI IS61C256AH-15's I can populate the TAG with. I've bought way more cache SRAMs than I care to admit for this thing. Guess I'll sell all the rest if the new ones work.

mkarcher wrote on 2023-07-06, 19:53:

megatog615 wrote on 2023-07-06, 15:07:

I think I'm at my wits end with this thing. It really sucks how a 486DX @50MHz seems to be really hampered by a lack of L2 cache.

It's a DX2 @50MHz, so the FSB is at 25MHz. For that board, it's a good thing. As you only have 4 data chips, this is a single-bank cache configurations. Many 486 boards interleave two banks in the common 8-socket configuration. At 50MHz FSB, using single-banked cache would be no fun. At 25MHz, it should work perfectly given a suitable chipset.

Windows 95 absolutely crawls. Rendering windows, for example, is a tedious process and I rarely drag windows around because of it. I can't believe this performance was acceptable back in 1995(it is my family's first desktop computer) but then again, technology was moving so fast back then. The machine was made for Windows 3.1 but 95 is what it ran for most of its working life(now it is retired and plays DOS games).

I'll update this thread if the new chips work.

Okay, the chips came in the mail today. I tried them out and luckily none of them exploded. However, I am still getting CACHE MEMORY BAD errors, curiously only for a few boot attempts. I think there's some kind of "warming up" that this machine has to do for things to start working 'correctly'. For example, another issue this machine has is that you need to press the RESET button after starting it for it to POST, but after it's been on for about an hour it will start right up from cold just fine. I don't really get why this is, but I replaced the electrolytics on this board(all twenty-something as well as the ten or so on the ISA riser card) so it shouldn't be that? EDIT: I should note that I am running this machine with a modern ATX(FlexATX, really) PSU with an ATX->AT adapter cable. I don't think it's the PSU(the machine was VERY temperamental while using its original PSU).

In any case, once the machine gets its head screwed on correctly it will boot without error but will crash/hang on disk I/O almost immediately. The XTIDE in this machine will report a read error on some disks(I'm using CF cards) or hang up on first read.

I am so close to getting this working I can taste it. It may come down to me having to replace the ceramics if I have to. The machine works fine still if I disable the external cache in the BIOS so at least I haven't broken anything.

megatog615 wrote on 2023-08-08, 14:26:

I think there's some kind of "warming up" that this machine has to do for things to start working 'correctly'. For example, another issue this machine has is that you need to press the RESET button after starting it for it to POST, but after it's been on for about an hour it will start right up from cold just fine.

This sounds like some broken trace, via or solder joint on the board. Thermal expansion can cause a torn trace or broken joint to still make contact when the system warmed up.

Electrolytics could cause "warm-up" issues, too, but you already replaced them, and electrolytics failing when cold is mostly an issue with switch-mode power regulators, and most 486 boards don't have them.