I suspect you can only upgrade to 1MB total. The current chip you have is 256K x 16 (512KB). The zip chip pictured is 128K x 8 (128KB = 1M bits) so you don't want that one.

I would try a 256K x 16 ZIP-40 chip such as MT4C16256Z or UPD424170V.

Plasma wrote on 2022-01-17, 18:57:

I suspect you can only upgrade to 1MB total. The current chip you have is 256K x 16 (512KB). The zip chip pictured is 128K x 8 (128KB = 1M bits) so you don't want that one.

I would try a 256K x 16 ZIP-40 chip such as MT4C16256Z or UPD424170V.

Excellent, I will give that a try. Thank you.

Looking at the board, it appears to have a 512K chip with a space next to it which is unpopulated - I guess you could potentially solder another 512K chip there for 1MB onboard, and then add a 1MB module. The CL GD 5428 can take up t0 2MB total so theoretically this would be doable.

Following up on this - I gave it a shot with a 512Kb chip, and wow did it not work. I got some garbled text and then an odd screen pattern upon boot and then ... the strong scent of ozone as the chip started overheating! Luckily no harm done except for a small blister from trying to pull the chip by hand, not knowing is was ultra-hot. So I guess this port is undocumented with reason, as it is not useable. Oh, well, was worth a shot.

Maybe it was installed backwards?

Yikes!!!

That is no good..

Yes, was it installed backwards?

My approach would be to buy a pci card with that chipset and the desired amount of ram and just steal the ram from it.

I assume that the pci card won’t have that ram slot though. Just surface mount chips. Which should be easy to remove and solder on.

Another thing to bear in mind: 2MB is nearly completely pointless on CL GD-542x chips. Up to 1MB you get the expected benefits (1024x768@8b, 800x600@16b, 640x480@24b), above that 2MB just gives access to a few nasty interlaced modes, nothing actually usable.

So a second 512kB is only realistic option.

As for your blister - exactly which chip were you using? Wrong way round and/or short-circuits due to soldering are likely if it's the correct chip, if not a different pinout can give this sort of effect...

Answering the questions above:
- The spec on the chip was "UPD424260V-70 V20 256KX16 FAST PAGE DRAM 40 PIN ZIP NEC", with the eBay listing here: https://www.ebay.com/itm/153203289210.
- I was completely unaware that a zip-40 form factor chip could be installed backwards. It fit each time that I seated it in the slot, and maybe I just happened to insert it the right way the first few times and another the final time. I got different results over a few tries: nothing at all at first (caused by a bent pin), then garbled text/video but a regular boot cycle (after I straightened the pin), then the final meltdown.
- I did ultimately settle on a 512K upgrade, for a total of 1M, for the reason that you've described @dionb. No real return after 1M.