Apologies, I'm a little late here but I had been wondering the same thing. I've been gathering part numbers for 128kx8 SRAM (attached), but am not sure if any of them are mixed-mode. UMC clearly spells it out on their data sheet, but I haven't checked the others yet. Either way, I've attached some good part numbers for you. Finding them is another thing entirely...

Edit: Turns out I've got 5 UM61M512k-15 chips in my drawer. Maybe we should organize an SRAM swap around here... Somebody's got to have what you need. 😜

Finding authentic 12 ns 128kx8 will be a challenge. Have you found any?

I've given up on finding 3.3V/5V mixed mode 128kx8 chips at 15 ns. Possibly someone will come along and offer me the 4 pieces I need.

Unfortunately no. So far I've only found them from suppliers in China & Hong Kong, but I don't trust the authenticity... There are tons of the ISSI chips knock offs, but that's a risk. I've gotten bad batches where the chips aren't actually the advertised size or speed.

I'm going to continue my search though--These things have got to be out there somewhere.

Well, the ISSI 10 ns knock-offs seem to work, minus a 10% failure for DOA chips. I've used 10 ns knock-off chips for motherboards which require 12 ns as the TAG RAM and I haven't had issues, even with the FSB at 83 MHz.

Do you know of any method to test their capacity & speed? Have you seen an instances where they report as 1Mbit, but actually operate at less?

I'm able to test chips with a TL866+ for functionality, but not for capacity or speed.

As recent as 6 or 7 years ago, there was some new old stock testing systems for these modules, but the guy wanted $850 USD. I'm not sure if that company is still in business. If you are interested in paying $850, I will dig through my emails for the company name and contact information.

So far, they have all been 1 mbit in size, it is the speed that I question. The best option for this might be to setup some kind of custom circuit and measure the response time with a scope or logic analyser.