Thread: How to check if a CMOS RAM is OK?

Originally Posted by Wonka

I have a microprocessor system (68000) that I think has suspect RAM, the thing loads up the OS from floppy disk (into RAM I assume) then throws an error that stops the show. It can stop as the OS gets loaded in, sometimes everything loads and runs correctly for half a sec before stopping on the error. My am thinking the RAM is faulty. PSU seems OK.
Syetem has run fine for years but progressivly started to throw the error, usually a reboot would sort it, but eventually it now stops every time.

My question is, can I check the RAM in my EPROM programmer by selecting a similar EPROM device?
The device under test is a NEC D43256AC = 32k x 8 static cmos ram so provided I find an identical EPROM with 5V programming voltage?? Or how else could I check the ram chips are OK?

It is easy to buy replacements but usual soldering mess looms.

hi,
That NEC D43256AC device is a static RAM, its a volatile ram, which means it not programmable.

Any CMOS 32k * 8 with same pinout should be OK

Originally Posted by Wonka

yeh thanks for that, I am aware static RAM is not programmable but I am wanting a way to test the chip not permanently store data in it. My thought was to write to it and then read/verify on repeated cycles whilst powered up.

hi,
OK,
If you can write a diagnostic program for the MCU, you could do a read/write test.
Write/read FFh and 00h to each location thru 32K

I guess the ram's not in a socket???

Whats your location.?

Unsolder the RAM chip and fit a socket in it's place, then try plugging another RAM in and see if that helps.

Originally Posted by Wonka

No the RAM is well and truely soldered in, also I have no control over the OS, all I do is stick the disk in and power up, all diagnostic is done by the code writer (circa 1991). I'm trying to find the diagnostic info but it is not easy come by.

I have already replaced the MCU (68000) and exchanged a number of chips, those in sockets. As you can see, all I can do is keep swapping parts until it works unless there is a better way!? I did have a spare fully working system to swap parts with, damn and double drat that is now dead too

Glos, UK

hi,
As you are in the UK, if you need a spare 32k*8 RAM I could send you one, gratis or test your RAM.

If needed just PM your address.

I can