Atari 800XL RAM Replacement

[SkullBlade]

I'm kind of stuck right now, I have an Atari 800XL here which refuses to boot to the BASIC prompt. Instead, it gets stuck on a memory test screen showing quite a lot of bad blocks on the RAM.


Anyway, the RAM in my 800XL is not socketed, so that's going to be a pain. My issue is I can't find anywhere to get replacement RAM from, does anybody know where I may be able to purchase some compatible RAM?


Or maybe I'm better off just replacing the machine, I dunno.


It appears to work fine with cartridge games though.

[Bryce]

The 800XL uses standard 4164 RAMs, you'll often find them on ebay, or you can even buy them new from several suppliers like this one: http://www.reichelt.de/Drams-Srams/4164-120/3/index.html?;ACTION=3;LA=446;ARTICLE=2460;GROUPID=2954;artnr=4164-120;SID=13UKjx9X8AAAIAAHDkt847e204fbc907583bc6b4969d1d7823f26

Bryce.

[TFM]

Maybe some other chip (cpu) has a wobbling problem. Such a big amount of errors in RAM is IMHO rather unexpected.
Try clean pins of ICs in sockets, check cable connectors and soldered parts for a break in wiring

[Bryce]

Unfortunately, dead or dying RAM is a very common problem in the Atari 800XL. It's usually only one IC that has died, but because of the way the RAM is structured, a single broken IC will report RAM errors all over the place.

Bryce.

[Gryzor]

Good job with the memory testing routine, then

[Bryce]

It's the same on most 8-bit computers. They use 64K x 1bit chips. So Bit 0 (D0) of ANY address of the entire 64K is one the first IC, bit 1 of any address is in the next IC. So if one IC fails completely, the entire 64K are reported as faulty.

The good thing about this architecture, is that measuring the data bus will often show you which bit is dodgy and let you know what chip needs to be replaced. The RAM test on the 800XL is nice, but it's really not telling you the whole story. Usually a section of a RAM IC will fail, so that Bit X will be damaged in one particular 16K range, but the other 7 bits in that range should be fine.

I often get asked the standard question about the XL/XE RAM test: "The second block is red, which IC do I need to change?". Unfortunately, the answer is: "It could be any one of the 8 RAM ICs". If the XL/XE test had just 8 boxes, one for each bit, it would be a lot more useful.

Bryce.

[SkullBlade]

Ah thanks, it's quite expensive to get those chips here so I've ordered 2 of them for now, since you said any number of chips could be dead but the number could be small, I will go from there and order more if I need them.


I would have posted a picture of the memory test screen to see if its possible to estimate how many could be dead, but from what you said it sounds like that would be useless. I'll wait until these chips arrive anyway and see where it goes from there.


Thanks

[Bryce]

You can piggyback test them. Cut the 5V pin of the first IC, as close to the pcb as possible. You'll need a decent fine cutters to do this, don't do it with an ugly big cable cutters. Then bend the pin slightly outwards. Bend the 5V of the new IC too and connect a lead to it that you can connect to 5V from somewhere else on the PCB. The push the IC onto the old one and start up the computer. If the problem is identical, bend the pin back down and solder it back in place and continue until you've found the dodgy one. Make sure the 5V pin of the new IC definitely doesn't touch the bent up 5V pin of the old one.

Bryce.