View Full Version : New SIMM's clashing with old???

02-02-2001, 04:19 PM
Hi there--
Not sure what I'm missing. I'm running an 8100/80 Power Mac. I took out the 2 8M SIMM's that came with the machine [they were 70ns and I didn't want to take any chances on incompatibility]and replaced them with 2-32M/72pin/60ns SIMMs from Macgurus. The new ones matched the 2 SIMMs that I left in the machine- also 32M SIMM's/60ns. That was going to give me 72M including the 8M on the motherboard.
Problem is that I'm getting a bus error every time I try to launch with the new SIMMs involved at all. My old SIMMs work fine in the first 2 banks [closest to the center of the board], but when I replace them with the new SIMM's there, I get a bus error. When I take the new SIMM's back out and replace them with the old SIMMs, the machine boots up just fine.
Ideas on what I'm doing wrong???

02-03-2001, 12:21 PM

Sorry, working on a project for my wife. If I read your post correctly, you should have 136MB (new 2x32=64MB, old 2x32=64MB, + mobo 8MB). Did I misread your post? Are you getting a startup chime? I have never needed to do a Cuda Reset when adding/changing ram, but do it for the balance of these tests, just in case.

Things to try:
1. Blow out the ram slots to eliminate possible dust bunnies. With a flashlight and magnifying glass, look those slots over very carefully for bent/broken/missing connectors.
2. Leave the 2x 8MB simms in their original slots and add the new 2x 32MB and old 2x 32MB to other paired slots. Make sure the new are installed in pairs and the old are installed in pairs (don't intermix them).
3. Try just the new and old 32MB simms but leave those slots where the 8MB simms were empty.
4. Try just the new 2x 32MB simms but not in paired slots you have already tried. We want to confirm, in this case, that the new ram is OK. In other words, are there any paired slots that the new ram will work in?

You may think of other possible configurations and you can try the above in any order that is most convenient. Keep notes of slots and ram that works or does not work. What we are looking for is a bad ram slot or a bad simm. But remember that you can only try these in pairs of the same size. I'm at a loss otherwise. I don't have an 8100 but I did look over the pdf docs for it and could not find any necessity for using paired slots in any particular order. So paired simms in any paired slots should be OK.

Let us know about my questions above. k

02-04-2001, 03:36 AM
actually, you DO need to use matched pairs of SIMMs in each bank. In other words, one SIMM will go in A1, the other matching SIMM in B1. This is critical.

here's why: SIMMs are 32-bit devices. The bus on a NuBus Power Mac is 64-bits wide. The only way to get two 32-bit SIMMs to work in such a machine (and they were very advanced for their time) is to use them in matching pairs, in corresponding slots, creating a virtual 64-bit device.

my feeling is, if you installed the new SIMMs in the original slots, pulling your original memory, and can reinstall the original memory into those same two slots, then one or both of the new SIMMs must be defective.

please send deb an email at deb@macgurus.com and ask her to swap them out for you.

we deeply regret the hassle.


02-07-2001, 03:35 PM
Hello everyone,
Thanks very much for your replies. Sorry it's taken me a few days to catch up here. I'm at an arts colony in Vermont at the moment, believe it or not, but I've got all my computer gear up here so I'll try looking for dust bunnies, etc. before I send the RAM back. Here's hoping it's not bad RAM.
Thanks again. MJ

02-07-2001, 09:34 PM
that sounds very....bucolic?

(got you, Michael)

I'm envious.


02-07-2001, 10:07 PM
What sounds bucolic, being at a art colony or hustling dust bunnies? I can just picture Magician at an art colony!

02-07-2001, 10:32 PM
It's like living inside of a Christmas card up here--unbelievably beautiful. But I'm guessing you didn't need to know that.....

02-07-2001, 11:54 PM
if I were at an art colony, bucolic or not, I would be like those two guys in the Bud Light commercial who snuck into the painting class with that heart-stopping nude model. Beers and sandwiches, making eyes at the babes.


02-11-2001, 09:15 PM
Found it. There is one SIMM that's bad. I discovered which one by pairing them both--one at a time--with one of my SIMMs that I knew worked. One 32M worked fine with my 32M SIMM and the other one caused the computer to freeze at startup. I'll check in with Deb and try and swap it out while I'm still up here in Vermont.
Thanks for the help, all!!! MJ
P.S. It's 4 degrees up here right now. Yikes!

02-11-2001, 10:06 PM
Good for you!