Mac LC II Memory Issue

[macintoshmartin]

So I've recently installed 2 4MB SIMMs in my LC (which has System 7.5.3), and when I go to power on the computer, it gets stuck at the welcome to macintosh screen. I've tried to disable extensions but that didn't work, but when I tried to boot off of a 6.0.8 Disk Tools floppy it booted all the way and I was able to see I had 10 MB installed. So then I made 7.0.1 Disk Tools floppy thinking it was my hard disk installation having a problem but that also gets stuck on the welcome to macintosh screen, and when I remove the new RAM it boots fine. Anyone have any idea why this is happening?

 

[havokalien]

Two possibles

Bad/too slow of ram or failing caps on the motherboard. I would lean towards th caps. I know you saw the ram off a boot disk but when it try's to read the hard drive my SE 30 is doing the same thing.

 

[macintoshmartin]

The thing is that I've copied the system folder from the boot disk to the hard drive and it worked so I've pretty much ruled out hardware problems.

 

[MacTech68]

How many chips are there on each 4MB module?

If there's 8 (or 9) you should be fine.

If there's 4 and a single square chip, YMMV. These are bank switching SIMMS and some don't play well with Macs.

A nice clear pic of the modules, showing the numbers on the chips might help.

 

[macintoshmartin]

Right now I can't take any pictures of the ram but I can tell you that they're 30 pin parity SIMMs, one that's 80 ns and the other is 70 ns, and they both have 9 separate chips on them.

EDIT:
Added a picture of the RAM, It's a bit bad quality but I think you can see them pretty ok. The chips read M5M44100J 121SG7C-8, and they have the Mitsubishi logo on them.

 

[MacTech68]

Well, they appear to be 5V FPM which is a good start. Speed is more than adequate.

However, without other similar sized memory to test, I may have to agree with havokalien's comment about leaking SMD caps. The problem may even be etched tracks (though it shouldn't pass POST).

It's possible that the ones circled below are the culprits.

 

[macintoshmartin]

Ok, so I've looked into the capacitors and I think all of them are fine. I can't test them with a voltmeter now but none of them are leaking and I don't see any corrosion on the logic board. But I have to ask, what changed between System 6 and System 7, because the earlier one works while the newer one gets stuck on the start-up screen?

 

[gkarris]

If I remember correctly, some System 7 versions require an Enabler to work with newer (at the time) or certain Macs...

If not in this case, then make sure the Memory SIMMS are rated with the proper speed for that Mac.

 

[MacTech68]

It's possible that the System 6 Disk Tools disc is (by design) missing certain system resources such that the area of memory affected isn't accessed.

It could be faulty RAM.

BTW, I'm assuming the 7.0.1 Disk Tools is a copy of an Apple disk?

System enablers didn't become an issue until the LCIII and And System 7.1