Upgrading an SE FDHD to 4 MB doesn´t work

[feltel]

Hello there,
I'm new to the classic Mac world and bought me an SE FDHD recently. Unfortunately this was battery bombed and probably beyond repair. I got me a replacement motherboard which once was an original Apple repair part. The board does look ununsed. I installed 4 identical 1MB SIMM modules and removed the RAM config jumper. Upon powering on I got an sad Mac and an error code 00000005 00820082. I tried different sets of RAM modules and I got different sad Mac codes. The second line of the code probably changes on every power up. If I set the RAM config jumper to the 2/4MB position I can power up the Mac and boot it to System 6. The Finder reports 2 MB and the Mac is useable. I don´t know if the board then uses only one of the two banks or only half the capacity of each module.

I tried RAM modules from Samsung, Siemens and NEC, with or without Parity. 70ns or 80ns. It does not seem to make any difference. On every change of the modules I fear breaking the retaining clips of those slots. :-O I cleaned the contacts of both the modules and the slots and used contact cleaner.

Am I missing something? Please help a classic Mac novice to get the little machine up and running.

 

[finkmac]

Consulting the Sad Mac Error codes article:

$0005

The RAM External addressing test failed. The Z [lower line] field indicates a failed address line.

 

[feltel]

I found SE schematics at https://archive.org/download/Macintosh68kSchematics but they are barely readable. Are there any better ones somewhere? Arent all adress lines used when only half the capacity is set? Also the second line changes every time I power the machine up. This leads me to believe there is something else than a broken address line.

 

[Phipli]

I found SE schematics at https://archive.org/download/Macintosh68kSchematics but they are barely readable. Are there any better ones somewhere? Arent all adress lines used when only half the capacity is set? Also the second line changes every time I power the machine up. This leads me to believe there is something else than a broken address line.

Probably worth starting by spraying contact cleaner into the SIMM slots and cleaning the RAM SIMM contacts too.

 

[feltel]

I did this unfortunately without any effect.

 

[feltel]

I fiddled around with the RAM modules out of pure interest. Two modules in Slot 1 and 2 and I have a sad Mac. The same modules in Slot 3 and 4 and the machine starts. Then I mixed modules which I normally wont do. Two Siemens modules in Slot 1 and 2, and two Samsung ones in 3 and 4, the machine started. The RAM config jumper was at the 2/4MB setting, so I ended up with 2 MB total. Then I removed the jumper and tried my luck. The machine bootet and showed 4 MB RAM. I cannot believe it. Why does it not work with 4 identical Samsung ones or the NEC ones? Tomorrow I have to find some kind of system check tool where I can run a full memory diagnostics. I this is stable and without errors I wont touch the RAM modules any more.

 

[Realitystorm]

If you haven't seen this guide, it may help https://archive.org/details/apple-memory-guide-may-2000/page/n4/mode/1up, according to it you remove the jumper for 4MB, so when you finally removed it, that's why it worked, so the other memory combos you did were likely fine too.

 

[Realitystorm]

I have some guides on my site that may help you https://www.savagetaylor.com/downloads/downloads-macintosh/

 

[feltel]

Removing the jumper is what I did. Thanks for the link to the memory guide. The guide notes to put the memory modules in slot 3/4 for a 2mb config. I found it out trial an error. Then it states for a 2,5mb config to put the higher density modules (aka the 1mb ones) in slot 1/2. The table tells exact the opposite. Also why is the jumper labeled 2/4MB when I have to remove it for 4MB? Does it mean 2 of 4 MB?

 

[feltel]

To finish this thread I can happily report that the machine is running fine with the mixed RAM modules. I ran Snooper RAM test in a loop for a while now and it seems fine.