Macintosh Classic Sad Mac RAM expansion error

[wintr]

Morning all,

 

I've tried a few searches on this site and on Google directly, but I can't seem to find a reference for Sad Mac error codes for the Macintosh Classic. For the SE and Plus yes, but not the classic directly. Or, perhaps I have misinterpreted what I was reading and maybe just need to have someone nudge me in the right direction? I have one Classic that will boot fine without the RAM expansion installed. With the RAM expansion installed I get a Sad Mac with the following code:

 

00000005

00100000

 

Following this document here: https://udcf.gla.ac.uk/~gwm1h/Error_Codes/Sad_Mac_Codes.html

It says: "$05    - RAM external addressing test failed. Minor error code indicates a failed address line." which follows that this only happens when the RAM expansion is in. The lower numbers should be the address line that I should be checking.  But how do I translate 00100000 into a trace on the motherboard that I should be checking for continuity? 

 

Any advice would be welcome. Thanks in advance.

[plb007]

Hi, 

 

I've got a similar problem, but without the second line (00000000)

Did you fix your problem, and (if yes) how ?

My recapped classic boots fine without the ram expansion in, but boot with this memory error when inside. 

 

Regards, 

[SkyBry]

I have the same error at boot; no sound for me, but sad Mac error shows immediately with 00000005  and address of 00080000.  If I pull the memory board out, I can get past this error and boot from the built-in system rom, but System 7 on the hard drive doesn't have enough memory to boot.  I've examined the motherboard for any damage and so far cannot find anything... it looks pristine.   I cleaned it anyway in case of capacitor leakage, but no difference in behavior.  So far I can't find a clue to the cause, but I'll post a follow-up here if I figure it out.

Edited December 1, 2020 by SkyBry
Spelling error.

[superjer2000]

I would start buzzing out all the memory lines per the schematic. If there is good continuity, there are a few chips related to memory that are generic and are cheap enough it’s worthwhile to just replace them. Of course that’s assuming the memory cards are good.  I fixed my Classic that was only showing 512k ram that way (search here for Classic 512k ram or something similar)

[dochilli]

Just an idea:

00000001 A0? ; 00000002 A1?; 00000004 A2? 00000008 A3?

00000010 A4? ; and so on?

 

00100000 would be A20?

00080000 would be A19?

Do not know, if I am right, but could be possible.

 

Edited December 1, 2020 by dochilli

[Stephen]

On 11/30/2020 at 9:45 PM, superjer2000 said:

I would start buzzing out all the memory lines per the schematic. If there is good continuity, there are a few chips related to memory that are generic and are cheap enough it’s worthwhile to just replace them. Of course that’s assuming the memory cards are good.  I fixed my Classic that was only showing 512k ram that way (search here for Classic 512k ram or something similar)

Just emphasizing this — I don't have a lot of experience with replacing ram chips, but if I learned anything from watching Adrian's Digital Basement, it's that ram chips fail very often (even new chips!)