Classic sad Mac 00000003 00040000 after recap and cleaning

[elemenoh]

This Classic had Sad Mac error 00000003 00040000. Caps were bad, but the board was in good shape. Replaced the caps all and ran the board through an ultrasonic cleaner. After, it still showed the same error.

I replaced and cleaned underneath UH6, but no change. Installing the RAM expansion just changes the type of distortion.

It's unclear if the Sad Mac error decoder applies to the Classic. If it does, I'm not sure how to do the math to narrow down which chip(s) are bad. 

I saw this post with the same symptom, but it was for an SE, so has a different MLB. I've started to check continuity but so far no problems.

Assuming this is likely due to a bad RAM, can someone help decipher which chip(s) are failing?

 

[SuperSVGA]

If the error is to be believed it's bit 18 of bank B.

For future reference:

Example:
$AABBCCDD

AA=8 bit mask for bits 31-24
BB=8 bit mask for bits 23-16
CC=8 bit mask for bits 15-8
DD=8 bit mask for bits 7-0

So with your code of 00040000 and with the masks expanded, it looks like this:

31                                                                     0

00000000 00000100 00000000 00000000

Maybe a scope or logic probe on the address lines might show you something?

Here is the memory page of the schematic:

 

[elemenoh]

Does that particular bit implicate a particular chip or address line?

 

[iJol]

Hey,

did you found a solution for the problem?

Got a Mac Classic with the same 00000003 error, but my Mac says it's 00008000.

 

[dochilli]

The RAM test in bank B failed. The Z field indicates a failed bit.

Could be a broken RAM.

Not sure, but can be bit 15:
00000001 Bit 0; 00000002 Bit 1; 00000004 Bit 2; 000000008 Bit 3; 00000010 Bit 4 and so on

00008000 could be bit 15
I do not know, if this is the right interpretation.
Do you have a memory expansion? Then I would try to remove it and boot with 1MB on the LB, but it could be a broken ram on the LB too.

 

[iJol]

Yep, it was indeed a broken RAM. The two chips on UK1 and UK2 were slightly warmer then the rest, so I used my Hantek Oscilloscope to check all the RAM chips on board and figured out that Pin 18 DQ3 on UK1 and UK2 showed a weird pattern compared to the other chips. Replaced them with two chips of a spare Memory Expansion Card and it booted right into the ROM-Disk.

Compared to the schematics and your guess:

Not sure, but can be bit 15:
00000001 Bit 0; 00000002 Bit 1; 00000004 Bit 2; 000000008 Bit 3; 00000010 Bit 4 and so on

00008000 could be bit 15

sounds right, cause Pin 18 on UK1 and 2 goes to Data Bit 15 according to the schematics.