Error code 0F0002 after identifying faulty RAM chips on Macintosh 128k

[bvc]

I recently acquired a M0001 Machintosh 128k and am trying to repair it. On power, it gave a sad mac 04 RAM error code that identified faulty RAM chips. I identified them and piggyback new ICs (I have yet to replace them). Afterward, the sad mac code changed to 0F0002 which apparently means address error.

I haven't seen much explanation for what exactly the 0F0002 error refers to and it seems like some people had it go away after a complete replacement of the RAM. The Dead Mac Scrolls suggested checking the chips at G3, G4, F3, F4 for damage which I did and saw no obvious problems (I don't currently have replacements for the AS253).


The mac came with an original floppy disk which I assume is a boot disk. However, the disk seems to be jammed in the floppy drive and I have been unable to remove it either electrically or mechanically using the release pin.

Does anyone have an idea how I should proceed with fixing the 0F0002 code or have any experience with the Macintosh 128k floppy drive and how I can release the disk or at least check if it is working?

Thank you!

 

[MacTech68]

Which model of floppy drive is fitted? Pics may also help.

Has the logic board ever been upgraded? Again, a pic or two may assist.

For the 0F0002 problem, I'd at least check the +5 volt rail and adjust as necessary.

 

[bvc]

Which model of floppy drive is fitted? Pics may also help.

Has the logic board ever been upgraded? Again, a pic or two may assist.

For the 0F0002 problem, I'd at least check the +5 volt rail and adjust as necessary.

Certainly, the floppy drive is a SONY OA-D34V. I have attached some photos.

I don't believe the logic board has ever been upgraded as it has (what I believe is) the original 4264 RAM chips (I attached a photo).

The +5V rail (read as pin 5 on the external floppy connection port) is reading +5V as it should.

Thank you for your help!

 

[MacTech68]

Excellent photos - As an aside, this board would probably been finalized around 1984 Week 36. However, sometime after 1986 Week 40, it would have been a Apple Service replacement part (going by the replaced RAM IC at F10).

I'll agree that this appears to be a non-upgraded 128K. Final check would be the two pins circled below should be joined on the solder side of the board with an original track - check continuity with a multimeter.

As for the Floppy drive, if it's never been cleaned and re-lubricated, you'll need to disassemble and clean it.

Here is a great guide:

The Sony Model OA PDF.pdf

drive.google.com

And you could read this in conjunction with the above guide:

3.6.1. The floppy drive refuses to eject, or I can't insert a floppy in it. How do I repair it?

The only warnings I would give is to not lift the disk/head clamp too high as you can stretch the spring. Also, resist the temptation to wrench a jamned diskette - I've seen many a head broken. Finally, ensure the pressure pad is present on the end of the disk/head clamp upon re-assembly, arrowed here:

Finally, can you read the +5 volt rail to 2 decimal points ? eg 4.95 ?

 

[bvc]

Hi, thank you for the detailed explanation and history.

I measured the +5V rail at 5.07V and the +12V rails at 12.19V. Is the +12V rail within proper margins?

I checked the connection on row E that you mentioned. There is a printed track on the solder side and my multimeter is indicating a good connection.

I am still working on the floppy drive (perhaps being overly cautious with trying to tease it apart). I will update when I manage to get it opened up and cleaned.

Would an error with the drive cause the 0F0002 sad mac error or is it definitely a problem with the logic board? Any ideas about what could be the culprit? Do you think it makes sense for me to do a full re-RAM of the board. I am hesitant to do so because my desoldering skills are a bit rusty and I don't want to damage the board.

 

[MacTech68]

Voltages all seem good.

If you disconnect the floppy drive, do you still get the error code?

I can't be certain about the RAM being the problem. If you've not removed thru-hole discrete ICs from a 4 layer board, I'd be proceding with extreme caution. With fewer tools, it's often easier to snip the IC pins nearest to the body of the IC and remove each pin individually. you could even solder the replacement 4164 RAM IC to the pins - ugly, but should work with due care.

 

[bvc]

Yes, the error code is the same no matter if the floppy drive is connected to the logic board or not.

 

[MacTech68]

I'm a little confused. What was the original error code, and is the current error with or without piggy-backed RAM ?