Sad Mac error 0F0002 on a Mac 128K

[retrobecanes]

I bought a Mac 128K a couple of weeks ago.  Both its internal and external drives are defective and are in need of repair, so I cannot use them with the computer right now.  In the video link below, the internal drive has been removed and the computer is not connected to any external drives.  You will see that after a few moments it crashes to a Sad Mac with an error code 0F0002 and produces some video artifacts.  It must also be noted that the memory test (turning computer on while pressing on the interrupt button) does not complete.  It stays on the memory check code 0F000D and never seems to stop.  While I cannot use M0130 drive as they are defective, I was able to boot the 128K from a Floppy Emu (http://www.bigmessowires.com/floppy-emu/).  Initially I was able to load System 2.0 and actually use it for a while.  I just had to load the boot image quickly.  If I went too slow the 0F0002 sad mac would show up and I had to reboot the computer.  But after a while I could not do that anymore, regardless of how quickly I would load the boot image, the 0F0002 would show up immediately and I could no longer load an image.

video link: https://youtu.be/CkYbpHbB0Ak

I am having the computer re-RAM'ed as this seems like one of the most plausible causes at this point but I have no certainty that this will fix the problem.

I was also planning to perform the following tests in the hope of identifying the root cause of the problem:

- check Mac 128K voltage at the disk port pins

- identify if the problem is on the logic board or the analog board by swapping boards between my Mac Plus and the 128K

I was wondering if anyone else had experienced this issue and if you had any other recommendations for tests or troubleshooting procedures.

Thanks!

 

[bigmessowires]

0F0002 is an address error, which isn't super helpful. It's likely just a symptom of some other problem related to RAM or ROM.

The Mac always performs a memory test when it's powered on - no need to hold the interrupt button. If you turn on the power while holding the interrupt button, the computer will always crash with code 0F0002 because no interrupt handler has yet been installed. The interrupt button doesn't work until the OS has been loaded and has installed a proper handler routine.

 

[retrobecanes]

Thanks Steve, I figured that 0F0002 was probably a diversion since there was no software being loaded when it occurred.  I will give this another try once the RAM has been replaced and will see if the problem persists.  Also, I was wondering if the problem could be due to the Mac 128K not having an internal drive installed in this case.  Any thought about that?

 

[bigmessowires]

If you turn on the power while holding the interrupt button, the computer will always crash with code 0F0002 because no interrupt handler has yet been installed. 

Sorry, I meant to say that it will always crash with code 0F000D in that case, which is just the error code for a non-maskable interrupt. So the behavior you're seeing there is perfectly normal.

Not having an internal drive shouldn't be a problem. The behavior from your video is odd. I would guess there's some component or logic board trace that's just on the hairy edge of failure. It works for a few seconds, but after enough time passes (maybe due to the system temperature warming up), it fails. What happens if you hit the reset switch after the 0F0002 sad mac?

Replacing the RAM seems like a good thing to try, in the absence of other clues.

 

[retrobecanes]

I should be getting my board back later on this week with the new RAM and also new F253 ICs,  I had read in the book 'Dead Mac Scrolls' that the error 0F0002 could be due to failing F253 ICs (AS253 chips at board locations G3, G4, F4, and F4) or blown traces in that area.  After inspection, there is apparently no blown traces there but it didn't hurt to have those ICs replaced at the same time as the re-RAMing.  Hopefully that will do it. In any case, I will come back to this thread and post an update when I know more.  Any chance that this could also be due to an issue on the analog board?

 

[bdurbrow]

In general, bad power can cause digital issues... if you know somebody with an oscilloscope; you can have them check out the power rails coming out of the analog board. The only other connections to the analog board from the logic board are all one-way from the logic board to the analog board; so I would tend to think that it is unlikely that they would cause the issue that you are seeing (although, EMI can do weird stuff sometimes...).

 

[retrobecanes]

Update: the re-RAM of the logic board seems to have fixed the problem.  The 0F0002 error has disappeared and the Mac 128 is stable!