Weird crashes on my MAC 512k

[Builder68]

Hi there to everyone!

This would be my first post on any internet site! (That tells something about my age for sure!)

I am writing to you from afar as a newcomer seeking help with a recently acquired Macintosh 512K. Please excuse any grammatical errors, as English is not my native language. I find the use of Google Bard/Genie to rephrase my writing quite interesting, don't you think?

I am facing error codes 0F0002 and 0F0003, but with an unusual twist:

If I turn on the machine after it has been off for a few hours, it actually boots up! However, within a minute or so, System 6 crashes with "Illegal address/instruction" errors.

I would be deeply grateful for any guidance anyone can offer in troubleshooting this issue. I am eager to learn more about my Macintosh and bring it back to full functionality.

I have already tried the following:

• Reseating the original ROM chips
• Adjust Voltage (Originally reads 5.42V and 13.63V. Now is 5.1V and 12.47V)
• Resold joints of J1 & J4 connector
• Installing and booting from ROM-INNATOR OS (Ctrl+R)
• Booting from floppy disks
• Booting from a floppy emulator

I suspect that bad RAM is the issue, but I also noticed that when the floppy drive is working, there is a slight horizontal stretching on the screen that coincides with the sound of the motor.

Regards,

Builder 68

 

[cheesestraws]

Welcome to the forums!

0F0002 and 0F0003

System 6 crashes with "Illegal address/instruction" errors.

0F0002 and 0F0003 are error codes for Address Error and Illegal Instruction, so the symptoms are consistent.

It could be bad RAM, but the period between turning it on and the error occurring feels heat-related to me: usually things that reliably start breaking after some time are due to heat buildup. I might suggest looking at the joints around the RAM chips, although this is a bit of a wild guess. Also, I'd suggest measuring the output from the PSU as the machine warms up.

You might find it helpful here to get some cold spray / freezing spray, and hit various parts of the computer with it when it's broken to see if you can get the brokenness to stop...

 

[bibilit]

but I also noticed that when the floppy drive is working, there is a slight horizontal stretching on the screen that coincides with the sound of the motor.

i will think this is related with voltages from the PSU, (apparently already adjusted but the former values where already far gone)

As cheesetraws suggest, will check voltages at different stages.

 

[68kPlus]

If it is the screen, you'll need to recap your analog board. I'm doing that with mine sometime in the future, just for longevity's sake.

 

[Builder68]

Welcome to the forums!




0F0002 and 0F0003 are error codes for Address Error and Illegal Instruction, so the symptoms are consistent.

It could be bad RAM, but the period between turning it on and the error occurring feels heat-related to me: usually things that reliably start breaking after some time are due to heat buildup. I might suggest looking at the joints around the RAM chips, although this is a bit of a wild guess. Also, I'd suggest measuring the output from the PSU as the machine warms up.

You might find it helpful here to get some cold spray / freezing spray, and hit various parts of the computer with it when it's broken to see if you can get the brokenness to stop...

**Problem solved! **

First off, I took your advice and checked voltages everywhere. Then, like you suggested, I gave the motherboard a frosty makeover with some freeze-spray cleaner. That white stuff looked like a mini ice rink for a while! After putting everything back together, the machine still crashed... but hey, it lasted 5-6 minutes this time! Illegal address errors again, but definitely an improvement. You were right on the money about those loose connections acting up when the machine heats up. Makes sense, right?


Second, check this out: I found cracks in one of the solder joints on the J1 connector (see pics!). Even though it seemed like is the speaker output and the sound is ok, I went ahead and resoldered the whole connector just to be safe. And guess what? Boom! No more errors so far. An hour later, and the machine is running smooth as butter. Who knew tiny solder cracks could mess up the memory bus like that? Never would have guessed!

Huge thanks for your awesome advice, man! You definitely saved the day.

Attached some pics!!

 

[Builder68]

I also noticed that the subtle horizontal flickering on the screen when the floppy drive spins up is practically gone now! It seems like the culprit was a loose connection in the J1 connector on the motherboard, which caused a voltage drop.

 

[cheesestraws]

**Problem solved! **

Hooray!

Yes, those analogue board connectors are well known for developing hairline cracks: the cooling isn't as good as it might be on those machines, and the repeated thermal stress has lead to cracks in many of them. Interestingly, one of my Pluses had cracked joints on J1 too (the Plus having the same analogue board as the 512k), but that only affected video, and the crack must have been bigger because it meant I needed to wallop the side to get it to work. I've never seen that result in what looks like RAM errors before, so I'll remember it. Thankyou for the details and pictures!

 

[Builder68]

Digging deeper, the issue wasn't just a simple dip in voltage. Instead, cracked solder joints in the J1 connector on the Mac motherboard are likely causing high-pitched electrical noise. This noise bounces around and messes with the electrical resistance and balance within the motherboard, causing major disruptions to other signals. This, in turn, leads to data errors, instability, and performance problems. Importantly, the J1 connector carries signals that control the timing of the display (HSYNC and VSYNC). This means the cracked joints could very well be spreading this electrical noise directly to the data bus, causing even more problems