What to do if a Mac 512k is not turning on

[pukenot]

I got a Mac 512k no too long ago, but whenever I turn it on all I hear is the speaking making tiny popping sounds. Screen does not turn on. The 4.5v battery compartment is very corroded as a battery was left in there when I got it. Anyone have any suggestions for what might be the problem or what I should do first? Thanks.

 

[GiGaBiTe]

So let this be your first hard lesson to not just expect to be able to plug in 40 year old electronics and expect it to work, you may have caused significantly more damage by doing what you did. Old gear like this *always* must be disassembled and fully vetted before attempting to power it on. And even with that, there is still a possibility of smoke, fire and explosions.

If the battery compartment is corroded badly, it has a hole in the bottom which allows leaked electrolyte to drain inside the machine, usually directly on to the analog board. And if enough has leaked, down onto the logic board in the base.

Do not attempt to power on the machine again, you will need to get a long handled T15 torx driver and open the machine to see what's going on. At minimum, the analog board is probably destroyed and needs significant repairs. If the battery has leaked all over the inside of the machine, that is hazmat and needs to be cleaned with extreme care. Lithium battery electrolyte (Thionyl Chloride) is extremely toxic, so much so that it is a controlled substance because it can be used as a nerve agent in chemical weapons. You will need a solvent and mechanical means to clean it, do not expose it to water or it will release toxic fumes and turn back into corrosive acids.

If you're in the states and have a Walmart nearby, you can buy a couple of sets of their precision screwdriver sets with extensions and double them up to get to the screws under the handle.

 

[MiaM]

If you are the kind of person who likes watching videos of people doing repairs and whatnot, I recommend checking out the videos on Youtube by Adrians Digital Basement. He has a bunch of videos working on old Macs like yours, including some repairs on the analogue board.

 

[GiGaBiTe]

Depending on how much battery goo leaked inside the machine, it may be a total loss. If he wants to spend the money, he may have to source another analog board and logic board.

 

[MiaM]

Good point. Remove the logic/digital board, inspect and take some photos. Inspect the analogue board and take some photos. Both sides for both boards. Post the photos here and someone will give a verdict of how hard it might be to repair.

 

[pukenot]

Depending on how much battery goo leaked inside the machine, it may be a total loss. If he wants to spend the money, he may have to source another analog board and logic board.

Thankfully the screws have already been removed. I took a look inside and there doesn't seem to be too much leakage. There is some rust on the metal brackets holding the board in place though. I'll post some photos soon. Thanks for the help so far!

 

[pukenot]

You can see the extensive corrosion. you can also see my jumper cable patch I made after accidently scratching some traces. I still had continuity from the scratched traces, but I repaired them just to be sure.

 

[pukenot]

Good point. Remove the logic/digital board, inspect and take some photos. Inspect the analogue board and take some photos. Both sides for both boards. Post the photos here and someone will give a verdict of how hard it might be to repair.

Logic Board looks good from what I can tell. That scratch at the bottom does not break the connections. I gave the board a wash (distilled water, 91% IPA, toothbrush) and its currently drying.

 

[pukenot]

And here is the analogue board. What do you think the corrosion could have affected?

 

[olePigeon]

Your problem is probably on the analog board. Replace the filter caps marked in yellow. Check all the caps marked in blue. Use distilled vinegar to clean up any acid & corrosion.

 

[MicroCoreLabs]

There are high voltages on the analog board so I cant recommend you do this, but if it was me I would power it up while wiggling the corner of this PCB - flexing it a little - to see if the machine beeps or boots. If it does, it could indicate if there is a bad solder joint on one of the analog board connectors. This is a very common issue which is solved by re-soldering the pins after first removing the existing solder.

 

[pukenot]

Your problem is probably on the analog board. Replace the filter caps marked in yellow. Check all the caps marked in blue. Use distilled vinegar to clean up any acid & corrosion.

Can I replace the filter caps with any capacitor of the same value or does it have to be X2?

 

[GiGaBiTe]

Can I replace the filter caps with any capacitor of the same value or does it have to be X2?

There are special capacitors on the board that can only be replaced with the same type.

The silver/clear RIFA square capacitors need to be replaced with modern X2 rated capacitors. These should be replaced, because the clear coating on them degrades and develops cracks that allow moisture to get inside the capacitor. Once this happens, it makes it more likely the capacitor will explode.

The 3.9 uF 35V capacitor near the deflection yoke connector is a special high frequency electrolytic capacitor that hasn't been manufactured in decades. You cannot use a general purpose capacitor here, or it will explode and probably take out a large chunk of the analog board. This capacitor rarely goes bad, so it's best to leave it alone. If it does go bad, you'll need to use a microwave film capacitor and figure out a way to shoe-horn it in, since those are bigger.

The bigger problem with these analog boards is failed solder joints from the heat from the smoking hot vacuum tube and poor ventilation. You'll want to reflow all of the connections on the analog board with fresh solder to rule out any bad connections. The potentiometers also get dirty, I'd recommend marking their position and hosing them down with Deoxit Gold G5 and wiping them back and forth a few times to clean them up, then set them back to their original position.

 

[olePigeon]

Can I replace the filter caps with any capacitor of the same value or does it have to be X2?

What @GiGaBiTe said. Also, the two smaller ones are Y capacitors.

I only suggest changing those old film capacitors out because they're pretty much guaranteed to blow sooner or later.

Hopefully you have a component tester or even better an ESR/LCR in-circuit tester. In any event, what I would do is remove each of the capacitors (make sure to discharge them first if you've turned it on within the last 30 minutes) and test them. They may still be good. Then I would do as @GiGaBiTe suggested and reflow the solder joints, especially where the cables plug in, the flyback transformer, and the voltage regulators. Basically anything that gets hot or experiences tension (or, preferably, just do the whole board just incase.) It's a time consuming process, but it needs to be done on these old boards.

Given how cheap capacitors are (for the ones that can be replaced), you could just replace them anyway instead of checking them. They may be fine, but also, it's relatively cheap for some preventative maintenance since you'll likely be desoldering them to test them anyway.

 

[pukenot]

What @GiGaBiTe said. Also, the two smaller ones are Y capacitors.

I only suggest changing those old film capacitors out because they're pretty much guaranteed to blow sooner or later.

Hopefully you have a component tester or even better an ESR/LCR in-circuit tester. In any event, what I would do is remove each of the capacitors (make sure to discharge them first if you've turned it on within the last 30 minutes) and test them. They may still be good. Then I would do as @GiGaBiTe suggested and reflow the solder joints, especially where the cables plug in, the flyback transformer, and the voltage regulators. Basically anything that gets hot or experiences tension (or, preferably, just do the whole board just incase.) It's a time consuming process, but it needs to be done on these old boards.

Given how cheap capacitors are (for the ones that can be replaced), you could just replace them anyway instead of checking them. They may be fine, but also, it's relatively cheap for some preventative maintenance since you'll likely be desoldering them to test them anyway.

Thanks!

 

[pukenot]

I've realized that the buzzing sound might not be coming from the speaker, but instead a component on the analog board. I'll replace the rifa caps when the new parts come in and see if that changes anything.

As I was typing this message, I had the mac plugged in (turned off) and the C38 rifa cap popped and blessed me with its magic smoke! I guess that answers my question on what was buzzing lol

 

[olePigeon]

Looks like it was sooner than later.