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Macintosh 512k no boot

TheUnknown

New member
As the title suggests I have a Macintosh 512k that has been having a power issue for a few months that I’ve been trying to figure out. Whenever I turn the Mac on there is a constant ticking noise coming from the internal speaker which occasionally slightly changes pitch and turns into a sound similar to a heartbeat for a couple of seconds before going back to ticking. Along with that the flyback transformer has a risking noise coming from it. The floppy drive does try to spin up for a split second every once in a while.

All of this should be able to be heard in the video I attached.

There also seems to be inconsistent voltage throughout the entire analog board after the initial AC circuit from the wall plug

I don’t even know what could be the issue so any help would be greatly appreciated.
View attachment IMG_1889.MOV
 

pezter22

Well-known member
If you have not already recapped the analog board/power supply that would definitely be your issue. I would also check the solder joints and reflow all the pins that have a connector cable that plug into.

Since you have it open might as well clean and re-lubricate the 400k floppy drive.

Best to download a copy of the Dead Mac Scrolls which has a great troubleshooting guide for the old Macs. There's a couple of pages dealing with sounds coming from the early Macs.

 

Attachments

  • Screen Shot 2024-04-30 at 8.53.05 PM.png
    Screen Shot 2024-04-30 at 8.53.05 PM.png
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dalek

Member
I had a similar issue - the analog board wouldn't start up (which is the ticking sound) because a resistor at the bottom right was open circuit. As above check out that book and start inspecting the analog board for obvious issues... burned resistors, leaky caps etc
 

joshc

Well-known member
leaky caps etc
Caps are rarely visibly leaky on a 512k; they are more likely to be dried out on a worn out/heavily used analog board.

Heat/changes in temperature affecting the solder joints is one of the biggest causes of problems on these analog boads, but also specific component failure as well as worn out capacitors.
 

TheUnknown

New member
I can’t tell if resistor R52 is bad or not with a continuity test and since I don’t know the resistance, I can’t tell with that either but it comes up as OL
 
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