Macintosh 512k no boot

[TheUnknown]

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]

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.

https://vintageapple.org/macbooks/pdf/The_Dead_Mac_Scrolls_1992.pdf

 

[dalek]

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

 

[TheUnknown]

I’ll take a look when I get back from my classes

 

[joshc]

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]

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

 

[TheUnknown]

Correction that resistor gives a normal reading after testing it again