Sorry for the off-topic subject but my normal Macintosh forum has been down since yesterday.

Anyway, I just recently purchased a Macintosh 512K. It is very yellowed and there's a small crack on the case but otherwise, it's in great shape.

I take it apart to see if there is any capacitor leakage. First thing I notice is that there are no SMD components. AND, I only see THREE electrolytic capacitors (axial). I'm looking around and I cannot believe there are no bypass caps. Then I see them...

They look like resistors! But, the silk screen says "C1", "C2", etc. where I would normally expect caps to be. So, how common were those type of capacitors? I assume they are ceramic caps because they have the same shape and size of resistors.


Now, the three electrolytic caps appear to be 33uF (16V I think...will looks closer later). 33uF seems a little unusual. Many caps I see that size in other equipment (Apple, Commodore, etc.) are usually 47uF.
I must admit I don't know the laws of the land when it comes to choosing a capacitance size...which is something I want to learn more. But generally speaking, if a design calls for 33uF as a bypass cap, then what's the harm in using 47uF instead? As long as I keep the voltage the same or higher...is there a problem with using a little more capacitance?

In my simple mind, I see those caps as small "emergency" power supplies that help smooth things out. What's the harm in having a little more?

Granted, I'm sure there is a cutoff somewhere. Otherwise, you could put a 10K uF in there or something silly like that.

Thanks for any pointers!

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Cat; the other white meat.

47uF as a replacement for 33uF should be fine in the use case of power smoothing (ripple suppression). Apple probably saved 1/2 a cent on the board by using parts with little headroom above the design spec.

I've seen little yellow axial bypass caps in some 80's 90's era equipment. They look similar to these modern devices.
https://www.digikey.com/en/product-high ... capacitors

There are/were color coded capacitors, but they're most often found in devices predating the home computer era all together.

Thanks for the info.

Attached is a screenshot of some of the caps.

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Cat; the other white meat.

Yes, those glass bead caps were popular in the early to mid 80's. IIRC my original Vic-20 used those on the PCB as well. I suspect they're still fine. Just replace the electrolytics and check for poor solder joints and you should be good to go for another couple decades.

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Regards, KM
https://github.com/floobydust

The Apple IIe and IIc use the same type. No wonder, they are produced at the same time.


On my Mac 512 motherboard the capacitor nearto the ROMs and the IWM is there to "smooth" the -5V generated by the 7905. You can change this one to 47uF. C22 beside the power connector is part of the reset circuit: 4.7uF/35V. I would not change this value too much. C5 nearto the mouse and disk port "smooths" the +5V: 33uF/16V. You can change this capacitor to nearly whatever you want

Regards, Ralf