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Powerbook 520/540c Power Adapter repair/re-cap

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Ran into an issue where my power adapter for my Powerbook 540c was outputting 16v on one pin, but only 2.xv on the other pin so my 540c would no longer start up. Took the PA apart(it's epoxied together) and discovered 6 capacitors. 2x 330uf - 25v, 2x 100uf 200v, and 2x 100uf 25v. The part numbers can bee seen in the picture. While the capacitors didn't look bad, I knew they were 20 some years old and it was time to swap em out. Sure enough, as soon as I soldered in the new caps I got 16v back on both pins and my Powerbook 540c is happy again!






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I thought there was a electrolyte cap on the vertical PCB near the power connector as well. I see you didn't replace the film caps.

There are some difference of opinions whether to replace them or not. 
Anyway, when I recap something, I replace all capacitors including film and ceramic one's so I know everything is new again. I have seen several film capacitors with cracks in the housing on the analog board of the 128K/512K/plus/Classic Compact Macs. 

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I would leave ceramic and plastic film capacitors alone for now. Except if these are actually paper caps you are referring to.


You probably saw cracks in clear case capacitors near the AC input on 128k/512k analog boards. These are plain old paper (or paper in oil) capacitors (usually from company WIMA). They are placed across the line and from line and from neutral to ground. When new, these capacitors were one of the best for these type of applications, as the paper has excellent dielectric properties and has very low dissipation factor. However, after 20-30 years the paper will slowly begin to degrade and turn acidic thus the capacitor will start to turn into resistor (become "leaky"). The cracks in the case will only accelerate this. So these capacitors are now known to short and fail and sometimes explode.


I replace them on sight with proper film X2 type or ceramic Y2 type ones. Commonly are present on older analog boards, but I remember seeing them also in Duo AC adapters. The proper test method is to use high voltage insulation tester, but if tested with a common capacitor tester they will almost always read high (0.1uF will read 0.14 uF, etc.), heating them with a hairdrier will cause them to read even higher, whilst a good film capacitor will stay at the same value across the all temperatures. Some universal component testers will also show voltage loss when there should not be any.


Metallic film and polypropylene film capacitors will not fail as such even after many decades. I have some from late 1950s and they still test excellent with no leakage even at few thousand volts, whilst paper capacitors from same era are all junk.

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