Macintosh 128k Analog Board Recapping

[rushfan82]

I am beginning the process of recapping the analog board on my 128k after the RIFA exploded, and was hoping to gain some knowledge because according the list of caps on this Google doc: https://docs.google.com/spreadsheets/d/132RwzC8HM5ask-BdY_31txErOCwJDSkz099GY2XLpE0/edit?usp=drivesdk

The caps used are different than what's on my board. The capacitance is the same, but the voltages on some, such as C1, is 25V on my board vs on the sheet it's 100v. Should I follow what's on my board? Or follow the sheet since a higher voltage capacitor shouldn't really make a difference, right? I've also ordered a new flyback transformer just in case.

 

[LaPorta]

25V was probably the original spec, and was probably underrated. Unless there’s something specific I am unaware of, replacing caps with higher voltage rating is actually helpful because they will be more tolerant of voltage increases and last longer. In addition, I’d look for high temp rated (105 degree) caps for the analog board on a 128k-Plus due to the lack of active cooling.

 

[davidg5678]

The sheet likely lists higher voltage capacitors than what is on your board, because the higher voltage parts may be easier to find or cheaper that way. In general, if the voltage is higher than the original capacitor, it does not make a big difference. If the capacitance is higher, this may cause issues and change the behavior of a circuit. I would recommend following the sheet's instructions.

 

[rushfan82]

Will do. Thank you all.