C13 capacitor substitution 270uF for 220uf? 820-0206-B

L

litriSE

6502
Hi all,

I'm restoring a Macintosh SE with analog board 820-0206-B (630-0147, © 1986/87).

Background: The machine booted fine once with a healthy chime and correct display. During that session I heard a brief fizzle, the screen dimmed, and the floppy icon became distorted. After power cycling it still chimes correctly but the screen is near-black with a squat/compressed floppy question mark icon — suggesting reduced vertical deflection amplitude.

I located and removed C13, which is the original 1987 Nichicon cap (date code H8742). Testing confirmed catastrophic failure:
- Rated 220µF 16V
- Measured capacitance: 53µF (24% of rated)
- ESR: 150 ohms
- The bottom seal had also pushed out with visible electrolyte leakage onto the board

I have Nichicon KZH series 270µF 35V caps on hand, tested at 276.8µF with ESR of 0.25 ohms — excellent condition.

My question: Is 270µF a safe substitute for 220µF at the C13 position on this board? I understand the voltage upgrade from 16V to 35V is fine, and that for a filter or coupling application the 23% capacitance increase should be within tolerance. However I don't have the schematic in front of me and want to confirm C13's role in the circuit before committing to the install.

Any guidance appreciated. The board is otherwise very clean and original for its age.

Thanks, litriSE
 
What is C13's role in the circuit — is it a filter cap, coupling cap, or does it serve a timing function? Replacing with the same is an option and thank you for the quick response - I was hoping for a little more details on the function and if I could replace with a high quality capacitor that I had on hand instead of putting an order together. Thank you nonetheless. litriSE
 
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