68kMLA Classic Interface
This is a version of the 68kMLA forums for viewing on your favorite old mac. Visitors on modern platforms may prefer the main site.
| Click here to select a new forum. | |
| C13 capacitor substitution 270uF for 220uf? 820-0206-B | |
| Posted by: litriSE on 2026-05-22 13:51:37 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 | |
| Posted by: Byrd on 2026-05-22 14:39:47 replace with same, especially when it’s easy to source the exact rating | |
| Posted by: litriSE on 2026-05-22 14:52:57 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 | |
| Posted by: litriSE on 2026-05-22 17:46:42 I think I'm getting close to the answer. It looks like filtering. Opinions welcomed.  | |
| Posted by: luRaichu on 2026-05-22 17:49:41 | |
| Posted by: litriSE on 2026-05-22 19:49:15 Thanks for the reference. litriSE | |
Posted by: Phipli on 2026-05-23 02:18:59I think I'm getting close to the answer. It looks like filtering. Opinions welcomed. View attachment 99119Replace with the same. That is on the input side of the flyback. I don't know for certain, but it feels like changing it might impact the sawtooth shape and distort the display output. It might not, I've not messed with flyback circuit component values, but as others have said, might as well order the right part. | |
| Posted by: litriSE on 2026-05-23 04:35:15 Thank you very much Phipli. I'll put an order together and replace C13 with the designed value... as well as re-cap the rest of the board. litriSE | |
| Posted by: litriSE on 2026-05-23 12:46:34 C13 replaced with 220uf 25V as per designed capacitance value (and went up in voltage). Tested and all good. Thanks for the quick responses. litriSE | |
| 1 |