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Thread: List of Capacitors for Macintosh Classic

  1. #1
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    Default List of Capacitors for Macintosh Classic

    I picked up a Macintosh Classic today but it badly needs a recap. Thing is I can't for the life of me find a capacitor list for the main board.

    Would anyone happen to have a list?

    I really didn't expect this to be so hard to find.

  2. #2

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    7x 47 F, 16V
    1x 1 F, 50V

    You should do the sweep/power board as well. While it has no SMD caps, on mine most did leak anyway. I ordered caps for it yesterday. Let me know if you need a list.

  3. #3
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    Quote Originally Posted by Timo W. View Post
    7x 47 F, 16V
    1x 1 F, 50V

    You should do the sweep/power board as well. While it has no SMD caps, on mine most did leak anyway. I ordered caps for it yesterday. Let me know if you need a list.
    Many thanks for this. I've got the caps ordered.

    From a visual inspection the power board looks fine but as you say it probably needs a recap too. If you have the list, I'd be grateful if you could share.

    I was going to clean and recap the motherboard then take a look at voltages before making a call on the sweep/power board. Thing is I've never done any work so close to a CRT and that HV. I've watched practically all of Adrians videos (Adrians Digital Basement) so I'm fairly confident and it seems that the HV should discharge itself but I do need to get something to check this. I do know a TV repair specialist so I might ask if he has any old HV probes I could borrow.

  4. #4

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    For the power board (rev. A) you need a total of 25 caps:

    5x 1 F, 50V
    1x 4.7 F, 250V
    1x 10 F, 25V
    1x 10 F, 50V
    2x 47 F, 25V
    1x 220 F, 16V
    1x 220 F, 35V
    2x 220 F, 400V
    3x 470 F, 25V
    1x 1000 F, 6.3V
    1x 1000 F, 10V
    2x 1000 F, 16V
    1x 1000 F, 35V
    2x 2200 F, 10V
    1x 2200 F, 16V

    Since you can always use higher-voltage ones, you can combine those with the same capacity to some extent. E.g. just order 5x 1000 F, 35V and 3x 2200 F, 16V.

    The Classic has a bleeder, so the CRT is normally discharged after some hours with no power. HOWEVER, that is only a safty fallback and does not free you from discharging the tube. You have to do this anyway, especially since the bleeder resistor often fails. Follow this video and nothing bad should happen: https://www.youtube.com/watch?v=x1DeMOl_nK4
    Last edited by Timo W.; July 1st, 2020 at 02:09 AM.

  5. #5

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    After watching the video again, I need to make an addition that he does not mention:

    The Mac he uses to show how to discharge the tube has a simple neck plug. Everything he does is 100% correct. However, for compact Macs with a neck board (like the Classic) instead of a simple plug, you need to ground the screwdriver to the metal chassis, not to the upper left lug of the CRT. Otherwise you risk frying the neck board. Likewise, if you use the metal chassis on compact Macs with no neck board, you risk frying the main board (if it is still connected, that is).

    So for the Classic, ground the screwdriver to the metal chassis.

  6. #6

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    Quote Originally Posted by Timo W. View Post
    I ordered caps for it yesterday.
    Got them already. So going to recap my power board today.

    IMG_20200702_131322261.jpg

  7. #7
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    Quote Originally Posted by Timo W. View Post
    Since you can always use higher-voltage ones, you can combine those with the same capacity to some extent. E.g. just order 5x 1000 F, 35V and 3x 2200 F, 16V.
    Higher voltage caps are usually internally different than lower voltage ones, so drifting too far in voltage can cause problems with ESR. Like a 50v cap will have a different and sometimes much higher ESR than say a 10v cap.

  8. #8

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    Link to some serious site stating and explaining this, because this contradics with 99.9% of what even people deep into electronics say. In fact, this is the first time I ever saw someone stating that at all. Now, I would certainly agree that it makes no sense to replace an electrolytic cap rated 6.3V with one rated 250V, because that's quite an extreme anyway - and that's why I clearly said: "to some extent". But for e.g. 35V or 50V instead of 10V, it makes no difference. When comparing data sheets, you'll notice that those with a higher voltage rating can take higher ripple current, which is an advantage, too.

    Besides, ESR won't be an issue in this case. These days, you only seem to get low-ESR caps anyway and the Classic uses ordinary caps. So even in the worst case, the ESR will still be better than that of the old caps used back then.

    Could it be that you are thinking of ceramic caps? Because there, this is partly true. Among other things like temperature, the capacitance of ceramic caps also depends on how close the working voltage is to the rated voltage, so you must use the correct ones. But we are not dealing with ceramic caps here.
    Last edited by Timo W.; July 2nd, 2020 at 11:59 PM.

  9. #9
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    I successfully managed to discharge the CRT, well, I tried it but there was no spark. I can only assume the internal bleed resistor is still working.

    Just waiting on the postman now to hurry up and deliver the replacement caps I ordered!

    The leaking electrolyte is extensive on this board but at least it looks cosmetic only, hope so anyway. Washed it all off and there's just some tarnished pads but the fibreglass pen should make short work of those. I haven't ordered caps for the power board yet. Want to test it before jumping in there. No bulging or signs of leaking so may be OK.

  10. #10

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    Quote Originally Posted by Glen M View Post
    Want to test it before jumping in there. No bulging or signs of leaking so may be OK.
    On my power board, there were no signs of leakage either and the Classic still worked, too. But knowing the caps were 30+ years old, I wanted to renew them anyway. As soon as I had desoldered the first one, that fishy smell came up and the cap was wet underneath. That large cluster of caps at the speaker was particularly bad with 6 of 9 leaked.

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