68kMLA Classic Interface

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Quadra 610 - C54 and C33
Posted by: betaporter on 2023-08-17 15:31:02
I'm trying to restore a Quadra 610 with obviously failed caps. I've replaced the captors, but no boot, not chime, etc.

While poking around on the board I noticed that the positive pad on C53 and C33 are connected to ground. Is that normal?

And, I'm something of a noob to the hobbyist electronics - if this is purposeful, what's the purpose of connecting a capacitor's positive lead to ground?
Posted by: Phipli on 2023-08-17 15:35:09
I'm trying to restore a Quadra 610 with obviously failed caps. I've replaced the captors, but no boot, not chime, etc.

While poking around on the board I noticed that the positive pad on C53 and C33 are connected to ground. Is that normal?

And, I'm something of a noob to the hobbyist electronics - if this is purposeful, what's the purpose of connecting a capacitor's positive lead to ground?
It's normal for the positive to be connected to ground if the negative is connected to the minus rail. Because -12 is more negative than zero.

I don't have a board to hand to check which caps are connected to -12v. But -12v is the end pin (closest to the front) on the connector. Check if that pin is connected to the other side of the caps you're looking at.
Posted by: betaporter on 2023-08-17 20:35:27
It's normal for the positive to be connected to ground if the negative is connected to the minus rail. Because -12 is more negative than zero.

I don't have a board to hand to check which caps are connected to -12v. But -12v is the end pin (closest to the front) on the connector. Check if that pin is connected to the other side of the caps you're looking at.
Ha, you are right. The other side of the cap in question is connected to -12v from the PSU. Thanks for the explanation!
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