| Electronics > Beginners |
| Question about the function of a capacitor in a circuit |
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| fedaalis84:
I am going to do a good cleaning of the board and see what I get. Without IC700 in, I'm pretty sure there should be ZERO voltage on any of the bases... Edit: Or maybe some negative voltage from the protect circuit like you say. |
| fedaalis84:
I am using some cheapo water soluble flux I got cheap on Amazon. Which I've read is maybe the worst type of flux if you don't clean it sufficiently, leaving behind a soapy, conductive residue if incompletely cleaned. |
| fedaalis84:
I tested with a DC6V power supply, and current is leaking, from seemingly anywhere on the board to the bases for both transistors on the right channel. It does not leak to the bases on the left channel. Putting power at the biasing circuitry on either side gives similar voltage and current on both sides. So I suspect you're right, and too much flux and improper cleaning have caused some leaky current. I tried cleaning the board thoroughly with distilled water (my flux is water soluble and I have no deionized water on hand), followed up with 50% ISO (again, not a great option, but all I have on hand). The board is drying, but we'll see where that gets me. |
| fedaalis84:
Still issues on right channel after drying. Same deal. 0.6V on left channel, no current. Almost the positive rail on the right, about 6 microamps. Interestingly, one of my 6800uF filter caps is reading -70 to -80 microamps on the top metal part of the cap. The other 6800uF cap (and all other caps on the board) read 0 current. I also read -40V on the top.... that sounds kind of, not good.. |
| xavier60:
Although there should be no leakage, it is not enough to cause problems with the output stage biasing. Leakage around IC700 might cause DC offset problems, but will not damage the output stage. Leakage could affect the protection circuitry directly. |
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