Dead short across a capacitor, help please

elnaldo said:

If you can, remove the capacitor in question, so we are sure you are measuring a short somewhere in the circuit.

I can't check your readings right now, but later today.

But you read a short between the V- and ground, so that's not OK.



Not that easy... Look, from Q709 Gate, there is a dotted line, connecting 2 more circuits, one on top, other at the bottom.

So, many components connected to the -V rail. Try to isolate the different parts.

Click to expand...

Thank you for the help so far :thmbsp:

I was wondering about that dotted line....sigh, I better get checking all those components.

having tested most of the components on the -ve rail i'm still not finding anything faulty...could the problem be with something else?

It could be something mechanical. Some solder bridge or wire in contact with ground.

Do you read Zero ohm, or a few ohms resistance between V- and ground? I ask this because there are several FET transistors around, and they can read "continuity" under certain circumstances. (I never remember how to test them, I always end searching some tutorial on the web)

Try to isolate parts. Or, remove components to test and leave them outside the circuit. You can lift one end of one resistor and isolate a whole part of the circuit. Take notes and picts, and label the components and wires. It's easy to forget where a wire was 1 minute ago.

Study the schematic, proceed step by step, and don't forget the visual inspection and the simple and obvious things . I was 8 months fixing a PCB, but with a better visual inspection I could fix it in 2 hours.

If we start from the top of the schematic (Rec Out Buffer Amp), the -V rail ends at C508, beside Q502. I's say, start removing Q502. And proceed backwards.

Then, at the bottom, the V- goes to C307, bottom-left of the schematic. You can remove that cap too.

Or start at the power supply, removing Q709-D702.

Pay attention while you are there, perhaps you see something causing a short.