Crate BV6212 Diode Shorting

[robvb68]

Anyone got an idea what might cause D6 and D7 to short out as soon as I put them in the board? There were some bad resistors in R42 and R43 which I have replaced, along with some others on this board. As soon as I solder them in, they test as being shorted out.

[gtrplayr1976]

I always thought you had to test diodes with one end disconnected ? Have you tired powering it up with a light bulb limiter ? I can't get the attachment to open for some reason. Someone else might be a better help.

[Enzo]

The link is dead for me too. No doubt it was posted before and needs to be zipped or resized.


As to unhooking one end, that all depends on what you are testing, what sort of circuit it is in, and what you are testing it for.

If you want to know if something is shorted, just measure it where it sits. There is no circuit that can mask a shorted component. Parallel circuits can make it LOOK shorted, THEn we lift one end to be sure. But if it is shorted, we don;t need to unhook it to find out. Isolating a part then certainly makes the readings more certain, but if I am looking for continuity or something, the value of the part is less important at that moment than whether it is broken in half or not.

Some transistor circuits have pairs of transistors wired back to back, and you have to separate them to get real junction drops. But a simple gain stage, I check then in circuit all the time.

[Enzo]

Oh, and just a hunch, if D6,D7 are high voltage rectifiers, then something downstream of them is likely shorted to ground - a power tube, a flyback diode, an output transformer, a filter cap, a bit of hardware stuck under the board, etc.

[gtrplayr1976]

I thought I had a BV60 schematic ,but I only have the 50 ,and the120. D6 ,and D7 on the 50 are connected to the FS jack. On the BV120 D6 ,and D7 are part of a bridge rectifier circuit on the hv power supply.

[robvb68]

I think this one will work.

[gtrplayr1976]

I think this one will work.

That's more like the BV50.

[robvb68]

I also noticed that now R42, right before the diodes in question, which I just replaced is now reading funky like it was before I replaced it. R5 and R102, which I also replaced due to funky readings are also now reading weird again.

[gtrplayr1976]

I also noticed that now R42, right before the diodes in question, which I just replaced is now reading funky like it was before I replaced it. R5 and R102, which I also replaced due to funky readings are also now reading weird again.

I've had resistors read off when they are in the board ,and when I take an end loose they read fine, so they may be reading back through another component.

[robvb68]

I've had resistors read off when they are in the board ,and when I take an end loose they read fine, so they may be reading back through another component.

When I first put them on and tested them after I soldered them in they read like they should, so something is certainly going on. I have a duplicate one of these amps, they read "off" on it too, but that amp also has a little bit of noise.

[gtrplayr1976]

When I first put them on and tested them after I soldered them in they read like they should, so something is certainly going on. I have a duplicate one of these amps, they read "off" on it too, but that amp also has a little bit of noise.

I get weird readings when I try to read a resistor paralleled with a cap. Looks like 5 ,and 102 are all paralleled with C1 ,and C44. R42 is series with other resistors.

[robvb68]

Actually, after looking at the other amp, the diodes actually read the same way on that one too, they read as if shorted, so maybe that is how they are supposed to read with a bench test, although the other diodes on the board read like they should. I do know that on this particular amp, before I replaced the diodes I had a horrible hum, and one diode tested as it should, and the other tested as shorted. I replaced them both and the horrible hum was gone, but there is still some hum.

[robvb68]

I get weird readings when I try to read a resistor paralleled with a cap. Looks like 5 ,and 102 are all paralleled with C1 ,and C44. R42 is series with other resistors.

Yes, those are paralleled with those caps, so maybe after being attached a short period of time the reading changed. As I said, the other amp also reads that way.

[gtrplayr1976]

Actually, after looking at the other amp, the diodes actually read the same way on that one too, they read as if shorted, so maybe that is how they are supposed to read with a bench test, although the other diodes on the board read like they should. I do know that on this particular amp, before I replaced the diodes I had a horrible hum, and one diode tested as it should, and the other tested as shorted. I replaced them both and the horrible hum was gone, but there is still some hum.

I think that is a trait for Crates. I have a VB5310 that hums ,and a BV50 that hums. I think the grounding isn't so great in these.

[Enzo]

If you replaced D6, D7, did you install them the proper direction and did you use 3.3v zener diodes?