Can you explain that a little more? Are you saying that since the inside (where the male prong of an rca wire goes into) and the outside of the plug should never be the same. In other words, even though there shouldn't be high voltage on either, the fact that there is on both means that the problem, whatever it is, is effectively bridging the signal circuit for the outside and the inside of the input plug, and this bridging means the two (normally separate) circuits have been compromised?
And if they are compromised (who cares wire), the sub is lunched?
And if they are compromised (who cares wire), the sub is lunched?
Okay I've re-tested.
1. The outside of the input is definately line voltage (black probe of my multi-meter to the ground in an electrical outlet). I checked an outlet with my multi meter and got the exact same reading.
2. When I check the voltage from the outside of the input to the inside, I get a very small voltage reading and the fairly quiet speaker hum.
3. When I check the inside of the input with the red probe and the other lead of the probe to the ground on the electrical outlet (same as number 1 but checking the inside), I get a very loud hum and the meter needle is heading fast for 110v but because the sound is so loud I didn't hold the connection.
1. The outside of the input is definately line voltage (black probe of my multi-meter to the ground in an electrical outlet). I checked an outlet with my multi meter and got the exact same reading.
2. When I check the voltage from the outside of the input to the inside, I get a very small voltage reading and the fairly quiet speaker hum.
3. When I check the inside of the input with the red probe and the other lead of the probe to the ground on the electrical outlet (same as number 1 but checking the inside), I get a very loud hum and the meter needle is heading fast for 110v but because the sound is so loud I didn't hold the connection.
There was another JBL sub, or maybe it is this same model that one of the things the shop was supposed to check before sending it back to the customer was for any voltage leakage to the frame or shield of the RCA connector. If there was voltage present there was a component that was supposed to be changed on the amplifier board.
I've managed to trace a problem like this to a faulty transformer, which was leaking mains voltage from the primary. Whereas it wouldn't blow anything up, the entire chassis system was at full line voltage (and we have 230 volts here).
The transformer had to be replaced, since even after earthing it the transformer was looking into a virtual short-circuit.
We also had a situation with a computer system that was not connected to mains earth at any point, and the casing and exposed metal parts were all at 230 volts. The computer itself operated fine, and the problem was spotted only when the owner tried to plug in a USB drive.
In the second case, earthing the system properly fixed the problem.
Do any of your equipment have a safety ground or are they all the 2-pin type?
The safest is to send the sub in for repair, there may be a contact at some point to the chassis - a frayed or loose wire, a broken washer, a screw gone astray, or simply a leaky/defective transformer.
The transformer had to be replaced, since even after earthing it the transformer was looking into a virtual short-circuit.
We also had a situation with a computer system that was not connected to mains earth at any point, and the casing and exposed metal parts were all at 230 volts. The computer itself operated fine, and the problem was spotted only when the owner tried to plug in a USB drive.
In the second case, earthing the system properly fixed the problem.
Do any of your equipment have a safety ground or are they all the 2-pin type?
The safest is to send the sub in for repair, there may be a contact at some point to the chassis - a frayed or loose wire, a broken washer, a screw gone astray, or simply a leaky/defective transformer.
Naughty, posting the same question twice
http://www.diyaudio.com/forums/showthread.php?s=&threadid=108152
http://www.diyaudio.com/forums/showthread.php?s=&threadid=108152
Thanks good suggestions.
And to the double posting. At the begining on this thread, I was suggested to move the posting, which I did - but then we continued here and I didn't know how to cancel the thread.
Thanks for everyone brain power and good thinking. I'm giving up and finding a pro to look at it.
And to the double posting. At the begining on this thread, I was suggested to move the posting, which I did - but then we continued here and I didn't know how to cancel the thread.
Thanks for everyone brain power and good thinking. I'm giving up and finding a pro to look at it.
Sensible suggestion!
A DMM will read a voltage on almost anything floating.
Connect a household lamp (bulb) between the RCA outer and the ground socket, then measure across that. It's a fair bet that there will be (virtually) no reading.
Take care to do this safely, though - i.e. assume that there really is significant HV on those sockets until proven otherwise!
FOUND It! I found out the entire backing plate was charged so I unscrewed the circuit board from it and it was still hot. This left the transformer and some little do-hicky. It was the do-hicky.
Here's my best description: It about the size of a dime in diameter, with a sandwich of a metal disk on bottom and then a plastic disk on top. All total, it's about 1/2 inch high with two male spade connectors on top. Two black wires from the transformer hook to these connectors. As I say, the do-hicky is attached to the backing plate with two screws. (I can see a tiny burn through on the side of the metal disk).
It says "Selco OA140" Anybody know what it is?
And thanks to the moderator for the help. Thanks to you all.
Here's my best description: It about the size of a dime in diameter, with a sandwich of a metal disk on bottom and then a plastic disk on top. All total, it's about 1/2 inch high with two male spade connectors on top. Two black wires from the transformer hook to these connectors. As I say, the do-hicky is attached to the backing plate with two screws. (I can see a tiny burn through on the side of the metal disk).
It says "Selco OA140" Anybody know what it is?
And thanks to the moderator for the help. Thanks to you all.
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