Hello all
I have a JL Hood power amp built from kit in late 80s. It has Hitachi K135/J50 MOSFET pairs
The second speaker protection relay failed for the second time (the kit came with two relays and I managed to find the spare one) but looks like when it failed it shorted the output of one of the channels, as there is now -72V on the LS output.
1. Can I assume that the MOSFETS are fried good and proper, and
2. Is there anything I can use to replace them.. ? There is no other visible signs of damage and power supply fuses are intact.
thanks for any quick advice
PD
I have a JL Hood power amp built from kit in late 80s. It has Hitachi K135/J50 MOSFET pairs
The second speaker protection relay failed for the second time (the kit came with two relays and I managed to find the spare one) but looks like when it failed it shorted the output of one of the channels, as there is now -72V on the LS output.
1. Can I assume that the MOSFETS are fried good and proper, and
2. Is there anything I can use to replace them.. ? There is no other visible signs of damage and power supply fuses are intact.
thanks for any quick advice
PD
MOSFET's
Hi,
If your MOSFETs are shorted out, the fuse HAS to blow. On the other hand you could have a breakdown of a smaller transistor in the driver or predriver stage which is causing the output to sit at -72 volts.
Your relay must be opening when there is a fault. So maybe it has opened just because of the -72 volts and there is nothing wrong with it.
You will have to check out collector / emitter or drain/source resistance with a meter with the power down on the amp. Check each transistor from output to input and compare it with the similar one on the other channel. I guess you are not very experienced at trouble shooting.
In fact do a base/emitter , base collector , and collector/emitter check . Even if you do not know which lead is which you have only 3 leads on each device and you can pick them in pairs ( for a start). Compare with the same device on the other channel. and let us know.
By the way - if you have -72V on the LS terminals, the speaker (woofer) must be fried. Enjoy your dinner ! Can you smell burnt wire at the woofer dust cap ? It stays a long time ! You should have also "heard" it when it went "Blam".
cheers.
Hi,
If your MOSFETs are shorted out, the fuse HAS to blow. On the other hand you could have a breakdown of a smaller transistor in the driver or predriver stage which is causing the output to sit at -72 volts.
Your relay must be opening when there is a fault. So maybe it has opened just because of the -72 volts and there is nothing wrong with it.
You will have to check out collector / emitter or drain/source resistance with a meter with the power down on the amp. Check each transistor from output to input and compare it with the similar one on the other channel. I guess you are not very experienced at trouble shooting.
In fact do a base/emitter , base collector , and collector/emitter check . Even if you do not know which lead is which you have only 3 leads on each device and you can pick them in pairs ( for a start). Compare with the same device on the other channel. and let us know.
By the way - if you have -72V on the LS terminals, the speaker (woofer) must be fried. Enjoy your dinner ! Can you smell burnt wire at the woofer dust cap ? It stays a long time ! You should have also "heard" it when it went "Blam".
cheers.
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