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WHAT WOULD CAUSE JC-1 MONOBLOCK TO SELF DESTRUCT?

Hi all,
I own Parasound Halo JC-1 monoblock amps, and have never had any reliability issues at all with them.
I have a friend, however, who had a JC-1 monoblock to literally self-destruct.
He said he was listening to it at normal levels, and heard a loud pop that almost sounded like a firecracker went off, the amp went completely dead, and the smell of toasted components filled the air.
He shined a flashlight through the top cover and said that it looked like at least 8 to 10 of the black square Sanken transistors mounted on the sides of inside of the amp, on the heat sinks, had literally blown to pieces!
He said the Sanken devices were still there, but the centers of many of them had literally blown out.
I would assume that these square black Sanken devices are the output transistors?
He checked the power cord, speaker cables, speakers, interconnects, etc., for short circuits and found nothing!
Has anyone else out there had this to happen to their Parasound Halo JC-1 monos, or any other amp before?
What would cause such an incident to happen?
Any answers, ideas, or help would be greatly appreciated.
Thanks a million!
Angela
audio_girl
bignerd100
515 posts
 
The Parasound amps do have a protection circuit for extreme low impedances (as in a damaged speaker). This will turn off the unit before blowing up (usually). If your buddy blew it up once then there are probably parts that sustained damage but tested ok at Parasound. THese parts were likely starting to give out before the thing finally blew up (again). It has been my experiance that once an amp has been blown up it will never be the same unless you replace everything inside the chasis (in which case you might as well buy a brand new unit).

I guess that the 10-15% discount from retail that the average retailer is willing to give looks good after buying used, repairing used, then having to decide if repairing used is worth it the second time. Not trying to add insult to injury but sometimes it is better to drink fresh beer than second hand champaign.

Sincerly, good luck to your buddy. Having big $$$ go up in smoke is tough.
seadogs1
104 posts
 
Perhaps it's time for Mr. Curl to enter this. I too have the shut down problem for seconds at a time then everything is normal. I think it may be connected to the protection circuit of the amp except there is no reason it should be kicking in. Any thoughts by John would be much appreciated.
audioengr
3,282 posts
 
I've repaired some of these type problems. If the amp is shutting down intermittently, there is at least two reasons:

1) there is excessive DC offset on the input to the amp
2) there is excessive bias current to the output transistors - this can be caused by a failing output transistor or an out of adjustment bias pot
bpwalsh
1,213 posts
 
Seadogs1, I suggest you contact your dealer and/or Parasound as mentioned above to discuss problems you may be experiencing. John Curl does not visit this website and rarely gets involved in service matters. Tony or Bob can help you.
audio_girl OP
91 posts
 
Audioengr,
What would cause excessive DC offset on the input to the amp?
How can that be resolved?
My friend also said that sometimes when he would cut his house lights on or off, the amp would shut off for 3 or 4 seconds, the halo light would turn red, then it would come back on and resume normal operation.
His house lights and appliances are on different circuits than his JC-1's.
What would cause this?
Thanks again for your excellent responses.
Angela
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