Jbl PB12 powered sub woofer

First try to find the source of your problem. The easiest way would be to try your sub with a different audio source to see if the problem still occurs but is sounds more like there's a problem with the receiver.

So when you power on the sub and put the rca cable into the amp do you get red light only - never goes green or does it flash ?

You can download the service manuals here and read the service bulletin and check per manual.
http://manuals.harman.com/JBL/HOM/Service%20Manual/PB10%20sm.pdf

http://manuals.harman.com/JBL/HOM/Service%20Manual/PB12%20sm.pdf

Hopefully the ClassD module is not bad.
This is what I have done to my: http://s807.photobucket.com/albums/yy352/budm/JBL%20PB-12%20mod/

Service manuals: http://manuals.harman.com/JBL/HOM/Service%20Manual/PB10%20sm.pdf
http://manuals.harman.com/JBL/HOM/Service%20Manual/PB12%20sm.pdf

My ClassD module shorted out (buzzing sound/blown fuse) and not availabled any more so this is what I did: http://s807.photobucket.com/albums/yy352/budm/JBL%20PB-12%20mod/
I would suggest to buy new one.

these a internal power control board defective, send to repair

More likely to be the Class D power amp module, but you should look through the service manual to make sure all the parts are installed correctly. My PB10 AMP module went out and you cannot get one anymore.
http://manuals.harman.com/JBL/HOM/Service%20Manual/PB10%20sm.pdf

yes it can be repaired. but i need more details on this...

These subs have had many problems, all associated with the amplifier section. PB 12's with an "M" as part of the ser. no. were assembled in Mexico and these are the ones with the amp problems. JBL fixed mine and sent it back no charge, BUT it cost me nearly $100 to send it to them in the first place. I have another one that has had no problems at all. Try sending it back for repair. At best you'll get a rebuilt unit back, at worst a substantial discount from the company for a new sub.

I had the same problem...replaced the C42 capacitor with one that I got from RS...fixed everything and all is well again. I only have moderate soldering skills, too, so if I can do it, so can you

exactly......I bought a Klipsh