Carvin LM15 Powered PA Cabinet Protect Circuit

[gerryt]

I have a Carvin LM15 powered PA cabinet where the protect circuit light stays on when the unit is powered up. I have tested the woofer and tweeter to be sure they are working and have continuity. I have not been able to find a schematic for this unit and have contacted Carvin to see if they can send me one. Any suggestions about what might some of the likely causes might be that I could look for? I do not have formal electronics training but I am learning and appreciate any suggestions. My semi-retirement project is to take in unwanted and or not working music gear - audio, pa, instruments etc, fix them up and sell them and donate the $$ to charity. http://www.gearforgood.ca This forum was very helpful for the diagnosis and fix of my QSC amplifier a while back.

 

[Martaine2005]

Sounds like you may have a short on the output.
Disconnect the speakers and see if the protection circuit still kicks in.
If it does, check the output transistors.
Does this unit have output for more series/parallel speakers?.
If so, the amp overheated or there was an impedance mismatch.

Martin

 

[gerryt]

Thanks for your reply. The unit has XLR output for another powered unit, but does not allow for unpowered speakers to be added. I disconnected the speakers and the protect circuit still is on. I will check the output transistors.

 

[gerryt]

Yesterday when I was doing some testing on this unit, it was unplugged but I got a mild shock when touching the large heat sink and fan assembly. The filter caps were still holding some current. But I am wondering why the heat sink would be transmitting some current. I have uploaded a schematic for anyone who might be interested in this.