JL 450/4 channel 2

Shane73

Member
2016-02-18 1:57 am
I have a JL Audio 450/4 that has issues with channel 2. I bought the amp with the low ohm light on and no sound on channel 2. I pulled the output fets and checked them with a dmm and they checked out okay. When I powered the amp up without the channel 2 output fets the low ohm light went off and the amp played normal on 1,3 and 4. I also cheched the power fets and c3198 driver. All checked out okay. I measured the rail voltage and got 43 volts. Now, the issue seems to be that I am getting 32.6 volts to pin 3 of q203 and q203 but also 30.2 volts to pin 1 of same transistors. This only occurs on channel 2. Channel 1 gets 32.6 volts to pin 3 but no voltage to pin 1 and it works fine. Any ideas. Thanks.
 

Shane73

Member
2016-02-18 1:57 am
I ordered a new set of irf540 to replace the output transistors. Channel 1 now causes low ohm light to come on and the power fets run warm and I end up pulling nearly 50 amps from my power supply. Channel 1 operates at low power fine but distaorts at high power. I pulled out output fets for channel 1 and it runs fine on 3 and 4. Still get good rail voltage on supply line for 1 and 2. Should I replace the power fets and drivers anyways?
 

Shane73

Member
2016-02-18 1:57 am
I placed a known good set of irf540 in channel 2 and still received nothing. What is the small circuit board with the three green leds? Is it some type of driver circuit. It is what is supplying voltage to pin 1 of the fets on channel 2. No other channel is receiving voltage on pin 1 at idle.
 

Shane73

Member
2016-02-18 1:57 am
I ordered new ifr540 for the output fets and 50n06 for the power fets but I don't eant to put the output fets in channel 2 until I figure out what is the issue. I used the output fets from channel 1 on channel 2 just to see if I got any sound at all. It is completely dead, no sound or any output at all.
 

Shane73

Member
2016-02-18 1:57 am
There is 0 votage from the speaker terminals on channel 2. I tried all switches and pontentiometers with the only change occurring when I switched from 1,2,3 and 4 channels to just 1 and 2, I got some type of feedback on channels 3 and 4. They just stated buzzing with no audiable music.