JL Audio 500/5

[cajones65]

I have this JL Audio 500/5 Rev 1 it plays on rear and sub. However it doesn't play on Front left or right. Moved selector switches and many combinations to no effect. All LED's on the boards are lit. I did clean all the switches before I got the rear and subs to play.

There are no shorted or open FET's. What am I missing?

 

[cajones65]

After I wrote this post, I don't know what happened. I turned the amp back on and now the "Low Ohm" light is lit and there is no LED's on any of the boards lit. What the h%$# did I do.

 

[Perry Babin]

Did you recheck for shorted FETs?

 

[cajones65]

I did, I believe that I found the problem before I put it away for the night. There was a loose piece of solder between the rectifier middle and outer leg. Must have happened when I was removing old solder from 33 ohm resistor and resoldering it.

It then set there with power applied and not pulling in current at all... Then I had all my LED's back on and the rear and sub channels still working. Not the front though.

 

[cajones65]

What is in common with both left and right front outputs?

 

[Perry Babin]

I don't know. Maybe someone else knows.

Are you getting signal to the muting transistors (or Cx13) for the front driver boards?

 

[cajones65]

I am not getting a signal to the muting transistors

 

[Perry Babin]

Just to clarify, Did you have 2 speakers on the dead channels and signal driving those channels while operating all switches in all combinations to see if ANY sound (music, static, noise) ever came from those 2 channels?

 

[cajones65]

Didn't have music or static, I heard a click/pop when I moved the "Filter Mode" switch through a speaker. I didn't have 2 speakers hooked up at one time. I did it channel by channel.

 

[cajones65]

Update all channels are now playing. The 2sp/4sp switch had a broken solder on a leg.

 

[Perry Babin]

It's good that you found it. To have a bad solder connection on a double sided board on a component that is rigidly held into the board by its supports is very rare.

 

[cajones65]

Well guess what, once I put the amp back together to truly test it. I noticed that with only power applied and no remote, I had a small current flow. When the amp was working and no remote, I had no current flow. So I applied remote, Low Impedance light comes on and no LED's lit up on any of the driver boards. Hence I am now back to square 1.
What causes the Low Impedance light to come on?

 

[Perry Babin]

I think the LED may be triggered by multiple circuits in this amp. If I'm not mistaken, there are 3 main circuits (front/rear/sub).

Is it possible that you have a broken leg on one of the output FETs? A broken gate leg can cause intermittent problems like this.

 

[cajones65]

I am pulling it apart now and looking.

You are correct, it does have a Front, Rear, and Sub

 

[Perry Babin]

While the FETs are still clamped to the heatsink, see if you get a pulse of DC (measured directly across the speaker terminals).

 

[cajones65]

Found no broken legs on FETs.

Will clamp it back to heat sink and test for voltage.

 

[cajones65]

On the sub speaker terminals, I am getting 56vdc on sub. on the Front I am getting 96mv and rear 71mv. As I was checking the voltages again, the amp started working and all voltages dropped, Subs to 14mv front 2.6mv and rear 12mv.

 

[Perry Babin]

Start pushing on various components and various areas of the board with a non-conductive probe (dowel, bamboo skewer...). Can you find anything that causes the amp to malfunction when doing that?