JL Audio 1000/1 No DC voltage at speaker terminals ref ground.

[kds9591]

Have a JL 1000/1 Rev 8 with no DC voltage on the speakers terminals as measured from ground. Should be approximately 57-60VDC. Idle current is also low @ 2.2 amps. Typical is 3.5-3.7 amps.

Other voltages measured in output section.
Top of resistors- component side.
R803 115VDC
R804 0VDC
R805 57.5VDC
R806 57.5VDC
R807 57.5VDC
R808 115VDC
R809 57.5VDC
R810 57.5VDC

Rail jumpers
C00P5 0VDC
C00P6 0VDC

Any insight, ideas or tips greatly appreciated, thanks.

 

[Old'n'Cranky]

Wouldn't DC on the speaker terminals be exactly what you Don't want ??

 

[Perry Babin]

Post #2:
The DC (1/2 rail) is on BOTH speaker terminals, so 0v across the speaker.

Post #1:
If you apply remote then remove it after a second or so, do you see any drive pulses on the gates of the output FETs? The drive should be present for about 15 seconds.

 

[Old'n'Cranky]

Ahh ok so fully floating outputs. Gotcha. Ta Perry...

 

[kds9591]

Solution- conclusion.

There were no drive pulses on the gates of the output MOSFETs and no input pulses on the input for the TC4420 driver ICs. Supply voltage on pin 8 both ICs 10VDC

I traced the input source back to the ICs 513 and 516 (74HC112) and measured the supply voltage at pin 16 @ 0.5VDC should be 5VDC. Resistance to ground from pin 16 measured low about 15 ohms. Replaced those two ICs but still had a problem. Supply voltage still measured low. I knew there was another IC using the same 5VDC supply and dragging it down. Resistance to ground from pin 16 only measured only slightly better 26 ohms. I know several ICs use the 5VDC supply so I left the amp on for a few minutes hoping the one with a internal short would get hot, took the power off, removed the top board and sure enough U509 (74HC132) was very hot.

Replaced U509 and the amp has now has output and 57VDC on both sides of the speaker terminals- ref. ground.

The amp originally had a distortion problem, and a 100 ohm resistor on one of the driver boards was found open and replaced. The amp played fine for about 5 minutes then lost output and the DC voltage on the speaker terminals. After troubleshooting I found the problems above. Unusual failure.

Thank you Perry.