JL Audio 500/1

[Perry Babin]

Does it look like the output filter inductor has overheated? Look carefully.

 

[mike49504]

It appears to still look new no signs of overheating

 

[Perry Babin]

Recheck the outputs.

Did you check the drive signal on the gate pads of ALL 4 outputs?

 

[mike49504]

Ok back to this amp..

I just bought a new probe for my scope ..

I get no drive signal ( square wave) at any of the gate pads for the outputs..

 

[Perry Babin]

Post the DC voltage on all pins of all 4 outputs.

 

[mike49504]

Q504

Leg 1:0.3
Lrg 2:82.0
Leg 3:0.6

Q505

Leg 1:1.28
Leg 2:0.6
Leg 3:0

Q506

Leg 1:0
Leg 2:0
Leg 3:0

Q507

Leg 1:0
Leg 2:82.2
Leg 3:0

 

[Perry Babin]

What have you done to the amp other than installing the outputs and removing the jumpers since you saw 4 good drive signals?

 

[mike49504]

Nothing at all..

 

[Perry Babin]

Do all of the audio op-amps have positive and negative supply voltage?

Is the amp in protect mode?

Do you see a pulse of DC on any of the speaker terminals when you power it up? Have the scope probe on the speaker terminals when you apply remote and continue watching for about 10 seconds after applying remote voltage.

 

[mike49504]

On pin 4 of all op-amps i get 0.62 volts

On pin 8 of all op-amps i get 1.28 volts

Protect light is not on but the low ohms light is on all the time along with the power light..


On both + speaker terminals i get 0.08 volts on start up

On both negative speaker terminals i get 0.66 volts on start up

 

[Perry Babin]

The small square transformer in the center of the board produces the preamp voltage. Do you have a square wave on the tab of the transistor that drives that transformer?

 

[mike49504]

No

 

[Perry Babin]

Post the DC voltage on the 10 pin connector.

Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:

 

[mike49504]

Pin 1: 5.04
Pin 2: 0.12
Pin 3: 13.88
Pin 4: 0
Pin 5: 0
Pin 6: 11.84
Pin 7: 0.26
Pin 8: 11.63
Pin 9: 10.78
Pin 10: 0

 

[Perry Babin]

There is a 5.6v SMD zener diode (SOT-23 case) near the narrow end of the preamp board. What DC voltage do you read with the black probe on bottom left pin, red probe on top pin.

 

[mike49504]

5.70 volts

 

[Perry Babin]

Are you sure that the voltage on pin 4 is 0v?

 

[mike49504]

i get 5.70 volts on pin 4 now

 

[mike49504]

Must have slipped with the probe cause now i burnt that diode out..

I have a 6.8 zener diode would that work for now for trouble shooting?

 

[Perry Babin]

Probably. I've seen the amps work with a wide variation in voltage there.

After replacing it, check the voltage on pin 4 again.