jl audio 100/1

[Perry Babin]

A j111 is a jfet and will appear to be leaking or shorted unless a bias voltage is applied to its gate. These rarely fail.

 

[Perry Babin]

Did you get this amp working?

I have one in the shop now but it will only be here for about a week (waiting on parts) so if you need help with yours, we should get back to it as soon as possible.

 

[mike49504]

Ok Perry,

I hooked this amp up again and no light still. So I hooked up inputs and a sub to it to see if i got output.

Only thing i get is a loud humming noise on the sub when amp is powerd up

 

[Perry Babin]

Did it hum with no input?

There are 3 resistors near the center of the main board between 6 capacitors. What is the voltage on those 3 resistors?

 

[mike49504]

Its hums with no input hooked up.

The resistors read going from front (closet to inputs) to back

1= 0.50
2=0.70
3=0.10

 

[Perry Babin]

In an earlier post where you listed the voltages for the power supply board and the 10 pin connector, it appeared that the low voltage supply was working. Now it doesn't. Post those voltages again:

PS Driver board
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:

Also post the voltage on the 10 pin connector on the preamp board.

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

 

[mike49504]

Power Supply Driver Board

Pin1= 2.56
Pin2=2.55
Pin3=0
Pin4=0
Pin5=1.00
Pin6=0
Pin7=0
Pin8=.02
Pin9=0.97
Pin10=0.25
Pin11=5.79
Pin12=2.38
Pin13=13.46
Pin14=2.35
Pin15=5.09

Preamp Board
1=0
2= -14.16
3=12.42
4=11.33
5=0
6=13.38
7=0.27
8=0
9=13.18
10=0

 

[Perry Babin]

This would seem to indicate that all supplies are again working. Recheck the voltages on the resistors between those capacitors.

 

[mike49504]

starting with closet to front of the amp

1= 0.50
2=0.71
3=0.10

 

[Perry Babin]

Something's not right. Are you checking the resistors in the yellow rectangle in the attached photo?

If so, the voltages you read there and the ones you posted for the power supply and 10 pin connector don't match. The bottom resistor in the photo is directly connected to the transistor that drives the negative voltage to pin 2 of the 10 pin connector.

Recheck them. Black probe on chassis ground.

You stated that it hums with no input. Did you run all of the switches and pots through their entire range to see if any made a difference?

 

[mike49504]

Ok starting with the closet to front of the amp

1= 14.67 on 1 side -14.15 on other

2= 13.89 on 1 side 14.59 on other

3= 21.59 then drops to 0 withing a sec on 1 side 20.61 and drops to 0 in a split sec on the other

 

[Perry Babin]

Are all of the rectifiers (on the sink) in the circuit?

Do any of the rectifiers have broken legs or solder connections?

Do you have ~115v on two of those rectifiers?

 

[mike49504]

no broken legs

d801 and d802 = 111.7 on middle leg

the other 2 = 56.2 on middle leg

 

[mike49504]

wondering if you know where i should check next

 

[Perry Babin]

What is the resistance (no power applied) from the pin indicated by the arrow and the center leg of D801?

 

[mike49504]

it measure 0.2 ohms

 

[Perry Babin]

What's the resistance from the point indicated in the photo to the center leg of D801?

Does the diode check OK? Pull one lead out of the board and make sure it reads ~0.5v (diode check mode) in one direction and open in the other direction.

 

[mike49504]

ok from arrow to center leg on 801 reads 0.2 ohms

diode reads 0.465 in diode check

 

[Perry Babin]

With the amp on, measure the DC voltage on both sides of the diode (diode back in the circuit). Post what you find.

 

[mike49504]

non stripped side = -0.68

stripped side = 29.52