Rockford Fosgate Type RF X6

[seankane]

I have this amp for repair. Protect light is lit but not real bright.

U21 has no voltage on pin 7. Does this mean U21 is defective?

 

[Perry Babin]

Do you have positive and negative supply voltage on U21?

Do you have rail voltage?

 

[seankane]

Do you have positive and negative supply voltage on U21?

Do you have rail voltage?

No hardly,

Pin 4: -1.055 vdc
Pin 8: 3.369 vdc

I have only 60 vdc across red and black wires which seems low to me.

 

[Perry Babin]

Are the power supply FETs damaged? Look at the gate and drain waveforms with the scope.

 

[seankane]

The gate and drain signals look terrible, but the FETS do not measure shorted in the circuit.

Im not getting a square wave from the output pins on the SG3526 either.

 

[Perry Babin]

Post a photo of the output signal from the 3526.

 

[seankane]

Here is the pick. Pins 13 and 16 look identical. It seems the amp is only partially powering up. One set of regulators has output the other 2 sets have hardly any. 2 of the rectifiers have 60vdc the other 2 only have 20vdc. I am getting -9.50vdc on alot of the op-amps but only 1-3vdc on the positive side. Only half of the output fets are getting the -9.50vdc and the other half are getting no voltage.

 

[Perry Babin]

Post the DC voltage on all pins of the 3526.

 

[seankane]

1: 4.90
2: 1.320
3: 0.595
4: 0.155
5: 1.775
6: 0.001
7: 0.001
8: 1.765
9: 3.610
10: 2.062
11: 0.003
12: 4.80
13: 0.055
14: 13.65
15: 0.001
16: 0.054
17: 13.65
18: 4.90

 

[Perry Babin]

The voltage from the LM339 doesn't look right. Post the voltage on all of its pins.

 

[seankane]

This one has the revision done for the initial power up issue.

Pins 1 and 2 are soldered together and pin 13 has been removed.

pin 1: 1.776
pin 2: 1.776
pin 3: 13.65
pin 4: 0.095
pin 5: 1.381
pin 6: 4.41
pin 7: 4.70
pin 8: 0.785
pin 9: 0.785
pin10: 4.90
pin11: 8.31
pin12: 0.001
pin13: missing
pin14: 0.001

I posted a pic of the MOD the description of it was included with the copy of the schematic I sent you awhile back.

 

[seankane]

A pic of the MOD.

 

[Perry Babin]

Desolder leg 1 from pins 1 and 2 of the 339. Does that allow the amp to power up?

 

[seankane]

No it does not because pins 1 and 2 are connected by a trace on the board anyway.

 

[Perry Babin]

Do you still have approximately 1.7v on pins 1 and 2?

 

[seankane]

yes

 

[Perry Babin]

If you have a 339, replace the one in the amp. With the input on pins 4-7, the output should be open and pulled up by R19.

There is a chance that the SD pin on the 3526 is causing the problem but the 339 is easier to replace.

 

[seankane]

Should I remove all the mods because R19 is fed from pin 13 which is missing on the lm339.

 

[Perry Babin]

You can leave the leg of the 34064 disconnected.

 

[seankane]

replaced 339 same result.