Rockford Fosgate BD15001

[seankane]

Hello again Perry. I recieved this amp and it would not power on just pop the fuse. Some of the output fets were shorted so I replaced them all. Same thing pops the fuse. If I disconnect Q101, Q102, Q103, Q12 the amp will power up fine. Any thoughts??

[Perry Babin]

I think this will be easiest to troubleshoot with DC.

Wire a pot (virtually any value 4.7k or greater will work) like the one shown in the attached photo. Connect it to the op-amp as shown in the other photo.

Remove R31 and R35 from the circuit. Set the pot to the center position before applying power. Rotate the pot about 90° each way from center (don't go to the end of rotation either direction).

When you do this, the DC voltage (measure with multimeter, not the scope) should go from positive 10v to negative 10v. Place the black probe on the source leg of the outputs and the red probe on the gate leg.

Check Q107 and Q104.

[seankane]

Ok my pots are 6 pin like the one you shown in pic but all in a straight line. Its a treble pot 5k for a DSM punch amp. How do I know which legs to use??

[Perry Babin]

See attached.

[seankane]

So which pair do I use? Should I use the A high A low and A wiper to the LM6171 or should I use the B high B low and B wiper to the LM6171. Not 100% sure which wires got to pins 2, 4, and 7 as you have shown on the LM6171.

[Perry Babin]

To make it simple, use the yellow ones. They're in essentially the same order as the one with two rows of pins. The high and low are interchangeable. The wiper goes to pin 2 of the op-amp.

[seankane]

Ok so it does not matter which pin 4 or 7 I wire the high and low to?

[Perry Babin]

No.

[seankane]

Originally Posted by Perry Babin

I think this will be easiest to troubleshoot with DC.

Wire a pot (virtually any value 4.7k or greater will work) like the one shown in the attached photo. Connect it to the op-amp as shown in the other photo.

Remove R31 and R35 from the circuit. Set the pot to the center position before applying power. Rotate the pot about 90° each way from center (don't go to the end of rotation either direction).

When you do this, the DC voltage (measure with multimeter, not the scope) should go from positive 10v to negative 10v. Place the black probe on the source leg of the outputs and the red probe on the gate leg.

Check Q107 and Q104.

Hey Perry just got back from dinner. I built the test tool and installed it as requested and powered up the amp after removing R35 and R31.

Upon rotating the pot as you said checking Q104 and Q107 they both switch from positive to negative as you said. The DC voltage was 9.74 vdc.

What next?

[Perry Babin]

Generally, this rules out all driver issues. Do you read infinite resistance (OL) if you measure from the gate leg of the 3415s that you have out of the circuit to the other legs of each individual 3415?

If you desolder the gate leg of the 6215s working with this group of 3415s, do you also read OL from their gate to each of the other legs of each individual transistor?

Did you check the gate resistors for this group of 8 transistors?

Did you replace this group of 3415s and 6215s?