Fosgate 1000a2 with blown output

[81300sd]

TH1 is 4.95 and .65

TH2 is 4.95 and 4.95

 

[Perry Babin]

Remove TH2 from the circuit.

The amp should power up. Take the normal precautions that you would when powering up an amp that you don't know is in good working order.

 

[81300sd]

Ok, it powered up. I suspect one of the resistors is bad that is inline with that thermistor.

Probably should check out d12 too.

Do you happen to know what the part # of that thermistor is?

 

[Perry Babin]

I don't know the part number of the thermistor. If it's defective, Rockford may have a replacement.

Measure the resistance across the thermistor. If it's ~10k ohms, it's likely OK. If you heat it and the resistance goes down, it's almost certainly OK.

 

[81300sd]

Thermistor is confirmed dead. Getting about 3.5 ohms on the dead one and about 8600 on the good one.

 

[81300sd]

Hooked it up to the car. I have limited output and the previously dead side is very noisy. I suspect LM317 to be bad as the voltages are spiking all over the place on it. I have some so I think I will change it just to be sure its good.

Just realize I never changed Q321 and Q322 so I will change them also and see what it does.

 

[81300sd]

That didn't do it.

Just testing it. For a minute it was clean sound then it started crapping out.

Checking U6 and U8 middle leg(mur1610ct, mur1610ctr)

When it is crapping out I have 0 volts on the middle leg of u6 and ~108v on the middle leg of u8, something is shorting.

 

[Perry Babin]

Are you sure that no outputs are shorted?

 

[81300sd]

No I am not sure, but all that I am testing looks good. Maybe I am not testing it right.
Rail voltage on the irf9640's is ~108v and 0 on the irf640's

Output voltage is 54v

 

[81300sd]

Not sure if this is important at all, but I noticed when powered up, the first 5-10 or so it seems fine, then it goes bad.

 

[Perry Babin]

Does the output voltage slowly go from 0v DC to 54v DC?

If you push on the board (with an insulated probe), does it make a difference?

 

[81300sd]

Yes, it jumps to about 22v then floats around there for a bit then up to 54, then it will come back down into the 30's and back up.

Pushing on the board didn't seem to affect it.

 

[Perry Babin]

Remove D305 and D307 from the circuit. Be careful, the amp may draw excessive current.

Earlier, I gave you a list of protection circuit parts to check but I listed the 200 series parts. Did you catch my mistake or did you check the 200 series parts instead of the 300 series parts?

 

[81300sd]

No, I caught it. I will remove them.

 

[81300sd]

D305 and d307 removed. No change

 

[Perry Babin]

When you measured the DC on the output, where was the black probe?

If it was not on chassis ground, check it again. I need to know if the voltage swings positive or negative with the black probe on chassis ground.

 

[81300sd]

It is -54v measured on the right side - terminal using chassis ground.

 

[Perry Babin]

What is the DC voltage on the terminals of Q324 and Q325?

Black probe on chassis ground.

 

[81300sd]

Q324
13-14v, floats all around

-6.41

-.20

Q325

-.20

-16.7

-17.16

Those are in CBE order, or 321.

 

[Perry Babin]

Do the same thing for Q306 and Q307.

Are you 100% sure that you installed the correct parts in all locations?