Rockford Fosgate Power 800.4

[Perry Babin]

Black probe on source of Q110. Red probe on base of Q121. What's the DC voltage?

 

[seankane]

+1.965 vdc

 

[Perry Babin]

Q122 appears to be open.

 

[seankane]

I replaced it with same result still have the -35.67 dc on the bridging terminal

Without Q106 and Q105 in the circuit I had 50 vdc on the bridging terminal.

 

[Perry Babin]

I thought that you had -37 with Q105 and Q106 out of the circuit (post #18).

I assumed that the voltage on the base of Q122 was at or below the voltage on the base of Q121. If that was so, the transistor would have to be open if you read 40 ohms between the gate of Q110 and the emitters of the drivers. The base of the PNP driver can't be that far below the emitter unless it's defective.

 

[seankane]

I did have -37 with Q105 and Q106 out of the circuit until I replaced Q122 then I had 50 vdc. Installing Q105 and Q106 back into the circuit brought it back down to -37 again.

 

[seankane]

A pic of section I am working on.

 

[seankane]

When I recieved the amp there was a jumper wire from the circled areas which allowed Q110 and Q123 to read the same resistance as the rest of the outputs gate to source. The voltage was still present though.

 

[seankane]

R139 to the emitter of Q116

Dont know why but I thought I would mention it.

 

[Perry Babin]

The jumper was shorting the drive voltage to the drivers.

Leave Q105 and Q106 out of the circuit.

When you had 50v, if you touched a dummy load to the speaker terminals, would the amp draw excessive current?

clamp the outputs before trying this.

Do you have any new RCA jacks for the amps like the T20001BD?

Or do you know what they cost from Rockford?

 

[seankane]

I dont get this amp, with Q105 and Q106 out of the circuit I no longer have the 50vdc I have the -37 again. Maybe Q122 is defective again. It reads -4.49 on the emitter and -.966 on the base with Q105 and Q106 out of the circuit.

When I try to hook up a dummy load the amp draws massive current like it has a dead short.

I do not have any new RCA's for that series. I dont know what Rockford charges for them, but I have several used sets that are perfectly fine.

Do you need a set? Just one or both?

 

[Perry Babin]

OK. With Q105/6 out of the circuit, give me the DC voltage on all terminals of Q121, 122, 110, 123. Place the black probe on the negative rail or the source of Q110/123.

Confirm that Q121 is an NPN transistor and Q122 is a PNP transistor. Also confirm that Q110 and Q123 are IRF540s.

I need to order new ones to justify the labor that I'm going to have to charge. I'll check with Rockford.

 

[seankane]

Q110 and Q123 are IRF540's (YES)

Q121 is an NPN (YES)

Q122 is a PNP (YES)

Holding black probe on source of Q110 terminals of Q121 and Q122 read as follows:

Q121

C: 23.18 vdc
B: 1.775 vdc
E: 22.92 vdc

Q122

C: 2.530 vdc
B: 2.545 vdc
E: 22.93 vdc

When checking Q110 and Q123 can the black probe be on the amp ground?

 

[Perry Babin]

It needs to be on the source leg.

 

[seankane]

You want the voltage of all the terminals so when testing the source leg of Q110 and Q123 I will have both probes on the same leg?

 

[Perry Babin]

Just post the voltage on the first two legs. It would obviously be 0v on leg 3.

 

[seankane]

Ok thought so wanted to be sure.

Q110

G: 22.93 vdc
D: 0.000 vdc

Q123

G: 22.94 vdc
D: 0.000 vdc

 

[Perry Babin]

What's the resistance from the source leg of Q110/123 to the center leg of the negative rectifier?

 

[seankane]

Both read 000.0 ohms (NOT OL)

 

[Perry Babin]

Determine why the collector of Q122 is connected to the negative rail and the source of Q110 is connected to the negative rail (through the 0.1 ohm source resistors) but there is a 2.5v difference between them. It would appear that the 0.1 ohm resistors are open or out of tolerance.