Rockford Power 550X 4 Channel

[seankane]

Hello all. I have a Rockford Power 550X I am working on with a small issue.

The board number is PC-3094-E.

When it came in it had no audio. I replaced the RCA jacks and D2 and D3.

The amp powers up fine and idles fine, no current draw or anything unusual.

All channels bias fine and produce clean audio.

However....The right rear negative bridging terminal has -1.836 vdc on it.

The only time I notice a problem is running it bridged. At low or no volume it is very staticy. Once the volume is increased it sounds totally fine.

I am kinda stumped here as in where to look for a problem.

Anybody have any ideas?

 

[Perry Babin]

Do you have the same voltage on the two bases of the differential amplifier transistors?

 

[seankane]

As in Qx105 and Qx106?

 

[Perry Babin]

Qx01 and Qx02.

 

[seankane]

All the bases read the same: 0.047 vdc except Q301 and Q302.

Q301 reads -1.285 vdc

Q302 when tested showed about 0.533 vdc but made the amp draw 20 amps on my supply and screech.

 

[seankane]

Hey Perry did you get a chance to read my last post?

 

[Perry Babin]

What is the DC voltage measured directly across the following resistors. I would ask for them in smaller groups but I haven't had much time to visit the forum.

R317-R323 and R326.

 

[seankane]

R317: 0.039 vdc
R318: 0.040 vdc
R319: 4.82 vdc
R320: -0.361 vdc
R321: 0.378 vdc
R322: -1.152 vdc
R323: -0.534 vdc

R326: 0.525 vdc

 

[Perry Babin]

I don't see anything there that's unexpected.

With the black probe on the negative speaker terminal, what's the DC voltage on the 4 terminals of C312 and C314?

 

[seankane]

Hello Perry its been awhile since I posted on this not sure if you remember where we were at.

Black probe on negative speaker terminal and red probe on

C312: 0.946 vdc
C312: 2.574 vdc

C314: 1.248 vdc
C314: 3.145 vdc

Let me know what you think.

 

[seankane]

Did you get a chance to read my last post with the values I posted Perry?

 

[Perry Babin]

I didn't see it earlier.

You can't use the negative speaker terminal. Use the amplifier's ground terminal or one of the non-bridging speaker terminals for the reference (black probe).

 

[seankane]

Ok I will re-check. In post number 9 you requested that I use the negative speaker terminal for testing, you must have meant the non bridging terminal.

 

[seankane]

C312: 0.656
C312: -0.986

C314: -1.004
C314: 0.654

 

[Perry Babin]

You'll need to connect the RCA shield ground to the primary ground.

The next time you post the voltages, make a note of which terminal of the capacitors to the 3.32k resistors.

 

[seankane]

So I can un a jumper from the rca shield to the amps main ground terminal?

 

[Perry Babin]

Yes.

 

[seankane]

The negative terminal of C314 which goes to the 3.32k resistor
reads: -0.998 vdc

The positive terminal of C314 reads: 0.654 vdc

The negative terminal of C312 which goes to the 3.32k resitor
reads: -0.998 vdc

The positive terminal of C312 reads: 0.648 vdc

 

[Perry Babin]

What's the resistance between the base of Q301 and the base of Q302?

 

[seankane]

Resistance between base of Q301 and Q302 reads: 46.0 k ohms

Also as a side note I have -1.898 vdc on the drains of Q310 and Q311.

Could they be leaky?