Rockford T20001bd

[seankane]

Q30 has got so hot it burned the board and de-soldered itself and is completely missing. I don't have access to my schematics. Does this transistor drive the UC3526ADW? The traces are burned but it looks to connect to Vcc and Vref? Any idea what the part number is for this transistor?

 

[Perry Babin]

http://www.bcae1.com/temp/rockford - powerT20001bdSCH-4755-B.zip

 

[seankane]

What exactly is Q30's function in the circuit?

 

[Perry Babin]

I'm not exactly sure. It looks like it could provide additional current to the 5v reference by monitoring the current drawn by pin 17. That input doesn't do much more than feed the 5v regulator.

 

[seankane]

I wonder why it failed, the schematic does not give the part number. I have another here I'll look on that board.


Upon powering up the amp it squeals and wont power off until B+ or ground is unhooked.

 

[Perry Babin]

Did something connected to the vref line short?

What's the resistance from pin 18 to ground?

 

[seankane]

OL.

 

[Perry Babin]

If there was a short, it appears to be gone now. Maybe a strand of wire fell into the amp and that was the short that destroyed the transistor.

 

[seankane]

The pin had corrosion on it. After cleaning it I retested and got a different reading.


After testing it again I got .908k ohms




The resistors in the same circuit are way out of tolerance. I will replace the resistors and the transistor and post my results.

 

[seankane]

I acquired the build sheet from Rockford and Q30 is a MPSA56. Just an update for forum use.

 

[seankane]

Amplifier is fixed, I found the following problems.


Q30 burned off board and missing,
R77 out of tolerance
R78 out of tolerance
U1 defective
C16 defective
C94 defective


After replacing these components amplifier is up and running and produces rail, regulated, and clean audio. This is an update for the forum in case anyone else has this issue.