Rockford 500BD old design

[seankane]

This amp came in with a shorted toroid, vented C59 and vented C17.

I replaced all defective parts and upon power up the cap C59 immediately vents. C17 cap did not. It is installed correctly, I double checked.

I removed C59 again and checked the pads for voltage.
+ 13.57 on pos pad
- 0.957 on neg pad

The original cap for C59 was 100uf 25v. I installed a 100uf 50v and powered the amp and it did not vent.
I checked the pads with the cap installed and am getting +46vdc on the postive lead and the same reading on the negative lead as before.
This cap is tied directly to Q13 LM317 positive regulator. The in voltage on pin 3 of the regulator is obviously also 46vdc.

D6 and D8 also have the 46vdc on the cathode end.

I am confused as to where this 46vdc is coming from. It does explain why the 25v cap was venting, but not 100% sure how its getting there.

 

[Perry Babin]

Measure the voltage directly across the two terminals of the capacitor. What do you read?

 

[seankane]

I tested for audio before reading your post and it shorted U10. I replaced U10 and it shorted again powering up. So U10 is removed and I also removed Q108, Q109, Q101, and Q102. I was going to replace them anyway.

Will this change the out come of the requested reading?

If not the reading across C59 is +22.09vdc

 

[seankane]

With the driver and said outputs removed the positive leg of C59 is only 18.50vdc now.

 

[Perry Babin]

Are 4 of the outputs still in the circuit?

Troubleshooting may be simpler if you disconnect the output from the power supply by desoldering the red/black wires on the rectifier end.

You have to measure directly across the capacitor. It's floating with the rails.

 

[seankane]

4 outputs are still in the amp. Yes I measured directly across and it was +22.09vdc

 

[Perry Babin]

That supply is floating with the output. Desoldering the rectifier ends of the red/black wires and connecting a load across the speaker terminals will make reading voltage and viewing signals simpler.

Without the rail voltage, do you have clean DC on the positive terminal of that capacitor?