Rockford BD1501

[Dr Zeus]

I've got this amp on the bench which powers but does not play. I get 161v rail across the twisted black/red wires.

Reading the DVD, I checked out U11 with my oscope and all waveforms look pretty good.

I did find a cracked cap; C27 next to U14 which I replaced with a new piece.

Input pin 1 of the MIC4420s which I can measure reach-wise are graphing a ~-9vDC flat-line. According to the DVD the input should be a +-3v square off -9v but this line on mine is just flat and straight, like the amp is in protection.

This amp being a BD1501 has several different dominations from the BD1500 I was looking at on the DVD, and thus I scratch my head a bit on figuring it out.

[Perry Babin]

Is there any DC across the speaker terminals?

Does the triangle waveform on pin 11 of U11 swing ±5v?

Is the amp in protect mode?

If there's no protect LED, what's the DC voltage on pins 1 and 7 of U21?

[Dr Zeus]

Hey Thanks Perry, I was just about to post my findings on U21 - Pin 6 has -6.5vDC on it, and according to the DVD it likely means bad. I'm in the process of replacing it out.

Pin 1 has -8v, Pin 7 has +8v

No DC on terminals.
Pin 11 of U11 is good
Red LED is on for protect

[Dr Zeus]

U21 I believe did the trick. Any way to make the repair more robust? This is the second BD amp I've found with a failed U21.

[Perry Babin]

They fail randomly. Some seem to last forever and I've had some that only lasted a month.

I don't know if it's the circuit that's the problem. I've seen quite a few of the TL072 become leaky to the negative supply, even when used for ordinary audio circuits.