Rockford fosgate punch 45 no output

[chipper]

I have here my very first punch 45 mosfet amplifier. It won't play anything just bits of static with some music hardly. I have to turn up my source to actually hear anything but it's just big loud partial static with very little music. One channel had a shorted output labled "TP3055A" it's by motorola. Anyone have an idea what's causing the other channel not to play right? I checked the driver transistors and some resistors. Thanks guys

 

[Perry Babin]

Which revision?

If you're not sure, post a photo.

 

[chipper]

Okay give me a sec.

 

[chipper]

here ya go

 

[Perry Babin]

Do you have both positive and negative 15v on the power supply pins of all 3 op-amps?

 

[chipper]

How do you measure it? Is it the side with the line/circle?

 

[Perry Babin]

Pins 4 and 8 (see image below). Check all 3 op-amps.

 

[chipper]

Meanwhile I look for my meter again..... Are there any subs for the MTP3055A?

 

[Perry Babin]

I'd use an IRF540.

 

[chipper]

I assume MTP12P05 = IRF9540?

 

[Perry Babin]

Close enough for this amp.

 

[chipper]

Do put the probes on those pins? (4 - 8), if so it had a reading of 40 vDC?? And on pin 8 - 3 I had a reading of 14.75 this is for LM833N the one nearest the LED.

For TL072CP I got a reading of 40 vDC from pins 8 - 4. Like I said I'm not sure if I'm doing it correct still learning.

 

[Perry Babin]

Black probe on the ground terminal/wire of the amp.

 

[chipper]

May I ask you a question? Is the power supply non regulated? Because when I got the voltage to at least 14 volts the rail voltage atomaticly went from 37 vDC to 50 volts. How does this little amp work?

 

[Perry Babin]

This amp cannot produce ±50v with 14v.

It's unregulated.

 

[chipper]

Okay back with results TLO72CP from pin 8 it has 29.95 vDC and same as LM833N (near led) the other LM833N has 14.12 vDC from pin 8 with the probe on the negative wire. Does this mean the op-amps need replacing?

 

[Perry Babin]

What do you read on pin 4 of those op-amps?

 

[chipper]

TL072CP = 0.570v
LM833N = 0.557v
LM833N = 13.17v

 

[Perry Babin]

Is the last one positive or negative 13v?

Is there a burned trace where you see the exposed copper on the board in the attached image?

 

[chipper]

Yes it's a positive 13. And yes it looks like there was something there that exploded because there's like pieces of wire sticking out like if there was a component there.