Rockford Fosgate punch power 250.2

[chipper]

Got this amp in today in the mail my first 'punch power' fosgate. Anyway I need help with getting it repaired. I noticed a burned spot and a missing 4700 50wv cap. The burned spot looks like burned trace? Any help would be appreciated! Thanks

 

[chipper]

Here's an additional pic also do they still sell those capacitors?

 

[chipper]

Heres the burned area.

 

[Perry Babin]

Clean the burned area to see what the actual damage is.

I have a schematic marked 767-j but it shows 4 crossover cards. Email me if you want it.
babin_perry@yahoo.com

The same series caps may not be available. You can use something like the Panasonic TSHA series.

 

[chipper]

Also amp won't power up. I checked all six MTP50N's none are shorted neither are any of the channels. I cleaned the burned area I'll post up another pic. Any ideas what should I check as to why amp isnt powering up? Or could it be that there's a missing capacitor?

 

[Perry Babin]

It's not likely to be the capacitor. The other capacitor will do the job at idle (and likely at full power).

If you have 12v on pins 8, 11 and 12 of the 494, post the DC voltage on all pins of the LM339 and the 494.

 

[chipper]

When checking those do I put negative probe on ground terminal?

 

[chipper]

Ok I have 11.55v on 8, 11, and 12 on LM494

Voltages for LM339

Pin 1 12.95mv
Pin 2 109.1mv
Pin 3 11.53v
Pin 4 126.4mv
Pin 5 2.340v
Pin 6 4.50v
Pin 7 0.450v

TL494C

Pin 1 126.1mV
Pin 2 4.51v
Pin 3 009.7mV
Pin 4 04.85v
Pin 5 1.420v
Pin 6 3.250v
Pin 7 125.4 mV
Pin 8 11.50v

Pin 9 120.1mV
Pin 10 127.2mV
Pin 11 11.50v
Pin 12 11.52v
Pin 13 4.90v
Pin 14 4.90v
Pin 15 4.89v
Pin 16 127.5mV

Let me know if I checked right?

 

[Perry Babin]

8-14 on the 339?

 

[chipper]

Here's what I got for LM339

Pin 8 - 111.4mV
Pin 14 - 002.1mV

And how does this happen? None of the power supply fets shorted all tested fine I removed them from the board. Also get no gate voltage on all 6 pads most is 126.7mV.

 

[Perry Babin]

8 to 14 not just 8 and 14.

 

[chipper]

Ok for LM339

Pin 1 - 156.4mV
Pin 2 - 155.7mV
Pin 3 - 12.25V
Pin 4 - 127.4mV
Pin 5 - 2.370V
Pin 6 - 4.51V
Pin 7 - 121.4mV
Pin 8 - 002.3mV
Pin 9 - 4.51V
Pin 10 - 4.51V
Pin 11 - 018.5mV
Pin 12 - 122.4mV
Pin 13 - 008.4mV
Pin 14 - 008.5mV

 

[Perry Babin]

In the future, use something other than a hyphen as a separator. It's not a big problem here but it it can cause problems if any of the voltages are negative.

Check R19 to confirm that it's within tolerance.

 

[chipper]

R19 - 39.21k ohm

 

[Perry Babin]

It's supposed to be 412 ohms.

 

[chipper]

I changed R19 with a new one. I had 2.67 volts on the gate pads. I put in two fets and applied power real quick amp turned on but D5 went up in smoke.

 

[Perry Babin]

Remove D5. Does the amp power up?

 

[chipper]

D6 also reads shorted and not sure about D3 also has a low reading

 

[Perry Babin]

D6 being shorted could have caused D5 to fail. Unplug the RCAs and re-check D3.

 

[chipper]

I read 0.300 on D3 both ways when I test it. Is that normal for that one? I know most will be between 445 or 500