Rockford Fosgate punch 800a2 channel repair

[chipper]

Hi I got a punch 800a2 in need of repair one of the channels was non working I removed most of the main bad parts. Hard open resistors and output fets. I ordered new irf640's and irf9640's. My question is before I install anything what are the chances it will work again without it possibly failing again? I checked all mpsa56 & mpsa06 transistors none of them checked out shorted. Also what's the value for the source resistors? Thanks guys

 

[chipper]

More pics of the board

 

[seankane]

The source resistors are 0.1 ohm 3 watt.

If you had open source resistors you likely have damage to the protection circuitry.

Check the 1a, 2a, 5d, a7 components.

Replace all the gate resistors and the resistors marked "200" or 20 ohm.

 

[Perry Babin]

I'd suggest changing the A06 and 56 drivers. If there is ANY leakage, expect the outputs to fail.

You should also jump the transistor shown in the attached image. Without that jumper, any minor problem can cause the output transistors to fail. If you jump it AND clamp all transistors to the heatsink AND use a current limiter, the outputs should survive even if there are faults that you did not catch.

 

[chipper]

Where can I find those resistors I want to start working on this amp. Should I replace all the gate resistors? And what are they suppose to read at?

 

[mikep28]

My schematic says 51 ohms on all the output gate resistors. I bought a huge assortment of resistors from mouser once. I rarely need a resistor i don't have.


Do you not have a schematic for this amp?

 

[chipper]

No schematic I need one. Also what's the size of the surface mount resistors? I will replace the gate resistors on the outputs. Are they 0805? Thanks

 

[Perry Babin]

You need to invest in a dial caliper. They're only about $15. Until then, you can use the distance between terminals for various ICs to determine the size (1206, left and 0805, right below).

The gate resistors should be 0805.

 

[chipper]

Thanks! Also do you have a source for the 0.1 resistors? I can't seem to find any. I found four of the gate resistors to open or out of tolerance.

 

[chipper]

Can I use my 6 amp power supply after I install the new parts?

 

[Perry Babin]

If the supply is limited to 6 amps, that should be OK. This only applies if you jump the transistor. If you do not, the rail caps get charged and then the biasing is switched on. If there is a fault (and that transistor isn't jumped), a fault/defect could cause 100% of the energy stored in the caps to be dumped through the output transistors. No matter the current limit at the 12v side, the outputs can fail.

 

[chipper]

Perry babin do you have a source where I can buy 10 of the source resistors 0.1 ohm?

 

[Perry Babin]

This is what I use (mouser):
71-LVR3-0.1
LVR03R1000FB12 Vishay / Dale | Mouser

 

[mikep28]

No schematic I need one. Also what's the size of the surface mount resistors? I will replace the gate resistors on the outputs. Are they 0805? Thanks

Yeah I think so on size. What's your email ?

 

[mikep28]

Amp only draws about 1 amp at idle and you can power it enough lightly to see if it plays with a small power supply. Sent email to your Hotmail on your profile.

 

[Perry Babin]

With this amp, no amount of current limiting on the 12v side will protect the outputs if there is a problem without the transistor jumped.

 

[mikep28]

With this amp, no amount of current limiting on the 12v side will protect the outputs if there is a problem without the transistor jumped.

Oh yeah. That's happened to me more than a few times