Rockford Fosgate 600.5

[Perry Babin]

Which FETs (circuit board designation) read shorted for 10 seconds?

Did you try powering it up when you had the sub channel outputs out of the circuit to see if the rest of the channels were in good working order?

 

[mike49504]

I cant check to see if the channels work since its drawing excessive current from the get go. I have no outputs in the amp right now just power supply fets and all of the power supply fets read shorted Also across the power and ground terminals read shorted for 10 secs then they test fine

 

[Perry Babin]

Power it up via a current limiting resistor and monitor the current draw. While it's drawing excessive current, measure the voltage across the gate-source of the power supply FETs (while watching the current draw). Does the current draw change when you have the meter on the FET?

Clamp the transistors and power it up for a few seconds at a time to prevent damaging the FETs.

 

[mike49504]

So red probe on gate leg and black probe where?

 

[Perry Babin]

Black probe on source leg and red probe on gate leg.

 

[mike49504]

The reading was 10.30 volts on all of them

I only powered it up a few secs at a time and smoked my current limiter no change in the current draw

 

[Perry Babin]

Do you read ~0 ohms between...

the collectors of the PNP driver transistors and ground?

pin 7 of the 494 and ground?

Are you sure you installed the new drivers in the correct locations (pnp/npn)?

 

[mike49504]

Pin7 to ground 0.2 ohms, collectors of pnp drivers to ground 0.2 ohms

 

[Perry Babin]

What's the DC voltage on pins 9/10 of the 494?

 

[mike49504]

Ok i pulled all the fets out of the board.

Between pads 2 and 3 for the power supply fets it reads shorted then it will start climing like im charging the caps then if i switch the probes around it reads shorted between pads to to 3 for 10 secs before it starts climbing again

 

[Perry Babin]

That's your meter charging/discharging the filter caps.

When I asked for the voltages previously, I want the voltage from 1-3 on the FETs.

 

[mike49504]

Before i blew the resistor the voltage was 0.1 volts from legs 1 to 3

 

[Perry Babin]

Did you measure the voltage on ALL FETs in the power supply?

Measure the resistance from the gate leg of one FET to all others in the same bank of FETs. Do you read 2x the gate resistor value for ALL FETs?

 

[mike49504]

From gate leg to gate leg on all the fets in the bank it doubles the resistance.
From 51 ohms to 102.3 ohms

Tl494
9:5.90 volts
10:5.92 volts

Red probe on gate leg and black on source leg of the fets: 10.04 volts

 

[Perry Babin]

Defective PNP drivers or the drivers are in the wrong locations (NPN <--> PNP).

 

[mike49504]

Ok thanks Perry,

That problem is solved.

Next problem there is no output on any of channels on the amp

 

[Perry Babin]

What was it?

 

[mike49504]

Defective pnp drivers like you said

 

[mike49504]

Ok amp powers up now and i tested the outputs to see if i have rail voltage.

On all of the outputs i have 6.92 volts on legs 1 and 3. No output from any channel

 

[Perry Babin]

Do you have plus and minus rail voltage on the rectifiers?

There are 4 rectifiers. Check all 4.