Phoenix Gold XS4600 blown trace

[Perry Babin]

Measure the gate to source resistance for the PS FETs again.

Were your resistance values ohms or k-ohms?

 

[jrodajames]

Q7-Q8-Q9 are in ohms

Q10-Q11-Q9 are m-ohms

 

[jrodajames]

On Q7-Q8-Q9, I get the same reading both way g-s and s-g

On Q10-Q11-Q12, I only get a reading from s-g. From g-s I get ol

 

[Perry Babin]

Is that with the drivers out of the circuit?

 

[jrodajames]

In circuit on the board

 

[jrodajames]

Would bad fets cause the fuse to blow when the amplifier is off. The fuse blows as soon as power is connected, thats what led me to believe it was the blown trace.

 

[Perry Babin]

Q8 at 2.2 ohms was definitely bad. The readings for the 2 banks of FETs should read the same. That's why I suspected the drivers. Did you check the drivers for leakage and open junctions?

I'd pull the drivers again and recheck the gate to source resistance. You should also pull the FETs to check them out of the board to confirm that they're not shorted or leaking from the gate to either of the other terminals.

 

[jrodajames]

All the PS fets other than Q8 are good

Q7, S-G=OL, G-S=OL, S-D=4.09m-ohm

Q8, S-G=2.8, G-S=2.8, S-D=2.8

Q9, S-G=OL, G-S=OL, S-D=4.04m-ohm

Q10, S-G=OL, G-S=OL, S-D=4.08m-ohm

Q11, S-G=OL, G-S=OL, S-D=4.05m-ohm

Q12, S-G=OL, G-S=OL, S-D=4.04m-ohm

 

[Perry Babin]

With those and the drivers out of the circuit, what do you read g-s on the pads on the board?

Did you check the drivers for leakage and open junctions?

 

[jrodajames]

I did check the drivers for open gates and leakage, all test good

The g-s on thee board for the ps pads reads ol on all, q7-q12

 

[Perry Babin]

How are the values different when the only difference is the drivers being in the circuit?

 

[jrodajames]

I believe I am misunderstanding you, did you want me to check the open pads on the board ?

Or the g-s on the ps fets both in circuit and out to compare?

 

[jrodajames]

Also Perry I hope you know how much I appreciate your help.

 

[Perry Babin]

Yes, open pads.

You checked the non-Q8 FETs and all read open. Something was causing the G-S to read different for the two banks when you had the FETs (minus Q8) in the circuit,. I'm looking for whatever is causing the differences.

 

[jrodajames]

 

[jrodajames]

 

[Perry Babin]

That's OK.

What changed from the values on post #16?

 

[jrodajames]

Those readings were in circuit, I can resolder and recheck.

Should I leave the driver's q2,q3,q4,q5 out of circuit?

 

[Perry Babin]

Do whatever you need to do to repeat those readings so we can try to find what's causing the difference between the banks (if there actually is one).

 

[jrodajames]

Okay everything is back in circuit

Q7, g-s 6.3 ohm, s-g 6.3

Q8, g-s 2.8, s-g 2.9

Q9, g-s 6.3, s-g 6.3

Q10, g-s 39.1 m-ohm, s-g 9.3 m-ohm

Q11, g-s 39.08 m-ohm, s-g 9.3 m-ohm

Q12, g-s 37.18 m-ohm, s-g 9.3 m-ohm