Sony vFET pt2 N channel help

[Antealta]

Hi

Need som help.

My left channel stopped working, no smoke or burned parts.
It’s not drawing any power, I am getting unloade voltage between + and gnd, on the output stage.
Power supply is working properly, it’s a SLB power supply.

Andreas

 

[Ben Mah]

Post pictures please.

What is the voltage across R1?

What is the voltage across Z1? Does the voltage change when P1 is adjusted?

What is the voltage between mosfet drain and ground? What happens to the voltage when adjust P1?

 

[Antealta]

Over R1 bad side 1.7mV. On good side 1.3V

Over Z1 bad side 0V. On good side 7.7V. Turning the P1 on bad side, nothing happens. Good side it gets adjusted.

Voltage between mosfet drain and ground on bad side ≈ 0V, turning P1 nothing happens. Good side 11V and rising (Cold amp)

Andreas

 

[Ben Mah]

Pictures?

What is the voltage between VFET drain (case) and ground?

 

[Antealta]

Between VFET and ground bad side 41V (unloade)
Good side 35.8V

 

[Ben Mah]

What is the voltage between each side of R7 to ground?

What is the voltage between each side of R8 to ground? Adjusting P1, does the voltage change?

Voltages should be present and adjusting P1 should result in changing voltage. If no voltages I would suspect bad solder joints on the board.

 

[Antealta]

R7 bad side 41.1V and 19V

R7 good side 35.2V and 16.8V

R8 bad side ≈ 0V

R8 good side 8.1V it changes when turning P1

Andreas

 

[Ben Mah]

Either bad pot or bad solder joints at pot.

No voltage to the VFET gate is not good for the VFET - hope the VFET is okay.

 

[Antealta]

Ok

Thanks for your help 😀

This forum is great

Andreas

 

[Ben Mah]

Did you find the problem?

 

[Antealta]

Not yet, have been night time over her 😀, will take out the pot to day, and check it

Re solder or order new, or is it possible to use a 10k pot there?

The amp has been going strong for about 3 years now.

Andreas

 

[Antealta]

de solder the pot and tested it, and it’s just fine, solder it back, still no power drawn form the left side

Andreas

 

[Zen Mod]

check every resistor

 

[Antealta]

Ok

Thanks

Andreas

 

[Antealta]

All resistors is fine

Andreas

 

[Zen Mod]

change opto

if that doesn't help, time to remove mosfet and check

 

[Antealta]

Ok
Have been thinking about that one
Thanks

Andreas

 

[Antealta]

Will this work ?

Andreas

 

[Zen Mod]

if needed, Iq can be fine tuned with one resistor

so, go for it, you'll know more after change

 

[Antealta]

Ok

Thanks