Hi atmosphere, just a little box with 3 cables which tells about the characteristics of a part. No, I didn't do anything like special on and off. Might there be a chance for being still alive?
Yes, big chance. VFET shows short between D and S without gate voltage applied. Transistor testers I have cannot correctly identify them, as they cannot provide negative voltage big enough to turn them off.
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Ok, sounds good. Was pretty desparate and down yesterday. Does it mean, I just have to put it back in the circuit and start amp? This is what I did, but it didn't work. Any recommendation?
After bolting the Fets to their position, I forgot to solder them to the PCB :-( So of course no function! Since Nelson mentioned, V-Fets shouldn't see vgs before vds to get not destroyed I was pretty scared when I found there was no function even after soldering. I was not able to get them to work even when tried to raise vgs. Then I took it out and did the function test. The rest as described above.
Cheers Ernst
So, how to proceed? Doing the process as on the other channel shows nothing. What does switching on or off mean in this case?
Do I only need a negative enough vgs within the amp? Do I need a small circuit which applies gate lets say 18V vds and a negative vgs prior to that?
I am a bit scared.
Cheers Ernst
Hi Ernst,
Perhaps you can try testing the part using something like the setups here:
http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-21.html#post4392065
http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-26.html#post4394173
You'd want the Vgs to start close to -18V and slowly bring it up while you
measure for voltage drop across the 1 ohm resistor.
If your Vfet came from the essential kit the marking will tell you the
Vgs to expect for 0.5A current.
Hopefully your Vfet is still fine.
Cheers,
Dennis
Perhaps you can try testing the part using something like the setups here:
http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-21.html#post4392065
http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-26.html#post4394173
You'd want the Vgs to start close to -18V and slowly bring it up while you
measure for voltage drop across the 1 ohm resistor.
If your Vfet came from the essential kit the marking will tell you the
Vgs to expect for 0.5A current.
Hopefully your Vfet is still fine.
Cheers,
Dennis
This is a depletion mode device. That means is on (shorted) until it gets enough negative bias to turn it off.
Usually a transistor tester mode of a DVM is enough voltage to turn it off, but in this case that is not so although you can measure a change if the gate is still good. You put the red lead on the Source and the black lead on the Gate. If you then measure the source to drain resistance, you will see that the resistance has increased a little bit; obviously you need two DVMs to do this.
Hi Atmasphere, when I apply the voltage from the diode test part of the DVM to gate and source the resitance between source and drain increases and goes back again when I release the diode test DVM.
Does this mean, the Fet is still alive? Probably
So I have to switch it with the ciruit that Dennis proposed. Huh, I had a bad end of the day yesterday evening, but it is getting better
now. Thanks for you help guys - athmasphere, metallicus, Dennis and Nelson for help and good words. I'll let you know after next weekend. No time until then.
Cheers
Sounds like its fine.Hi Atmasphere, when I apply the voltage from the diode test part of the DVM to gate and source the resitance between source and drain increases and goes back again when I release the diode test DVM.
Does this mean, the Fet is still alive? Probably
Huh, I had a bad end of the day yesterday evening, but it is getting better
Thanks for you help guys - athmasphere, metallicus, Dennis and Nelson for help and good words. I'll let you know after next weekend. No time until then.
Cheers
Fet still Alive!
Yes it is! Definitely. I took my heart and my Curve Tracer out of the box. I never tried, as I read somewhere that one has to apply Vgs before Vds. And I didn't know if Locky's Curve tracer would act like that. But thanks to Dennis link provided above I have seen a plot from a member and so I did as well. E voila: Here it is: Thanks again. Being absolutely happy.
Yes it is! Definitely. I took my heart and my Curve Tracer out of the box. I never tried, as I read somewhere that one has to apply Vgs before Vds. And I didn't know if Locky's Curve tracer would act like that. But thanks to Dennis link provided above I have seen a plot from a member and so I did as well. E voila: Here it is: Thanks again. Being absolutely happy.
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Sorry for the wait, I didn't see your question until now.
See post #2731 http://www.diyaudio.com/forums/pass-labs/276711-sony-vfet-amplifier-part-2-a-55.html#post4987426 for answers.
Member, Scandinavian, L-shaped profile....hmm. That would be me!
And I know, it is really hard to find old posts in a long thread.
You need some?
It is definitely available.