B2 tests to verify it’s safe to install VFETS?

Unfortunately the procedure in the manual requires the V-FET's to be installed for the adjustments.

Yes you can but it's somewhat dangerous.
you can adjust DC offset without the v-fets installed, right ?
What is the Vint Age method to take care of that feedback to make sure the Bias adjustment is also functioning properly, before you bring in the v-fets?
 
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ha ha, get the pop-corn and the soda

index.php


I hope that it is clear for you

Hi Patrice, Quick question:
based on your curves you shared earlier....how can you tell that any of the v-fets were good or bad??

The test on the Peak Atlas tracer test is done at 5v and less than 4ma. That is no where near the operating conditions of these v-fets in the B-2 and no where near their rated parameters in the Yamaha datasheet, right?

So, in theory, all could be testing good on the peak atlass but cold have a breakdown voltage of let's say, 15v?? as such, none would be suitable for duty in a B-2, but would pass the multi-meter test and the peak atlass test with flying colors.
I know that is a far stretched assumption, but the point is that if we go away from the multi-meter test, there are different tests available.
I also use the peak meter and I find it fantastic, but it is limited to low power devices. Even for Jfets with high IDSS is not really well suited for as it taps out at 12mA, and so if I need to match those, I need to rely on different methods.

Now, if someone could marry the brute strenght of one of the real curver tracers such as the Tex 577, 576, with the nice software solution of the Peak Atlas meter, then we would have one very powerful tool available (if anyone is aware of the Tex 576 software solution already available, that is a step in the right direction but nowhere as polished as the peak atlass software)
 
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Hi Peter

based on your curves you shared earlier....how can you tell that any of the v-fets were good or bad ?? compare and you will see bad V FET curves non found bad with ohm meter method

The test on the Peak Atlas tracer test is done at 5v and less than 4ma. That is no where near the operating conditions of these v-fets in the B-2 and no where near their rated parameters in the Yamaha datasheet, right?

yes ! of course but a detected bad V-FET with PEAK ATLAS will stay bad

In my point of view , I don't need to buy TEKTRO curves tracer because the cost will never be refund by repairs before 35 years ....I will not be here in 35years

AK members ask recommendations for repair on B2 . They are free to follow them or not . I share what I think it is reasonnable to share . All risky procedures will not be given here .

I have perfectly refixed 6 B1 (have two ready to be finished at least ! ) and 8 B2 (have one in pieces ready to be shipped back to his overseas owner ) and my PEAK ATLAS is really fine enougth !

I have bought one B3 in original condition . My PEAK ATLAS will be perfect to work on it ( once the customer's amplifiers will be gone ! )

Each unit I switch ON is working perfectly
 
I don't need to buy TEKTRO curves tracer because the cost will never be refund by repairs before 35 years ....I will not be here in 35years
Hi Patrice, I was gonna mention that the Tex tracers are more rare, hence cost more in EU, because they (the Tex tracers) prefer to hang out here on the West Coast. We have better weather :D

upload_2019-3-1_13-47-29.png
 
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Ok here's an update.

I opened up my working B2.1, [made sure the caps were drained, pulled out the VFETs in a very organized manner <--that's for you Pete] and took measurements between the Red and White wires. Both sides measured almost exactly at 124v without the VFETs just like the other B2 (B2.2).

So, unless someone sees an open man hole cover in my path, I think I am ready to put B2.2 back together and test her. Of course I assume all risks of doing so.
 
Ok here's an update.

I opened up my working B2.1, [made sure the caps were drained, pulled out the VFETs in a very organized manner <--that's for you Pete] and took measurements between the Red and White wires. Both sides measured almost exactly at 124v without the VFETs just like the other B2 (B2.2).

So, unless someone sees an open man hole cover in my path, I think I am ready to put B2.2 back together and test her. Of course I assume all risks of doing so.
I did not see an answer as to what work you did to the driver boards of the B-2.2??

let me elaborate:
if all you did is a recap of the unit, and all you replaced on the driver boards were the bi-polar lytics (one for each board), then I would spot check some voltages around the driver stage and move forward....at your own risk of course....

If you replaced other components, hence have a higher risk of things to go wrong, I would not connect those v-fets yet.
 
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From my notes I replaced the following on the Driver Circuit Boards in B2.2:
C114
L-VR101
R-VR101
L-VR102
R-VR102
D101
D102
D110
D111
 
From my notes I replaced the following on the Driver Circuit Boards in B2.2:
C114
L-VR101
R-VR101
L-VR102
R-VR102
D101
D102
D110
D111


well, that is the added risk I was reffering to....anything wrong with those replaced diodes and there is your open man-hole without cover, right in front of you.
be prepared someone here might grill you for replacing those diodes :) :whip:you just have to take it Henry:rolleyes:

OK, If I were you I would consider the following:
  • cross-check and verrify those replaced diodes
  • I would not put in the v-fets back in untill I'd verify the voltage test points on the driver boards
  • then I would reach out to one of the seasoned techs here (in private) and they might be able to help further (for very good and obvious reasons, they would not do that in an open forum)

CAUTION! I am aware that you are aware of this but here it goes:
Without the v-fets attached, the main filter caps will take forever to drain, hence you must be particularly cautious about draining the main filter cans before you bring those v-fets back in....yeah, I know you mentioned you are aware you need to drain 'em, but I just wanted to hear myself saying it
 
Sorry but for obvious reasons I'd rather not be the one posting dangerous procedures ...

I fully understand the reluctance to post in a public forum risky testing procedures that do pose a danger because they must be performed on an open and energized amplifier. But if you or anyone else would be willing to send me a private message with this information it would be appreciated.
 
But if you or anyone else would be willing to send me a private message with this information it would be appreciated.

The problem is not in posting how to do it , but you don't have the knowledge to do it , that the problem and risk to destroy your V FET
If any one was able to repair a B2 (or B1, or any other V FET Amp ) everybody knows that this is not so easy
Sharing info , OK
Sharing experience this is not possible
Anyone can not claim to be a qualified technician
 
But if you or anyone else would be willing to send me a private message with this information it would be appreciated.

The problem is not in posting how to do it , but you don't have the knowledge to do it , that the problem and risk to destroy your V FET
If any one was able to repair a B2 (or B1, or any other V FET Amp ) everybody knows that this is not so easy
Sharing info , OK
Sharing experience this is not possible
Anyone can not claim to be a qualified technician

Going back to my first post, what I am looking for specifically is guidance on what tests can be performed without the VFETs installed in order to determine if it is safe or not to reinstall the VFETs. I am not asking for advice on making any repairs in this thread. Am I being overly simplistic and there is something more complex here I am not aware of?
 
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No , nothing strange or magic , here .
Just a unit not made to work without V-FET in place
What I am trying to make you understand is that you have none confirmation of the shape of your V-FET . I explained you that a test with ohm meter is OK to determinate if your transistor is shorted or not . A curve tracer will answer to all of your questions . An ohm meter will not tell you that curves are bad like in my previous post (almost flat) .
You want to take the risk to place inside the unit a set of "unknow" V-FET . Do what you want to do, but every aware member gave you good advice and I will follow them if I was you .
 
So here's an update on what I did and the final results. First I had some conversations outside of this forum with someone who explained to me in detail the steps necessary and associated risks of testing a B2 without the VFETs installed. The phrase "Fools rush in where angels fear to tread" came to mind. And since my Momma didn't raise no fool I decided not to tread there. Instead, I carefully reviewed and double checked everything I had done to the amp and compared all parts I had installed to my other working and refurbished B2 amp to make sure all parts were installed correctly. I even pulling a number of transistors to verify them.

I installed the VFETs. Powered her up (gulp) and performed all the adjustments as required with no issues. She has been in my main listening system playing gloriously for the past two days.
 
So here's an update on what I did and the final results. First I had some conversations outside of this forum with someone who explained to me in detail the steps necessary and associated risks of testing a B2 without the VFETs installed. The phrase "Fools rush in where angels fear to tread" came to mind. And since my Momma didn't raise no fool I decided not to tread there. Instead, I carefully reviewed and double checked everything I had done to the amp and compared all parts I had installed to my other working and refurbished B2 amp to make sure all parts were installed correctly. I even pulling a number of transistors to verify them.

I installed the VFETs. Powered her up (gulp) and performed all the adjustments as required with no issues. She has been in my main listening system playing gloriously for the past two days.

Your mama certainly raised no fool...or someone that gets discouraged easily.
Congrats Henry!

Now, for your third B-2, we need to get you a real curve tracer... One of these:

upload_2018-12-28_14-16-33.png

:D
 
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So here's an update on what I did and the final results. First I had some conversations outside of this forum with someone who explained to me in detail the steps necessary and associated risks of testing a B2 without the VFETs installed. The phrase "Fools rush in where angels fear to tread" came to mind. And since my Momma didn't raise no fool I decided not to tread there. Instead, I carefully reviewed and double checked everything I had done to the amp and compared all parts I had installed to my other working and refurbished B2 amp to make sure all parts were installed correctly. I even pulling a number of transistors to verify them.

I installed the VFETs. Powered her up (gulp) and performed all the adjustments as required with no issues. She has been in my main listening system playing gloriously for the past two days.

Congratulations! If you know what you are doing, this will work most of the time.

On my last B2 rebuild I tried this approach. I quickly pulled the plug when I saw smoke. Luckily, it was only a resistor smoking and the VFETs were fine. It was a long and tedious diagnostic procedure finding the problem after that with VFETs removed.

And after that experience I quickly bought that PEAK curve tracer...
 
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