What's to say ?
Papa slapped me with a textbook some years ago.
I can't go around hitting gurus, which leaves me no choice but to slap others.
http://www.diyaudio.com/forums/pass-labs/43204-pass-monster-3.html#post504972
Papa slapped me with a textbook some years ago.
I can't go around hitting gurus, which leaves me no choice but to slap others.
http://www.diyaudio.com/forums/pass-labs/43204-pass-monster-3.html#post504972
Work finished early today
Good, at least you now know the oscillation can be stopped.
Because the Pumpkin is balanced in and out, it therefor has two feedback paths, only one half needs to play up to cause problems on both sides.
What you need to do next is to turn it into an unbalanced pre - easily done.
With the inputs grounded and no links on R1 & R3, fit a shorting link across R7 (obviously with the power off) this will bias off Q7, the feedback will be via R5 only, power up and check J4, there should be no output unless there is something wrong with Q7, if there is - don't proceed with the next bit; check that Q2 gate is at 0V, if not - fit a link across R4; check for oscillation at J3.
Remove the links on R7 R4, repeat the above procedure with R8 R2 J4.
Don't feel too
You will get there in the end
Finally something that makes sense.
I have replaced the gate resistors with the 221R and removed the caps at the inputs.
Now, with R7 shorted I get a peculiar waveform at J4 - sort of a mixture of highish amplitude low MHz and superimposed on it low amplitude HF (20MHz).
All the matched transistors were supplied by ZenMod but no care was taken with packaging. I suppose they might have succumned to static in flight from Greece.
R14 being OPEN circuit has been ruled out by replacing it temporarily with 470R. I'll measure it though as the 221 is back in circuit.
R14 is indeed GOOD
I did measure all the resistors as they were being inserted as I'm not over confident with the 4 band colouring scheme.
Incidentally I was able to measure R14 in circuit so that tends to indicate that the gate junction of Q7 has not failed.
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That's going to be a real pain, chopping PCB tracks - not sure I/m happy with that just yet.
Got me ready to burst into tears.
The neighbors 15 miles east of you would say : na freili, kene Spur !
I've viewed both Pumpkins under the microscope. One was appaulling. I found many shorts. The second one though looks OK.
I still feel that the poor ESD precautions might be the cause.
Oh no I did not mean this kind of movie you like to go to......
again a problem of my English..... "moves" in the sense of many guys here help to solve the problem.....
The neighbors 15 miles east of you would say : na freili, kene Spur !
hm, hm .......? Is it English?
everybody was sending me FETs in the last years using plastic bags....
I had never a failure....
I wasn't expecting that, after re-reading my suggestion, I missed out an important bit - fitting a shorting link across the gate & source of Q8 to turn off the constant current sink, could you re-do the experiment with this included.
My apologies for my omission.
Ok, repeat the experiment with a link across R8 and the gate/source of Q6 to check out the other half of the circuit.
With R8 shorted and Q6 shorted (the shorts have been removed from the other half).
There is oscillation at J3 and J4.
Q1 gate is at approx -9V.
To me this could indicate that Q6 is short circuit.
This might be a "Red Herring" but with R7 shorted and Q8 bypassed, the LED string is not illuminated.
With R8 shorted and Q6 bypassed the LEDs are illuminated.
There is oscillation at J3 and J4.
Q1 gate is at approx -9V.
To me this could indicate that Q6 is short circuit.
This might be a "Red Herring" but with R7 shorted and Q8 bypassed, the LED string is not illuminated.
With R8 shorted and Q6 bypassed the LEDs are illuminated.
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