Hi Salas
Last week I built and tested left channel and was rejoycing about it´s sound and absence of hum.
Yesterday I finished right channel, installed it and it works but the left one stoped.
I read -35mv in the output
Between R10 (4,7k) and Q2 I read only 0.3v instead of 7,9v I have on the working channel.
What can be wrong ?
Ricardo
Last week I built and tested left channel and was rejoycing about it´s sound and absence of hum.
Yesterday I finished right channel, installed it and it works but the left one stoped.
I read -35mv in the output
Between R10 (4,7k) and Q2 I read only 0.3v instead of 7,9v I have on the working channel.
What can be wrong ?
Ricardo
Do you have power from its individual reg? Can you have lost some led or jfet ccs on its 1st stage local Vbias?
I have power 28v and the voltages in the first stage are ok.
The problem seems related with the riaa 2nd stage.
I have 26v on top of Q5 (output buffer) where I read 14v on the working channel
I have 0.3v on top of Q2 where I should have 7,9v
measuring R5 (without power on) I get 1M on the working riaa and 45k on the dead one. (I desoldered R5 and it measures 1M but in place it measures 45k)
Can there be a fault in C4 ?
Ricardo
The problem seems related with the riaa 2nd stage.
I have 26v on top of Q5 (output buffer) where I read 14v on the working channel
I have 0.3v on top of Q2 where I should have 7,9v
measuring R5 (without power on) I get 1M on the working riaa and 45k on the dead one. (I desoldered R5 and it measures 1M but in place it measures 45k)
Can there be a fault in C4 ?
Ricardo
In the simulator it gives me 0.31V on top of Q2 if C4 is faulty and does not block DC. Measure, and if you can find DCV on Q2's gate, then your C4 is bad, passing DC.
after shut down, r6 reads 34r so it´s ok but r5 reads 35k instead of 1m.
I believe I must build a new board 🙁
I believe I must build a new board 🙁
I'm not up to date with all that you tried. But I think it's the transistors. If you haven't checked them, you should. For jfet just make sure with a 9V battery that you got the proper Idss, that's how I test them. For npn, it's enough to check with the diode tester between B-E and B-C pins, one way street 😀
I don't think a board that worked all of a sudden turns bad.
I don't think a board that worked all of a sudden turns bad.
What lacquer? Don't do that again. Scratch around second stage parts before dissasembly. When it played ok, had lacquer?
P.S. Look for what Iko says too.
P.S. Look for what Iko says too.
yes... the strange part is that it played perfectly before I installed the second channel (right).
Now the new channel works with the lacquer... and the other one has strange behaviour in second stage..... I am wondering about the board because lifting one leg of R5 and using the dmm I get 1M. If I touch the board with the lifted leg, the reading goes down to 900 and if I insert it on the hole (without soldering) the reading goes to 400.
Now the new channel works with the lacquer... and the other one has strange behaviour in second stage..... I am wondering about the board because lifting one leg of R5 and using the dmm I get 1M. If I touch the board with the lifted leg, the reading goes down to 900 and if I insert it on the hole (without soldering) the reading goes to 400.
What happens if you power each board from the same shunt, one at a time? Another thing that can happen because of the lacquer is bad connections when you replace parts. You can check if the lacquer is conductive on the megaohm setting of the dmm.