A problem in my diy Zen

[volle]

Hello I'm a new "Zendiy". I hope I will show you my realization soon...
I meet a problem maybe someone met too.
During the test of the two channels, I replaced the 50v unregulated by a power supply and the two worked very well. When I tryed with the 2x18v transformer, I have a problem on a channel I can't explain. R4 has no action on the circuit. The voltage across R0/R1 is about 0,75v and I can't adjust it. I havn't this problem on the other channel. Q4 seems to work well and I can observ all the voltage showed on the schematic (no exactly the same value due to R4).
I don't understand what could be the cause of this behavior. Moreover there are no difference between the two channel circuits.

Thanks for your help and happy new year

Vianney

[tomchaoda]

Which version of Zen are you referring to?

Thomas

[volle]

Hoops!
It's the Penultimate Zen (Part4).
Thanks.

[joensd]

Do you have about 22V at the drain of Q1?
Are you sure the pot´s ok?
Pop another one in if you have one spare or better measure it.

Cheers
Jens

[tomchaoda]

Do this one step at a time. What I will do first:

1. Make sure the 2X18V is in series, not parallel.

2. Check to see if the output after the bridge rectifier and the 25000uf cap is +50V.

Once this is certain, then you can check the rest of your main board.

Thomas

[volle]

I tested my board as you said. The pot is still ok.
I can observ about 47V after the cap (I have only 22000uf) ; and 40v at the source of Q5.
On the " good " channel, I have 26,8v at the drain of Q1 when there is 0,66v across R0 and R1.
As N.Pass said : " Adjust R0 so that the drain voltage of Q1 is 1/2 the regulated voltage plus about 2 volts ".Thus I need 22V. So I will adjust R0… as soon as possible.
On the channel wich doesn’t work , I check the drain of Q1.
Effectively there is a problem, I have 3,3v whatever R4…. I see about 4v between the gate and the source of Q2 but 0V between the gate and the source of Q1.

Thanks for your help.

Vianney

[joensd]

If you have both resistors R0&R1 installed and measure 0.75V you should have a bias of 2.3A which doesn´t sound too bad so far.
The drain of Q1 is a big problem. Of course the whole bias circuitry doesn´t work then.

My first guess would be you touched the mosfet in a kind of loaded moment and it has gone to semiconductor heaven.
Did you measure the mosfet?
It probably has a short.

You can use this article to test the mosfet or your multimeter.

If this is not the case you probably have a short in your wiring somewhere but I don´t think so.

Good luck
Cheers
Jens