SE Electronics Z3300a

[micolas]

leave 6.8k

 

[Emmathom]

35,94v on polar

 

[Emmathom]

20KΩ for drain R : never seen that on a Fet...

 

[micolas]

The problem is with the audio PCB

 

[Emmathom]

1,5mA * 20KΩ = 30v I think we should have 6-8v or so... ?

 

[micolas]

20KΩ for drain R : never seen that on a Fet...

in the circuits
JFet+BJT+Transf
Rdrain=20k

 

[Emmathom]

in the circuits
JFet+BJT+Transf
Rdrain=20k

ok...

 

[Emmathom]

so we have almost tested everything... and I don't understand what's happening...

I culd redo a full volatge test on each component, before and after it ?

 

[micolas]

so we have almost tested everything... and I don't understand what's happening...

I culd redo a full volatge test on each component, before and after it ?

a broken copper trace

 

[micolas]

a broken copper trace

you must check the continuity of the traces with the multimeter and visually with a magnifying glass

 

[micolas]

so we have almost tested everything... and I don't understand what's happening...

I culd redo a full volatge test on each component, before and after it ?

or a cold, imperfect solder
try to physically move components

 

[Emmathom]

you must check the continuity of the traces with the multimeter and visually with a magnifying glass

that's just what I did : continuity with DMM is ok between all solders taht should be...

 

[micolas]

Drain resistor in this classic topology:
20k

 

[micolas]

that's just what I did : continuity with DMM is ok between all solders taht should be...

not only between solders, but between the terminals of the components and the solders

 

[micolas]

As a last resort, black magic must be resorted to!

 

[Emmathom]

I just move all components on the audio board : no false contact...

 

[micolas]

I just move all components on the audio board : no false contact...

You could redo the solders though, to be sure. Maybe some oxidation?
*
How does dc/dc measure against the good mic now?

 

[Emmathom]

tell me : c-C3 the 47uF in in serie between 4,7KΩ and R7 ? because I got the same voltage on + and -

 

[Emmathom]

You could redo the solders though, to be sure. Maybe some oxidation?
*
How does dc/dc measure against the good mic now?

I redid most of the solders at the begining of our process and cleaned the board 3 times with isoprop. alcool...

 

[Emmathom]

I just "loose" 0,3V across R5 (4,7KΩ + 50KΩ)