DIY U87 CIRCUIT PROBLEM

[Uncle-G]

Hello fellow DIYers,

I've got a home-assembled U87 mic that I had working until this morning. I had both circuit boards wrapped with plastic wrapped and aluminum foil on top - all housed in 3D printed tube (plastic). I had
problems with hum here and there and I decided to add another layer or aluminum foil around the existing on and in the middle of wrapping the circuit boards around I heard a loud click (sounded like one I unplugged the phantom power) and the mic went silent (the mic was live in my headphones). I have tried different preamps and systems with no avail. I have examined the circuit board and there is nothing that I can see that is wrong. I obviously shortened something... anyone has any ideas? Would shortening kill a capacitor or something else?

 

[Khron]

Most likely the JFET. Replace that and see if it comes back to life.

 

[Uncle-G]

Thank you Khron, I'll give this a try. I also found that one side of Cinemag transformer reads 33 ohm and the other one overloads. Does this sound alarming?

 

[RuudNL]

Both windings of the transformer should at least measure a resistance!

 

[Uncle-G]

Khron, you were right! It was the dead JFET! I replaced it with another one (I got three with my initial material order).

RuudNL, that is right. But the transformer seem to work (my measurement skills suck, maybe?).

Thank you very much for your responses, gentlemen, and have a good day/night.