Static killed my Jaycar theremin - help fixing please!

I got a Jaycar theremin kit for Xmas, and built it with no problems. I had just plugged in the power pack and was playing with no problems. I took off my jacket and then while playing I touched the pitch antenna, felt a static discharge, and it died! I'm sooo disappointed... how do I figure out what component got fried?

Right now if I turn up the volume all the way, I hear a faint, high sound, and if I move my hand around or touch the volume plate, the pitch changes.

I've read that it's likely this fried a transistor, but which one and how do I test? There transistors are the cylindrical "D"-shaped pieces with the 3 legs right? Marked 2N5484 and BC548? 4 of them?

Can anyone lend a hand? is there a way to ground it to prevent this from happeneing again? Thank you.

-John

Hi John

Ouch, that was unlucky. Looking at the circuit diagram, I would suggest you look at Q2 which is one of the 2N's.
But really it could be anything.

Where abouts are you?

MarkT

The most likely case are the JFETs. They are the most static-sensitive parts in that theremin.

Don

I can confirm that Kees Enkelaar himself felt these problems were most likely the 2N5484 transistors. His theremins are modified Jaycar's.

It's not a bad idea to keep one or two spares on hand for any Jaycar/Kees Enkelaar theremin owner.

OK, I'll try and replace the 2N5484's - Radio Shack's site doesn't seem to have them, any other place you guys can recommend to get them from? I googled and came up with this place (http://www.mouser.com/Search/ProductDetail.aspx?qs=sGAEpiMZZMv34NK1v5E8iQzIYI4uPWKYR1QNNblZYGY%3d). The numbers look right... I'll probably get a bunch of other replacements too (BC548), just to make the order worth it.

Thanks for the help guys!

Yes, Mouser is a good supplier. Digikey is also a good place to get parts from.

Don

If you have difficulties in finding the 2N5484 you may try the european type BF245 which has matching specifications.

.. And connect a small neon bulb between the antenna and ground for both antennas.. These are the NE-2 type with no resistor fitted..
This will prevent most future ESD (Electrostatic Discharge) problems, and cost under £1..

Provided the neon is wired close to the antenna connection, and the grounding lead is as short and fat as possible (low inductance and resistance) and connected to a good grounding point (the power supply input ground for example) tuning should not be significantly changed by this modification, as these neons have low capacitance.