How to enable my Graupner JR X412 radio ?

[Roel]

The guy who sold me the radio said it was very popular,
but why can't i see it then here on the forum...

Should i follow the instructions for other JR radio's ??

[Roel]

I opened the transmitter.
it contains two seperated circuit boards.

There are 3 wires going from the processor-board to the HF-board : black-yellow-red.

Can i just build the last circuit of the manual (for serial port), assume black is ground,
en try out yellow or red??

Or will i blow up my radio then ???

[Mike Roberts]

Roel

You have it! Yes use the serial IRQ circuit. Look at the circuits on my website. Try the standard one first. If this does not work go to the JR version. My circuits use a 10k input impedance so chances of doing damage is very very small.

Black is most likely ground (check with multimeter to battery negative) and yellow signal.

Let us know how you get on so others can benefit from your experience.

Mike

[Roel]

It works

I used the JR circuit on www.customelectronics.co.uk

Due to availability of some old resistors i used some different values then the ones on the website :

- For the transistors i used the common BC548 and BC558.
- The 22k 's became 18k 's
- And the 470k became 390k

In the radio there is one wirebundle (black-yellow-red) going from the lower circuitboard, to the circuitboard with the crystal and antenna. The black wire is the ground and the yellow wire is the signal wire to use (red is power, but you don't need it).

When you open the radio and look on the crystal-circuitboard, you can see that they 'forgot' a component at the lower left (2 times 3 holes not used). I guess this will will be used for the buddy connection in more expensive versions of the transmitter. But you can now
use these holes for the FMS-interface : Use a left hole (=ground) and a center hole (=signal), from the first or second row, doesn't matter which, they are connected on the bottom...


Good luck to all other X412 users...