Discriminator tap mod for the
Icom PCR-100 by "SM3WEO - Michael"

The first thing you have to do is removing the cover (would you believe that!?) by
removing the four corner screws under the radio and carefully disconnecting the speaker.
Second, and quite important you have to desolder the antenna connection ground
from the pcb (Printed Circuit Board) before removing the seven screws holding it to the bottom plate.

This is just to prevent foil separation on the pcb. Now you remove the seven screws.
Three of them are located under the cover of the shielded box so you have to take the lid off.
Ok, now you should have the pcb stripped from the whole casing.
Now flip the pcb over and locate IC10 witch is the FM demodulator IC. It is marked 31136.
Reference picture: Bottom view
When looking closer at the IC you should see a foil strip coming from under
the IC and ends up in a via pad. It is connected to leg number 8 and that is the discriminator output.
Viola! Now you can solder a wire to the via pad, that's the easiest thing to do, and you
have the discriminator tap. It is a good thing to run the signal through a 0.22 uF (micro farad) bipolar capacitor before connecting
it to whatever device you like, this is just to protect the demodulator chip.

That is the whole deal!
Note the connector I made at the rear of the unit.
I simply removed the ground screw, drilled the hole out a bit and fitted a regular RCA connector used in hi-fi equipment. It is a good thing to do the drilling while the pcb is removed to avoid drilling
into the pcb. Such thing will almost certainly lead to strange behavior of the radio!  ;-)

(Please ask for permission from Micke before taking anything from this site)

Best regards
Michael - SM3WEO
"The crazy swede"

 


A Message From David Atkins
Just a quick note to say I have tried SM3WEO's discriminator tap mod on my PCR-100, and it works. Very well indeed.

I found that the via-pad is a plated-through hole, so I connected a
small capacitor through the hole from the upper side of the PCB of my
receiver. Then a length of screened cable from the capacitor to the
suggested RCA connector (there isn't enough room to fit the jack-socket
that I would have preferred). I still had to file a 2mm deep notch in
the PCB to accommodate the RCA connector securing nut.
The discriminator output gives an excellent signal. Much cleaner than
the one fitted to my PCR-1000, in fact. Well worth doing!
Regards,
-- 

G8XBZ

Many Thanks to SM3WEO for taking the time to put this together and allowing me to post it. Please note that I cannot be responsible for any damages you might cause by trying this modification. I did mine awhile ago and mine works just fine :)
Jay L. Bray