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BC890XLT Discriminator Tap

 

BC890XLT Discriminator Tap

Last week I bought a used Uniden BC890XLT scanner and added a discriminator audio tap.  Here’s how I did it:
The first thing to do was open the case.  The outer sleeves come apart on the top and the bottom.  There are 2 screws on each side and one screw on the back that I removed.  I took both the top and bottom sleeves off to explore the inside, and discovered I only needed to remove the top to tap the discriminator audio.  Once inside I found the location of the discriminator audio which is pin #10 of IC #3, 3359DA.  Pin #10 is on the top right corner of the chip:

Rather than solder to the chip, I preferred to solder to the lead to the resistor at TP3 which is connected directly to PIN #10 of the IC.  I put a 10K ohm resistor in series with a 10 Î¼F tantalum capacitor. 

I wanted this modification to be removable so I didn’t drill a hole in the case. Rather, I ran a connected wire to the outside of the case through an opening in the side of the case. 


I then ran the wire in the space between the case and the outer sleeve on the side.  I then ran it around the corner to the back of the scanner.  I connected the ground wire to the chassis via the screw that holds the accessory RCA jack.  I put heat shrink tubing on the outside of the wires and connected them to a 1/8″ mono phone jack.  

Radio Shack Part Numbers:
1/4-Watt 10K ohm resistors – #271-1335
10μF Tantalum Capacitor – #272-1436
1/8″ Mono In-line Phone Jack – #274-0333
Assorted Heat Shrink Tubes – #278-1627