DR1200T.7

     3. Locate the solder tabs for the display lamp near the volume control, 
        there is a VIA about 3/8 inch from the bottom tab.
     4. Solder a 6 inch wire into this VIA so it exits on the side of the PWA 
        opposite the display. Run the other end to the new switch.
     5. Now for the tricky part! This trace runs from this VIA under the 
        volume control to a connector marked CN202, pin 12. It's near the 
        power on/off switch and LED. Cut this trace with the xacto knife, 
        anywhere from this VIA and pin 12. The point I picked was 
        approximately 3/8 inch from the VIA right below the edge of the
        metal housing for the display, right before it goes under the volume 
        control. Watch out for the trace just below it.
     6. Connect another wire from the other side of the switch to the bottom 
        side of the connector CN202 pin 12.
     7. Test for a clean break of the trace (do not add the display to the 
        PWA yet) by connecting the radio to a supply and turn on, lights 
        should go out when the button is pressed. If the switch does not 
        control them inspect for a clean cut. 
     8. Checking the display contacts. Reinstall the display (do not screw 
        to the chassis yet) and power up the radio again. Rotate the 
        frequency knob to insure all the display segments work. If there is 
        a problem, try bending the tabs so they apply more force on the 
        rubber connector. Last resort is to remove the display again, and
        stretch the rubber connector once more.
     9. Now you are home free! Install the switch, notch the case and 
        reassemble.
 
     After performing this delicate operation, and reviewing the lamp specs. 
     a simpler alternative to the switch would be to use 18V lamps. Here are 
     two equations that predict lamp life and intensity VS operating voltage: 
     Life multiplier = rated volt divided by applied volts to the 12th power. 
     Intensity = applied volt divided by rated volts to the 3.5 power. From 
     this equation 18v will give 20x life at a 41 percent reduction in 
     intensity. 12.5v operation with 14v lamps = 3x life increase, but 
     reduces the transmitter power 10 percent. I operated the 14V lamps at 
     11V to simulate 18V lamps at 13.5v and found the intensity satisfactory. 
     The P/N for 18V lamps is Chicago Miniature CM 7220 or JKL 7220. They 
     should be available from a local electronic distributors or mail order 
     distributors such as Allied in Fort Worth 1-800-433-5700 or Newark in 
     Chicago 1-312-784-5100. I doubt it if radio shack will stock them. 
 
     We hope the above information will help you.  Address any comments or
     suggestions to me, Jim, KD6QVO.