SK-401 "SOFT KEY" INSTALLATION INSTRUCTIONS PART S SUPPLIED WITH T HIS KIT : (1) SK-401 "S oft Key" Circuit Board Assembly (2) 6-32 x ¼" Round Head Screws (1) Nylon Threaded Spacer (1) #6 Internal Tooth Lock Washer To start the installation, read these instructions very carefully. Now unplug the amplifier and remove any input, output and control cables that may be connected to the back of the amplifier. Place the amplifier upside down with the rear panel facing you and rem ove 6 screws and the bottom cover. You are now ready to proceed with the installation. () The exact mounting location of the SK-401 is not too critical. Be sure to keep the RED and BLACK leads as short as possible. The most convenient place I have found is just behind (or next to, dep end ing on your version of the L-4B RF deck) the 24 volt supply terminal strip on the right side near the ON-OFF rocker switch. Try to align the unit such that the BLUE wire is nearest the wiring harness and the flat part of the large HEXFET transistor is facing the front of the RF deck. Once you have decided on a location, mark a location where the large hole in the SK-401 is. This is where the mounting spacer attaches to the SK-401 and also the location of the hole for the mounting screw. Very carefully drill a hole that will clear a 6-32 screw at the point you just marked (#27 drill). Do not use too m uch pressure because you w ant the drill to stop after just penetrating the chassis. Clean up any burrs from the hole. Place the #6 lock w asher onto one of the 6-32 x ¼ " screws and place the screw through the hole you just drilled. Screw the threaded nylon spacer from the SK-401 kit onto the screw and tighten well without stripping the threads in the spacer. Mount the SK-401 circuit board onto the nylon spacer using the other 6-32 x ¼" screw. Position the board as previously described. Unsolder the WHITE & BLUE wire from the antenna relay jack on the back panel. Remove the diode that is between the a nte nna relay jack and a small 1-lug terminal strip next to the jack. You can discard the diode. The lug should not have anything connected to it after you removed the diode Route the BLUE and YELLOW wires from the SK-401 along (or in) the wiring harness so that both w ires end up near the antenna relay jack. Solder the YELLOW w ire and the WHITE & BLUE wire (unsoldered from the antenna jack earlier) to the terminal of the 1-lug terminal strip next to the antenna jack. This effectively connects these w ires together. Solder the BLUE wire from the SK-401 to the antenna relay jack. This wire will be attached where the WHITE & BLUE wire w as unsoldered from earlier. () () () () () () () () 1 () Solder the RED wire from the SK-401 to the +24VDC lug of the te rminal strip near where you mounted the SK-401. This lug has the positive (+) end of an electrolytic capacitor, the cathode (banded) end of a diode and a 2.2K res istor soldered to it. Solder the BLACK wire from the SK-401 to a convenient chassis ground. The terminal strip described above USUALLY has 1 or 2 ground lug s ava ilable for this. O ne or m ore lugs are directly connected to ground as they are used for mounting the large terminal strip. Replace the bottom cover and any cabling. () () This com pletes the installation of the SK-401 "Soft Key" module. You may not SEE any difference in the operation of your exciter or amplifier, but you will know that you have reduce d the stress on the exciter's keying relay or transistor. SK-401 "SOFT KEY" MODULE PARTS LIST R1 & R2 R3 C1 & C2 D1 D2 Q1 Q2 22K ¼ W 5% 10K ¼W 5% 0.1µF 50VDC CERAMIC 1N4005 (1A 600 PIV) 1N60 GERMANIUM MPS2222 IRF610 HEXFET (N-CHANNEL) HARBACH ELECTRONICS Jeff Weinberg ­ W8CQ 468 County Road 620 Polk, OH 44866-9711 (419) 945-2359 http://www.harbachelectronics.com info@harbachelectronics.com 2 ...