In 1985 Kenwood, a Japanese company, began to produce the TS-940S HF Transceiver and discontinued it in the 90s. I have one of these rigs that has a built in auto tuner in it (TS-940S/AT). I began to wonder last year why its Rx was weaker than the other Kenwood HF rigs or Icom. I thought I might have missed a factory recall on its Rx parts. Despite this fact, some DX operators around the world call this rig as a DX warrior.

Last October�04 OM Thomas Sukamto, YC3BDJ, from East Java Province of Java Island, sent an email to an Internet maillist called Orari-News regarding an OM from Brazil who modified his TS-940S. Nelson Ricardo, PY1NR, has repositioned the SK125 semi-conductors/transistors of his TS-940S that caused the low sensitifity of its Rx. After he fixed it he claimed that his rig�s Rx gained 10 dB or more. Bingo! I thought that this was the answer to my curiosity. PY1NR recommended voltage measurements before and after correction. He said that if you modify your own rig, its at your own risk. Well, one element of amateur radio is a experimentation. For TS-940S, PY1NR got an amazing result.

I began to open and check my TS-940SAT right away. I found that the original position of a SK125 for Q4 (the second receive mixers) and a SK125 for Q10 (IF amplifier) were exactly the same as PY1NR had before. The original position of Q4 & Q5 were facing to each other to form sort of a letter O cut in the middle or a letter D and a reverse D. The original position of 2SK125 for Q10 were facing to the same direction to form sort of double D. Then I desoldered and reversed Q4 and one of Q10. Afterward, Q4 and Q5 faced to each other, and both Q10 faced to the same direction. When I tested, the S meter pointer deflected a little bit. So, I needed to adjust VR-3 for meter pointer zero indication. Since then my TS-940SAT gained more Rx sensitivity. Thanks to PY1NR.

For those who own TS-940S or TS-940SAT and want to fix it yourself, this is what I have done. I used these tools: (1) a 15 watt grounded soldering iron that has a sharp point tip, and it is ideal for soldering integrated circuits and other small, static sensitive electronic projects; (2) a vacuum soldering bulb/suction; (3) a magnetic screw driver; (4) an IC clipper or any appropriate clipper; and (5) a small fan. It is important that you should read the TS-940S Instruction Manual over and over before you work on it. This will help your project a lot.

These are the steps that I took to fix Q10 transistor. (1) Open the bottom case (13 screws); (2) both hands hold the metal frame for several seconds to reduce static; (3) unscrew the RF unit or the circuit board #X44-1660-00 (8 small screws); (4) unplug or disconnect the TXA cable from the TXA socket; (5) unplug or disconnect the ANT cable from the ANT socket; (6) lift up the RF unit gently and stand it vertically (be careful - you do not want to twist the old wires and break it or accidentally disconnect anything else); (7) put a supporter or stopper underneath of the RF unit, so the board stays vertically; (8) turn on the small fan facing to the board; (9) begin to use the soldering iron and vacuum soldering bulb to desolder the left transistor of Q10; (10) reinstall or reverse the transistor and solder it; and (11) reinstall the IF unit, plug the TXA cable and the ANT cable.

To fix Q4 transistor, you may follow these steps: (1) unscrew the case screw supporter (2 screws) located on the metal splitter or holder between IF unit and Control unit; (2) unscrew the IF unit or circuit board #X48-1430-00 (7 screws); (3) unplug or disconnect the gray wire from its socket on the right side (1 inch away) of 8.83mHz CW filter mount; (4) lift up gently the IF unit to the left until it lays on the hooked wires; (5) desolder Q4 transistor; (6) reinstall or reverse the transistor; (7) reinstall the IF unit and plug the gray wire; and (8) finally, put back the bottom cover. When you finish, you should check the S meter. If it is necessary, adjust the S meter. Disconnect the antenna with the transceiver in receive mode. Adjust VR-3 on IF unit for meter pointer zero indication. Once it is all set, you may enjoy an additional 10 dB Rx gain or more!

In case you accidentally damage the obsolete SK125, you may contact one of these distributors to order the parts. In North America, you may order 2SK125 for US$7.31 from the East Coast Electronics, Inc. that is a Kenwood parts distributor. Their numbers are 800-645-3516 (outside New York) and 800-632-3323 (New York). Or through their website: www.kenwoodparts.com. In Europe, you may contact the Donberg Electronics, a Deutsch company, at www.donberg.ie/descript/2/2SK125.htm. They sell 2SK125 for US$7.52 (= 5.90Euro = 4.10UKP). These prices are subject to change. You may download or forward this information from http://www.qsl.net/ab2qv/ts940sat.htm.