This small 50Watt FM Transceiver was made in the 1990 era. Most in mobile service have seen over 25 years of vibration and temperature cycling so they have a high probability of failing. The main failure mode is fractured display numbers or a blank display. This radio came with the Kenwood ‘Lollipop’ Microphone, which has had its own reliability problems.
From a small sample of 4 units that I have seen they have all failed because of this same problem. The problem was traced to the small 9 pin surface mount connector that connects the LCD Board (CN205) to the Front Panel Board (CN1). It becomes open or intermittent. This is a blind mating connection and during disassembly. I have found all of the connector pins of CN205 have pulled off the Front Panel Board. The connector should pull apart but it gets stuck together from friction or flux and when the LCD Board is removed it just pulls the female part of the connector off the board by breaking the solder joints. This connector is right in the center of the Front Panel Board
My analysis shows that the plating of the pins on the female connector is poor which caused solder dewetting and subsequent solder fracture of the leads. A few years of temperature cycling and vibration helped that along too. I suspect there are a lot of these radios out there in junk boxes.
Here is how to repair the Radio. (This also applies to the TM-441A and TM-541A).
The first step is the Front Panel disassembly which is a little tricky. Remember you are now handling ESD sensitive parts and you must employ ESD Handling guidelines. If you need training go to http://www.esda.org/onlinecourses.html.
Remove the 4 knobs by pulling them straight out, Remove the Power button and the Low/Dim button. Remove the mounting nuts on the Rotary Selector knob and the microphone connector. Then pry the Black Front Panel Bezel up and off. This requires prying up 2 tabs on the top edge and 2 on the bottom and gently pulling the bezel off. Now the LCD Board will be exposed. The other 3 push buttons are held in place by foam rubber that may be deteriorating, If it has crumbled, just hold the 3 clear buttons in place with your thumb until you can get the bezel flipped over. The LCD Board can now be gently pried off, side to side. This action is going to pull the CN2/CN205 apart and it will either pull apart successfully or it will pull the solder joints off the Front Panel board. If the connector comes apart correctly there may be only a few cracked solder joints that need to be resoldered or flux on the connector pins which need cleaning.
If the female connector (CN205) is pulled off the board then it needs to be totally cleaned, retinned and replaced on the Front Panel board. Then the connector solder pads on the Front Panel Board must be cleaned or reflowed so there is a flat surface to resolder the connector. The connector pins should be flat (coplanar). This takes a 7X microscope and a very small soldering iron. The connector leads are 0.010 in. wide, so registration is not too difficult but you must get it flat. Be careful not to damage the nearby chip capacitor. This assembly was originally reflowed in a solder machine, No one did any hand soldering here before. Make sure the solder joints are smooth and shiny and that there are no solder bridges.
Inspect the connector blades, they should all be protruding out beyond the plastic slot. If not, gently push down on them so that the contact pin is in the channel.
If you want to replace the Memory Battery while you have the unit open you have to remove the metal bezel. If it is down to 2V you probably should replace it. The battery is on the back side of the Front Panel Board. Remove 4 screws on sides, top and bottom of the metal bezel, then remove the 2 screws on the Front Panel PCBA, One on the right and one in the TO-220 case. Then pull up the Front Panel Board straight up, disconnecting the two through hole connectors.
If the connector was the cause of the failure the unit may now be repaired by this resoldering. You can check it as you reassemble the unit. This repair is a little tedious but it might save the whole radio from being junked. Unfortunately there are many other failure modes and there is no guaranty that this will fix the radio. The LCD has a 49 pin elastomer connector which can become disconnected.
If the LCD still is blank you may have to do a factory reset. Push and hold VFO/M>V and then Power the unit on. If that is unsuccessful try Push and hold MR/M key and then turn the radio on. I have fixed several radios using this repair technique.
If that is unsuccessful and the LCD screen is still blank, the radio may still be usable. You just need to know how to push the buttons in the blind. Connect the radio to a 13V, 10A power source, Reset the microprocessor (Push and hold VFO/M) , Turn radio On, Push PTT on dummy load with a power meter and frequency counter. You should see 50W at 144.000 MHz. on the TM-241, Push the Power button and reduce the power to 10W (QRP). Then push the VFO button and just dial up the frequency you want using the rotary knob and using the frequency counter to select it. Then Lock the radio, Press “F” key and then MHz/Lock.
You can inject CTCSS by Pushing “F” and holding it for 3 seconds, Push “Tone”, Rotate the dial knob 4 clicks for 100 hz, and then push “Tone”.
Then push “Tone” again and you will get the “T” (which you can’t see on the display), then push VFO and it will stay in Tone Transmit.



Now you can at least sit it in a corner and monitor your favorite frequency, like 146.52 MHz.
Sherlock W0RW
| VA7AV | 2023-03-04 | |
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| Sherlock Investigates Common Failure of a Kenwood TM-241A, FM Transceiver | ||
| This is a great article and drove me to repair my TM-241A. I think my repair makes for an interesting story... I installed the radio in my Pathfinder back around '95. It bounced around plenty of backroads for few years, then, you guessed it, the display went flakey. The Internet didn't really exist, and clearly, this post explaining how to do the repair didn't either! So I opened up the radio, as carefully as I could with the limited skills I had at that time. I thought I could try re-seating the LCD panel - that was my only idea. As it cracked open, I looked inside and could see what I thought were traces lifting. Crap. I figured I had trashed the radio completely by taking it apart, so I put it back together and it went into a box. It came out of the box a few weeks ago after I came across this article. What the heck - I'd give it another look, since I have gained some limited SMD soldering and board repair skills since the 90s! And of course, when I opened it up this time, what I recall seeing was in fact the actual problem of this connection coming loose from the board!! I hadn't CAUSED the problem, I'd SEEN the problem... a true facepalm moment. So 25 years later, with the help of the Internet, my radio is running again. Thanks very much!!! | ||
| K9FV | 2020-06-22 | |
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| Sherlock Investigates Common Failure of a Kenwood TM-241A, FM Transceiver | ||
| Good article and the type I'd like to see more of. Not only with KW stuff, but other projects. 73 de Ken H> K9FV | ||
| N2AYM | 2020-06-22 | |
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| Sherlock Investigates Common Failure of a Kenwood TM-241A, FM Transceiver | ||
| Yes - this is an outstanding article regarding this specific major flaw but there another major flaw perhaps many hams are not aware of regarding this model. The RF Power module final amp ( S-AV17) has a high failure rate especially if this model is used out of band that is highlighted on the repeater builder website. | ||
| KM2B | 2020-06-20 | |
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| Sherlock Investigates Common Failure of a Kenwood TM-241A, FM Transceiver | ||
| Thank you for an excellent article offering highly detailed information on a main failure mode of a common radio. These kinds of detailed articles and work are what make Amateur Radio great! | ||
| VK2NZA | 2020-06-20 | |
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| Sherlock Investigates Common Failure of a Kenwood TM-241A, FM Transceiver | ||
| Excellent analysis, description and repair info Paul. Your concise instructions give encouragement to those who have a failed TS mobile transceiver of the series you describe and encourage them to attempt the repair themselves elimination trashing their unit or an expensive repair bill, something most at this time need like a hole in the head. I have a TS 231A mounted in one of my 4WD vehicles and still working thankfully, however should it have a problem I will look to see if it has a similar issue to the models you describe. Thanks for a great article regards Ross. | ||