View Full Version : Kenwood TM-241A
10-05-2005, 02:24 PM
I just bought a previously owned TM-241A and discovered while attempting to program frequencies into the memory, that when pressing the "F" key to initiate the memory save feature, the entire control panel face power, and apparently the audio power drops out for a fraction of a second as if there's a bad transistor in the power circuit. This also occurs when attempting to transmit with a 2-meter whip attached. Has anyone experienced this problem, and if so what was the corrective action?
10-06-2005, 02:07 PM
I have a couple of 241s and a 261.
first i would do a complete reset. power on with some button pushed, i didnt look up which.
Also I would take the covers off and check all internal cable plugging, and eyeball for loose or broken wires,cables. also check screws that hold down the big black output module in back.
Check everything mechanical. board mounting screws etc.
If you really need to get deep into it. Remove the front panel, display etc and check the board for cracks. My used 261 had ,had the tuning knob whacked andit seperated the encoder parts. replacement 12 bucks.
I changed the back up battery on my 241(used) in about a half hour, which should indicate how long to complete disassemble the front panel and re do..
After all that you may have to start with test equipment.
one step at a time. there is no majic wand.
10-07-2005, 12:09 PM
Thanks for the suggestions. I had already done the reset and checked the obvious weak points for damaged boards, etc. The behavior is something like an overheating power regulator or transistor. I just thought someone might have done this repair on this rig before.
10-14-2005, 04:09 PM
This problem seems to be common among TM-241A's. I just got another rig with the identical symptoms. When I transmit into a known good 2 meter whip, the power and display cycle off and on in a regular period of approximately once every quarter second.
10-22-2005, 02:38 PM
Does anyone have experience with this TM-241A problem?
Sounds like pulses from the radio's CPU interrupt line (INT4?). #Look very carefully at the control board. You could also have RF getting into the control board / CPU lines.
Kenwood had a service bulletin (April 1990 SB-966) for a similar problem that caused memory loss in the TM-231 model.
ASB0966A.JPG #& ASB0966B.JPG are on the Kenwood web site ["B" has a schematic and control board layout for the TM-231]
ASB-0966 TM-231A Intermittent Memory Loss
ALSO, for ALL Kenwood owners, be aware of the June 2005 announcement (ASN-0002) by Kenwood of models for which repair and service is now DISCONTINUED (approximately mid-1980s or earlier mfg.)
10-23-2005, 12:55 AM
I had some intermit problems with my 241, ended up being the tone board, which was just double side taped to one of the shield casings, had worked it's way off the tape and was grounding out the board.
10-23-2005, 01:02 AM
Thanks to both of you for your suggestions. I've had the case off a few times and will take another look inside. It would be nice if the problem was as simple as a wayward tone board, but I suspect something deeper in the power circuit. Everything is worth trying however. I'll let you know if it gets resolved.
10-23-2005, 01:25 AM
The tx problem you've describe reminds me of the first time I powered up my TM-231 (1989). The TM-231 and probably the TM-241 need a power supply voltage of greater than approx. 11 Volts. Make sure you have a power supply that can supply enough current. I was and am still disappointed that the TM-231 draws so much current even with the power knocked down to low. The front panel blanking out and cycling back on sure sounds like the p/s is dropping low during TX. The 11 Volt low limit is, I believe and have not verified, to be due to the drop out of a 3 terminal regulator (problably the 8V regulator). The 8V regulator needs about 11 volts to operate properly or, in other words, there needs to be > than 3 volts across the regulator from the input terminal to the regulated output terminal. At one time I thought of replacing the 8V regulator with a low-drop-out type. These can continue to operate with only a volt or less overhead. This problem, with other poor features, have upset me enough that I have never purchased a Kenwood rig ever since. False output power meter indication, 5 uV for S9 (should be 50uV!), poor RF brick reliablity(SV-17?), lack of a CTCSS decoder built-in, intermittent memory loss (mentioned in previous comment), poor solder joints on the front panel( CTCSS tones were intermittent), letters/numbers wore off mic in a very short time, cracked smt cap due to main pcb incorrectly installed, temperature sensitive hybrid IC (455kHz IF board), poor out of band rx sensitivity, etc, etc.. (Sorry...it upsets me because this was one of the most expensive rigs I purchased up until '89) 73, Pete
10-23-2005, 01:33 AM
Thanks for the wealth of information. I will look into all of your points of suggestion. I'm fairly convinced that my power source is large enough. I have another TM-241A that functions properly with the same supply. I agree that solder joints and workmanship on the inside of this rig leave a lot to be desired! Nevertheless, I'll check that 8v regulator, perhaps it's the culprit.