Microphone dilemma, Kenwood TM-261A

[Martinjmpr]

Probably nine years ago or more ago I got my hands on a Kenwood TM-261A mobile 2m radio. I got it cheap off of CL and the seller told me the keypad on the mike didn't work (it came with the MC-53DM mike with the numeric keypad.)

I should point out that these microphones use an RJ-45 connector (similar to a network cable.)

A few years ago I thought I'd go ahead and order a new mike, figuring that the mike was the problem. So I looked and found a "DTMF Standard KMC-32 Mobile Microphone for TM-261A TM-271A TM-461A TM-471A TK-80 TK-90 TK-980 TK-981 TKR-730 TKR-740 " on Amazon. So I ordered it, but other projects got in the way and I never actually hooked up the radio, which sat in a box for the next few years.

So just recently I've decided to get my radios working again and I plugged the "new" mike into the radio. While the PTT worked and I could use the mike as a microphone, NONE of the keys worked to do anything (besides the numeric keypad there are also keys for VFO selection, call channel, and memory up/down.)

By contrast, while the numeric keypad on my "old" MC-53 DM did not work all the other buttons did.

So now I have a dilemma: I can,

(1) Use the radio with the "old" MC-53 mike and just know I won't have the use of the numeric keypad, which would probably be fine (except I wouldn't be able to use any function that required manual entry of keypad numbers.)
(2) Try to find another "aftermarket" mike that will work (Here's a link to one on Amazon that looks exactly like the one I ordered - https://www.amazon.com/Microphone-S...words=kmc-32+microphone&qid=1603731033&sr=8-4)
(3) Try to order an actual MC-53DM mike which as near as I can tell would cost around $70.00

Option 1 is obviously the cheapest and easiest. Option 2 seems pointless - there's no reason for me to think the aftermarket mike I have now is deficient or inoperative.

And as for option 3, I should point out that I only paid $25 for this radio, so I'm not thrilled about the idea of spending almost 3x that much just on a mike. My thought is that I'd be better off putting that $70 towards a new radio (I can get a new TM-281A for about $160.)

What I'm wondering at this point is whether maybe there is nothing wrong with either microphone - maybe the problem is with the radio somehow not accepting the numeric keypad input from either mike, in which case there's no point in spending more $$ on a mike and I'd be better off just using it as-is until I get around to ordering a newer radio.

Does anyone know if this is an issue with some radios?

About the only way to know would be to find someone with a known-good radio that uses the same microphone and see if my microphones work on their radios. If they do then I will know that the microphone isn't the problem and I can make my choice from there.

Is there any other way to test the keypad function on the mike?

 

[craig333]

Be interesting to do a poll here. I rarely use the keypad or any of the other buttons on the mic.

 

[NatersXJ6]

Just making educated guesses here:

My first thought is to contact a local ham club and plug your new mic into someone else’s radio to see if it works.

If yes, then open yours up to look for a fuse or diode protecting just the digital pins of the mic?

 

[DaveInDenver]

The MC-58DM and KMC-32 (or similarly KMC-59) are not directly interchangeable and the differences are not trivial. The function assignments on pins 1 and 8 are different. These are Up and Down on the TM-261 while on newer radios pin 8 is serial keypad data and pin 1 is unused.

The TM-261 uses voltage levels to differentiate Call/VFO/Up/Down/MR/PF from pins 1 and 8 and tone dialer on the mic line for the keypad buttons. The newer radios communicate with the mic directly using a serial data stream from a pair of TC4017BF decade counters for all the functions.

As a result only the MC-58DM will work correctly with the TM-261. The TM-271, TM-281, TM-V71, TM-D710 will use the KMC-32 or KMC-59 if you want to test your new mic. All the radios will work as a mic and PTT with any mic. It's just the secondary functions that will be all different. I wouldn't immediately suspect the new mic as bad but anything's possible I guess.

Why the DTMF keys don't work on the MC-58DM is difficult to say. Could be repairable or not. It has a DTMF dialing chip (a TC35218F) which if it's failed was discontinued about 20 years ago. But it could be something simple like a cap or other discrete component in the DMTF circuit.

 

[Martinjmpr]

The MC-58DM and KMC-32 (or similarly KMC-59) are not directly interchangeable and the differences are not trivial. The function assignments on pins 1 and 8 are different. These are Up and Down on the TM-261 while on newer radios pin 8 is serial keypad data and pin 1 is unused.

The TM-261 uses voltage levels to differentiate Call/VFO/Up/Down/MR/PF from pins 1 and 8 and tone dialer on the mic line for the keypad buttons. The newer radios communicate with the mic directly using a serial data stream from a pair of TC4017BF decade counters for all the functions.

As a result only the MC-58DM will work correctly with the TM-261. The TM-271, TM-281, TM-V71, TM-D710 will use the KMC-32 or KMC-59 if you want to test your new mic. All the radios will work as a mic and PTT with any mic. It's just the secondary functions that will be all different. I wouldn't immediately suspect the new mic as bad but anything's possible I guess.

Why the DTMF keys don't work on the MC-58DM is difficult to say. Could be repairable or not. It has a DTMF dialing chip (a TC35218F) which if it's failed was discontinued about 20 years ago. But it could be something simple like a cap or other discrete component in the DMTF circuit.

Great input, Dave, I appreciate it. You moved over the Western Slope a few years ago, right? Otherwise I'd drive up to Loveland to pick your brain.

Anyway, this kind of puts me in a "do I continue to throw good money after bad" dilemma. There seems to be little point in messing with this ancient (relatively speaking) transceiver and it's not like I have a bunch of $$ invested in it.

I think my current inclination is to keep the old mike on, with no keypad capability (but everything else appears to work) and when I get tired of it, upgrade to a new radio. Making that decision easier, the local HRO has the TM-281 on sale for $139.95 (which undercuts Amazon by $30) so I'm giving a lot of thought to just getting a new radio.

Some might think $150 (by the time you figure Denver's tax) is a lot for a single-band radio when you can get a cheap Chinese dual band mobile for less, but I'm still not sold on the quality of those. And when I think about it I feel like I can do everything I need to do with a 2m vs. a dual band.