MH-48A6J Mic Problem

[KB3NRY]

Hey all,

I have an FT-1802M. Recently (within the past month), I noticed that when I key up my mic (MH-48A6J), the DTMF-1 tone is pressed/sent as if the 1 key is stuck down. I couldn't see anything from the outside that looked like the 1 key was stuck. Today, I took the mic apart and cleaned it out. I pulled the rubber keys out and cleaned them and everything. Everything looks good inside and not like anything is being pressed unncecessarily; however, I have the same problem after re-assembling it.

Has anyone else had this or a similar problem? Any ideas what could be wrong if the key isn't physically stuck?

Thanks in advance.

[5B4AJB]

Take it apart again and check the PCB matrix (with a magnifying glass & good light) for shorts & cracks, it could also be the button is misaligned.

If that looks good, check the components on the board for shorts/dust etc - blast it with a can of air, or brush it all down with an old toothbrush.

[edit] you could try cleaning under the silicone of the offending key, lift it gently and use a cotton bud soaked in foamclene, alchohol, lighter fluid etc, clean the contact underneath that too (on the PCB).

[KB3NRY]

Thanks for your suggestions, Demetrius.

Sadly, I think, I have a worse problem. Before I did the thorough inspection that you suggested, I decided to try a friends mic. It turns out his mic did the same thing. So not it appears to be a problem with the radio. I believe these radio have a complete reset button for software issues. Short of that, I'm not sure where to begin on this solid state radio.

Any suggestions, anyone?

[5B4AJB]

You'll probably have to rewire the mic - if it IS compatiable with the radio.

Check in the manual, if that mic is listed under the available options.

Lots of radios put a 5V signal on one of the mic pins - it's always advisable to double check the wiring before plugging anything in...

[KB3NRY]

Both of our radios take the exact same mic. Nothing should need re-wiring. His mic works on my radio, but it is producing the same problem as my mic, which leads me to believe its a radio problem.

[AE6ZW]

MH 48A6J determine which keys are pressed based on what resistance value are connected from each of 2 pins to gnd. PIN #1 SW1 ( GRN ) , PIN#2 SW2 ( GRY ) . except PTT has its own line. the radio read voltage level with ADC PIN #1, and PIN#2 determine which keys are pressed. so if plugging any MIC will work as if [ 1 ] key is pressed , most likely radio is not reading voltage correctly. for your reference you might want to take look at schematic of your radio and schematic of mic, I believe all of Yaesu radio come with schematic ( which is great , only Yaesu do that ) , and you can find schematic of mic by searching on internet. PIN #1 SW1 ( GRN ) , PIN#2 SW2 ( GRY ) should go to ADC of CPU , I have FT-2800M, which use same mic, in that schematic, both SW1, SW2 pin go right into CPU for voltage reading, each PIN also have 100 k pull up resister to 5V,
P.S. you might want to check voltage level of SW1, SW2 with known good radio, vs yours, if it is quite different, you might want to check those 2 100k pull up resister, make sure if these are good.

[KB3NRY]

Wow, this post is a little old. Thanks for the help everyone. I'm sorry to take your time with solutions. I vaguely remember having this problem, but I'm pretty sure I just turned on the Yaesu Wires feature by accident.

[AE6ZW]

I am glad you got it working, I like Yaesu radio, and working on radio is my half of hobby as talking. 73 NIKO