[PPRAANet] Yaesu microphone locking experiment

[Douglas Hagerman]

I successfully modified the microphone on my FT-7800. Here's how.


The goal is to modify the lock switch on the Yaesu MH-48 microphone so that it locks all of the microphone buttons.

(Note: this has nothing to do with the LOCK function of the radio, which you select using the menu system. It is entirely within the microphone using the existing switches and circuits.)

This method uses a documented feature of the microphone circuitry shown in the schematic diagram. The diagram is somewhat cryptic, but basically there are five small pads on the circuit board inside the microphone that can be open circuits or short circuits, depending on whether there is a tiny blob of solder connecting the two halves of the pad. Each pad is about 1/8" in diameter, with a slot in the middle, and you either connect the pad's circuit by putting a blob of solder on the pad to short the two halves together, or disconnect the pad's circuit by removing the blob.

When I say "blob," that actually means "neat but small bit of solder carefully and properly melted into place using conventional soldering technique."

The five pads are numbered on the schematic, but not on the board. They are in a pattern on the board like this:

  O
O
  O
O
  O

and numbered like this:

  5
4
  3
2
  1

On the schematic, the numbers are JP5001 through JP5005. This is shown on the wiring diagram and also on the small chart that shows lock switch options. It is confusing because on the chart, an O means "short" and an X means "open," which seems backwards.

The FT-7800 comes with an MH-48 A6J microphone. I don't know what the A6J indicates. This microphone comes stock with pads 3 and 5 shorted, which causes the lock switch to disable the UP, DOWN, ACC (which is labeled P3), D/MR (labeled P4), P1, and P2 buttons. In the stock configuration, the DMTF keypad buttons and the PTT switch are still live when the lock switch is in the lock position. You can confirm that your microphone is configured this way by looking carefully at the pads and comparing their configuration to the chart.

The chart shows that the lock mode can be changed to ALL by shorting pads 2 and 4 and leaving 1, 3, and 5 open. In that configuration, all of the microphone buttons and keys are disabled when the lock switch is in the lock position. (The key illumination still works regardless of the position of the lock switch.)

To do this, you need to get out your solder wick and remove the blobs from pads 3 and 5, and then soldering blobs onto pads 2 and 4. It is fairly delicate work because things are small. The white glue that secures the nearby wires will melt if you touch it with the iron. Don't drop the PTT button when you take the three screws out of the back of the microphone. Reassemble and test.

It works for me, and now I don't have to worry (as much) about accidentally sitting on the microphone.

W0UHU Doug.




> 
> After bouncing around in a car all day yesterday in constant fear of accidentally keying my microphone, I decided to poke around on the Internet to see if there was a modification that would allow me to lock it completely. This is on a Yaesu FT-7800, which comes with an MH-48 handheld microphone. The mic has DMTF buttons plus a few others that have various functions, plus the big PTT switch that is so easy to sit on. Also it has a switch that turns on the key illumination, and a lock switch that only locks the keys--but not the PTT switch.
> 
> I found this schematic, http://homepage.ntlworld.com/rg4wpw/mh48a6j.pdf which seems to show that there are jumpers inside the mic that change the function of the lock switch. The table on the lower right shows various jumper configurations, including one that apparently locks all of the mic functions, including the PTT switch.
> 
> Has anybody played with this feature? Just curious about what sort of trouble I'm about to get into?  :-)
> 
> Thanks.
> 
> W0UHU Doug.
>