Icom: Need pinout for Icom HM-77 mic used with IC-281H

[Om_Audio]

Hi,

My IC-281H service manual shows use of all 8 pins for female side of mic. The HM-77 mic I have only has 5 wires and a 6th bare wire. Wire colors are red, blue, white, black, green, bare. Everything I have found online even listing HM-77 specifically shows pins 1-7 in use and pin 8 unused. I need a picture of the male RJ-45 from a HM-77 or the correct color/pin num so I can crimp on a new connector.

Pics here:
https://plus.google.com/photos/105266388149148864163/albums/6121375624318361841

Thanks.

Clifford
KK6QMS

 

[ShawnInPaso]

Do you have a continuity checker or volt meter?

For starters, it's safe to say that:

Pin 1 = Red wire
Pin 2 = (up/down)
Pin 3 = (audio out)
Pin 4 = (PTT)
Pin 5 = Copper shield (bare copper wire)
Pin 6 = White wire
Pin 7 = Black wire
Pin 8 = No connection

If you make the above connections then you'd be able to check to find which wires go to the three remaining pins using a volt meter. For example, putting the ground lead from the meter to ground and checking each of the three wires while pressing the PTT button to see which one shows some voltage.

Then do the same for the up/down button. Then the remaining wire will be for the audio out.

 

[Om_Audio]

Ok, thanks- will do this later and report back.
C

Do you have a continuity checker or volt meter?

For starters, it's safe to say that:

Pin 1 = Red wire
Pin 2 = (up/down)
Pin 3 = (audio out)
Pin 4 = (PTT)
Pin 5 = Copper shield (bare copper wire)
Pin 6 = White wire
Pin 7 = Black wire
Pin 8 = No connection

If you make the above connections then you'd be able to check to find which wires go to the three remaining pins using a volt meter. For example, putting the ground lead from the meter to ground and checking each of the three wires while pressing the PTT button to see which one shows some voltage.

Then do the same for the up/down button. Then the remaining wire will be for the audio out.

 

[Om_Audio]

I got the up/down buttons to work but cannot get anything else to work. Pics updated.

Up/dn only requires blue and black to operate, no red required but work either way

If I have red/blue/black I get the following results on the following:

green- 5.24V, no change on PTT
white- 5.62V, no change on PTT
bare- 5.62V, no change on PTT

C

 

[cmdrwill]

Something to consider.. some manufactures number the RJ45 pins backwards. Even Motorola.

The 'bare' wire is the shield for the microphone lead, MICE mic earth. AKA ground.

 

[Om_Audio]

Thanks. Spoke to Icom they sent me schem and manual for mic. No luck. With the bare wire connected to pin 5 that only leave 2 wires left. Neither combo of those 2 wires produce any results. Maybe I damaged the circuit.
C

Something to consider.. some manufactures number the RJ45 pins backwards. Even Motorola.

The 'bare' wire is the shield for the microphone lead, MICE mic earth. AKA ground.

 

[ShawnInPaso]

Can you fill in the blanks here with the color of wires connected to the pins so we can see which two wires are not connected?

Pin 1 = Red wire
Pin 2 = (up/down)
Pin 3 = (audio out)
Pin 4 = (PTT)
Pin 5 = Copper shield (bare copper wire)
Pin 6 = White wire
Pin 7 = Black wire
Pin 8 = No connection

 

[Om_Audio]

Hi Shawn- mic wire colors added to your list.

I have also added the mic manual and schematic provided by the very helpful support dept at Icom whom I called today.

Basically if the white wire is the mic as suggested by an experienced friend then the PTT should be the green wire. The white and green mic wires are the 2 left. The PTT goes to an IC. I checked Q2 but see only 5.63V on the 2 legs on one side and 5.19V on the lone leg whether PTT is active or not. (not a good sign I do not think)

More than one person told me this was the best audio they ever heard and is unfortunate if I broke it!

Thanks for your input-
C

Pin 1 = Red wire - (red)
Pin 2 = (up/down) (green)
Pin 3 = (audio out) (n/a)
Pin 4 = (PTT) (?)
Pin 5 = Copper shield (bare copper wire) (mic earth)
Pin 6 = White wire (mic?)
Pin 7 = Black wire (black)
Pin 8 = No connection (n/a)

 

[ShawnInPaso]

Okay Clifford, certainly a valiant effort on your part to save the mic.

I was thinking perhaps checking for the PTT wire using a continuity meter (or your VOM set to ohms), but as you clarified the green wire goes to an IC so doubtful PTT is just a closure of the mic switch alone.

I have a similar mic, the HM103, but it doesn't provide any extra clues.

Hats off to you for your persistence in sorting out the issue.

Best regards,

 

[Om_Audio]

Thanks Shawn. I ordered an HM-133 style and will disconnect pins 3 and 8 and cross fingers. If it works I will also try to analyze the signals it generates to see what the PTT button actually does. Pics updated with HM-133 pinout.
C

 

[Om_Audio]

Did not work. Back to square 1. Looking simply to buy a used HM-77 mic if I can locate one.
C