ICOM IC2400A Mic problem

[W2NJS]

In the manual for any Icom transceiver there is a pinout diagram for the microphone connections. That diagram will tell you if a pin is connected, or active, and what it does exactly. It's a lot easier to work on a mic connection problem is you have the diagram in front of you.

The HM14 mics were a relatively low-quality item, and I've had to rebuild several of them over the years. I have one now being used with an old 3200 dualband radio and it has a black back and a gray front because it was made up from two old units. The unit now on eBay for a BIN of $50 has no warranty and I'd stay away from it unless there was a return privilege if the thing didn't work properly. These mics appear regularly on that board.

And to clarify one other point that was mentioned in the previous posts, the keypad on these units is used to transmit DTMF tones only and not to enter a frequency. The up/down switches on top of the mic are used to step the frequency up or down with the step size having been selected previously in the setup menu.

 

[ramal121]

There are eight pins on the connector but two are not needed. Pin 8 is receive audio and pin 4 is a voltage indicating the squelch is broken. Neither of these two serve a purpose in a microphone. That is why 8 has no wire but surprised 4 does. The six others are needed to run a DTMF mic.

Strange that the wire to PTT GND pin 6 is missing. Regardless, there still needs to be a ground connected to the common terminal of the switch. The other ground is pin 7 MIC GND and I wonder if the HM-14 is wired different to use this single ground. If you short pins 5 and 7 on the radio you should still see it go into transmit. Go back and ohm out the switch via pins 5 and 7 and see if there is any connection.

By what you're saying I'm thinking the mic has been modded or "repaired" by someone at a point in time.

 

[topgun1986]

Ok..

Finally resoldered the loose cables back onto the respective pins of the plug.
Then performed continuity tests on all the cables, from the plug to the microphone where they terminate.
Continuity tests fine on all cables.
Plug in and hit transmit...nothing.
Back to the drawing board I guess.

Ramal121...
I shorted together pins # 5 & # 7 on the radio and the "TX" does light up, just like shorting together pins # 5 & # 6 made it do earlier. What exactly does that mean?

 

[k3cfc]

Ok..

Finally resoldered the loose cables back onto the respective pins of the plug.
Then performed continuity tests on all the cables, from the plug to the microphone where they terminate.
Continuity tests fine on all cables.
Plug in and hit transmit...nothing.
Back to the drawing board I guess.

Ramal121...
I shorted together pins # 5 & # 7 on the radio and the "TX" does light up, just like shorting together pins # 5 & # 6 made it do earlier. What exactly does that mean?

It means you should see if there is continuity between the pins on the switch when it is pushed. if not there is your problem. it is just like a light switch it is either on or off!!!

 

[topgun1986]

OK...
With ohm meter inserted into pins # 5 & # 7 in the mic plug, I push the PTT switch in the microphone and nothing, no continuity.

BUT...
With mic plugged into the transceiver (and microphone taken apart), I short together pins # 5 & # 7 in the microphone (where they terminate onto the circuit board) and by golly the "TX" lights up on the radio!!!


SO...
I believe that pretty much narrows it down to the tiny, black PTT switch within the microphone, correct;
even though the (3) pins on the PTT switch have continuity between each other?

AND...
why would do the DTMF keys and the FREQ UP/DWN keys on the mic not work, if it is in fact the PTT switch in the mic that is bad??

 

[topgun1986]

PTT switch has (3) pins...

1st and 2nd pin have continuity between each other once PTT switch is pushed so the PTT switch can't be the problem.
To further credit this conclusion, even where the 1st and 2nd pin wires (from the PTT switch) terminate onto the circuit board, I get continuity when the PTT switch is pushed.

SO...
Mystery #1...
back to this brown wire on the circuit board that was never hooked to anything when I initially pulled the mic apart.

Mystery #2...
the ICOM manual that came with this rig shows a different microphone connector diagram than the one that was posted earlier by someone. This mic is wired per the diagram posted, not by the ICOM manual I have, pertaining to pin # 4.

Anyone know where I could possibly find a wiring diagram of the microphone circuit board itself? Perhaps then I could figure out where this mystery brown wire goes to, if anywere. If someone has already posted a link, I apologize in advance.

 

[ramal121]

OK, you're doing good here. I can't believe Icom has this mic wired different to where it cannot be ported from one rig to another.

To recap, the radio has a pin in the mic connector (pin 5) for PTT. To make the radio transmit, this pin needs to be grounded. You have proven this works by shorting pin 5 to either pin 6 or or pin 7 both which are grounds at the connector on the radio.

In my HM-12 mic, pin 5 PTT goes to the switch and then back to ground on pin 6. You state there is no wire to pin 6 at the mic connector. Without the wire there is no path back to ground and obviously the radio will not transmit.

I propose you hinky the mic a little to make this work. Since you confirmed shorting pin 5 to pin 7 in the radio connector produces transmit, lets move the ground path on the switch from a non existent pin 6 over to pin 7 which has to be there.

On my mic pin 7 mic ground is the braid wire in the cord. As it comes out of the cord it is just bare wire. Icom twists this braid around and slips a clear insulating tube over it. You can confirm the wire by continuity back to pin seven.

Sounds like you have the terminals on the PTT switch identified, but to clarify, of the three pins two are closer together and one is farther away. The pin that is away from the other two is the ground pin. What I want you to do is jumper (solder or whatever) a wire from the ground terminal of the switch to the braid wire that goes back to pin 7. This will provide a ground to the switch that is not there with the missing wire to pin 6. Sabe?

Hopefully that works.

 

[topgun1986]

Yes I understand.

Good news...I soldered the connections like you proposed.

Bad news...now the red wire (from the microphone speaker to the mic circuit board) has come off its solder joint and I have no idea where it was soldered to.

 

[k3cfc]

Yes I understand.

Good news...I soldered the connections like you proposed.

Bad news...now the red wire (from the microphone speaker to the mic circuit board) has come off its solder joint and I have no idea where it was soldered to.

Look very close use a bright light and a magnifying glass if necessary and see if you can find a solder pod that looks like it had a wire soldered to it. it may have a wire or two sticking out of it. you should take a pic of your projects before you start so you can refer back to it.

Good luck

K3CFC

 

[ramal121]

Well bummer. Yes you'll need to look real close to see if you can see a solder with a pointed top and maybe stranded wires inside the point. Magnifying glass is OK, but a camera lens or the unscrewed end from some binoculars will make a stand in loupe and get in real close.

Be careful though, the red wire is the power to the DTMF encoder and you don't want to stick it in the wrong spot and smoke something.

Should have checked earlier but the light bulb just went on. Does this help?

 

[topgun1986]

Thanks! That HM14 diagram is a God send!

Got mic speaker cables soldered back onto the mic board this morning.
(Fingers crossed they hold.)
Then soldered a jumper from the middle pin on the mic PTT switch to the bare copper wire (pin# 7) on the mic board.
With mic apart, I plugged mic into the radio, carefully pushed the PTT switch and it worked!!
I turned on my scanner just to make sure I could hear myself on the air, which I could!
But the DTMF keys & FREQ UP/DWN keys still do not work.
Do I necessarily need these keys to operate the radio properly?

 

[topgun1986]

Just about to give up on this mic.

Finally got it capable of TX and now my mic does not work. Both the red wire and the white wire (w/ a bare wire wrapped around it), came out of their holes on the circuit board.

The 3 wires were too short to reuse, so I soldered 3 new wires from the mic speaker to what I assume are the correct holes they were in on the circuit board. All the diagrams I have do not show the exact location of the mic speaker wires on the circuit board so I am by no means 100% sure it is correct.

Put it all back together with the 3 new wires, plugged into my radio, keyed up the mic, but was told by another ham all he could hear was my carrier. No speech.

As mentioned in previous posts, a replacement mic is about the only option I see I have now. Perhaps not the exact model but something that could perhaps work in its place; even if I had to "tweek" it a little.

Any ideas would be appreciated.

 

[k3cfc]

Just about to give up on this mic.

Finally got it capable of TX and now my mic does not work. Both the red wire and the white wire (w/ a bare wire wrapped around it), came out of their holes on the circuit board.

The 3 wires were too short to reuse, so I soldered 3 new wires from the mic speaker to what I assume are the correct holes they were in on the circuit board. All the diagrams I have do not show the exact location of the mic speaker wires on the circuit board so I am by no means 100% sure it is correct.

Put it all back together with the 3 new wires, plugged into my radio, keyed up the mic, but was told by another ham all he could hear was my carrier. No speech.

As mentioned in previous posts, a replacement mic is about the only option I see I have now. Perhaps not the exact model but something that could perhaps work in its place; even if I had to "tweek" it a little.

Any ideas would be appreciated.

I gave you this ebay number a while ago 230880413085 the listing has ended now but i don't think it sold.you can still put this number in ebay and when you get to the listing you could send him an email to see if you can buy this mic. by the looks of it your not going to fix this so i would look into this because these mics are not popular. now i am going to get coffee.

 

[topgun1986]

Found a HM14 replacement mic today and ordered. Hopefully it works fine. Will post if it does or not. Thanks again to everyone for your help! 73.

 

[majoco]

You shorted pins 5 to 6 on the rig microphone connector and the rig went to "TX".

Now you say there is no wire connected at the microphone plug socket 6.

Is the microphone compatible with your rig? May not be the original microphone.