MFJ-297 Desk mic

KD4OVM · #1 11-08-2009, 12:26 AM

Needing the color code for the MFJ-297 Desk Mic for wiring up
an 8 pin round mic plug for the Icom IC-740

Thanks

KI6ZIF · #2 11-08-2009, 01:15 AM

IF the mic still has MFJ's plug on it... This is the MFJ adapter part # MFJ-5397I

KD4OVM · #3 11-08-2009, 01:33 AM

Plug missing.

WB2WIK · #4 11-08-2009, 01:48 AM

Quote:

Originally Posted by KD4OVM

Plug missing.

Hmmm. It comes with a plug, wonder what happened to it?

The IC-740 did not have a built-in mike preamp, that was remote and in the microphone and powered by voltage coming from the rig's mike jack. You have to isolate that to use a different microphone...you knew that, right?

KD4OVM · #5 11-08-2009, 02:08 AM

Yes. What I need is the red wire is to ???
White wire is to ???
Black???....ect

That info. on the mic. The radio is simple.

Thanks

WB2WIK · #6 11-08-2009, 02:27 AM

Quote:

Originally Posted by KD4OVM

Yes. What I need is the red wire is to ???
White wire is to ???
Black???....ect

That info. on the mic. The radio is simple.

Thanks

Assume you've already looked at this: http://mfjenterprises.com/man/pdf/MFJ-297.pdf which does not divulge the information you're looking for.

If it were mine, I'd do some simple circuit tracing (just using an Ohmmeter) from the end of the wire back into the base of the microphone to see what each wire actually connects to. MFJ probably won't tell you, inless they're feeling in a nice mood.

KC8VWM · #7 11-08-2009, 02:29 AM

Icom IC-740 8 pin mic wiring / pin function as follows:

Pin # 7 = GND (Shield)

Pin # 1 = Mic Audio

Pin # 5 & #6 = PTT circuit. TX ON/OFF

Note: The PTT circuit on the Icom 740 (pins 5 & 6) utilizes an isolated PTT switching circuit that does not use the ground braided shield as part of the TX function.

It appears the reason the TX function is configured in this way has to do with how the VOX circuit works. The VOX probobly operates without the need of pushing the PTT button down when VOX is activated on the radio.

Seems the MFJ 297 has a "switch selector" which accomodates Icom rigs. You need to set this selector to position "A"

This is not a typical microphone and I am beginning to understand exactly why you may need help configuring it.

Caution:

One needs to exercise extreme caution wiring this microphone because the microphone has two output connectors which at a glance might suggest to someone you can connect this microphone to two seperate trancievers at the same time but DONT DO IT! The manual states this will damage BOTH trancievers!

The mic output socket you are concerned with wiring is socket "A".

The wiring from the Icom 740 to the MFJ 297 is as follows.

Icom pin # 1 to MFJ socket A mic pin #3 (Mic Audio)
Icom Pin # 7 to MFJ socket A mic pin #4 (Common Ground)
Icom Pin # 6 to MFJ socket A mic pin #2 (PTT GND)
Icom Pin # 5 to MFJ socket A mic pin #5 (PTT Hot)

Other information:

MFJ User manual:

http://www.mfjenterprises.com/man/pdf/MFJ-297.pdf

Icom 740 user manual. (Mic wiring diagram)

http://dw.hampedia.net:8080/download...740_manual.pdf

Other MFJ 297 "unused" socket A pins and thier function:

MFJ mic pin # 1 = No connection
MFJ mic pin # 6 = No connection
MFJ mic pin # 7 = Freq/ up down
MFJ mic pin # 8 = +8 VDC (!!!Be extremely careful not to feed any voltage from this pin into the rig!!!)

Hope that helps.

KD4OVM · #8 11-08-2009, 02:41 AM

Will give it a shot

Thanks a bunch

WB2WIK · #9 11-08-2009, 02:43 AM

Quote:

Originally Posted by KC8VWM

Icom IC-740 8 pin mic wiring / pin function as follows:

Pin # 7 = GND (Shield)

Pin # 1 = Mic Audio

Pin # 5 & #6 = PTT circuit. TX ON/OFF

Note: The PTT circuit on the Icom 740 (pins 5 & 6) utilizes an isolated PTT switching circuit that does not use the ground braided shield as part of the TX function.

It appears the reason the TX function is configured in this way has to do with how the VOX circuit works. The VOX probobly operates without the need of pushing the PTT button down when VOX is activated on the radio.

Seems the MFJ 297 has a "switch selector" which accomodates Icom rigs. You need to set this selector to position "A"

This is not a typical microphone and I am beginning to understand exactly why you may need help configuring it.

Caution:

One needs to exercise extreme caution wiring this microphone because the microphone has two output connectors which at a glance might suggest to someone you can connect this microphone to two seperate trancievers at the same time but DONT DO IT! The manual states this will damage BOTH trancievers!

The mic output socket you are concerned with wiring is socket "A".

The wiring from the Icom 740 to the MFJ 297 is as follows.

Icom pin # 1 to MFJ socket A mic pin #3 (Mic Audio)
Icom Pin # 7 to MFJ socket A mic pin #4 (Common Ground)
Icom Pin # 6 to MFJ socket A mic pin #2 (PTT GND)
Icom Pin # 5 to MFJ socket A mic pin #5 (PTT Hot)

Other information:

MFJ User manual:

http://www.mfjenterprises.com/man/pdf/MFJ-297.pdf

Icom 740 user manual. (Mic wiring diagram)

http://dw.hampedia.net:8080/download...740_manual.pdf

Other MFJ 297 "unused" socket A pins and thier function:

MFJ mic pin # 1 = No connection
MFJ mic pin # 6 = No connection
MFJ mic pin # 7 = Freq/ up down
MFJ mic pin # 8 = +8 VDC (!!!Be extremely careful not to feed any voltage from this pin into the rig!!!)

Hope that helps.

Except all that doesn't divulge which color wire from the MFJ base connects to what: It assumes you have the connector installed, which he said he did not.

Not sure how that helps, but maybe it does!

W0GI · #10 11-08-2009, 03:13 AM

Quote:

Originally Posted by WB2WIK

Except all that doesn't divulge which color wire from the MFJ base connects to what: It assumes you have the connector installed, which he said he did not.

Not sure how that helps, but maybe it does!

It is all the information you need, if you can use an ohm meter. If using an ohm meter is too hard, then buy a new cable. Who knows for sure if MFJ even uses the same color code on production runs?

They really don't have to, as this is a plug and play adapter. If the color code was a given, it would be in the manual. The important part is that each input pin go to the correct output pin. There is no way to depend on color, as MFJ may use a different multi conductor cable at some point in production with different colors to make the adaptor cables.

I guess I am being a bit too blunt, but if you can't trace the pins of the existing connector, to the actual colored wire on the other end, then buy a new cable. That is why they sell them, at a good profit.

If you want to learn how to trace circuits with an ohm meter, then learn, but don't expect people to do it for you, or somehow know what the color is.

I guess I am getting a bit tired of reading posts almost everyday like, "My Kenwood doesn't transmit, what is broke?".

If radio shops could fix them with no information, and no need for expensive test equipment or troubleshooting time, they would be real happy.

KC8VWM took alot of his time to post alot of information, and to say it wasn't a good answer is baloney. Sorry, but help doesn't mean doing it for you.

I'm not going to put down someone that doesn't have a desire to trace a microphone cable. That's fine with me, but don't expect free service from the ham community. If you want to learn, plenty of people will help like KC8VWM did. If you just want people to waste their time, so you don't have to buy a cable, then that's another matter. All the info is there, every bit, and it just requires a VOM.

Ok, I'm done griping now.