Maestro & FHM-2 mic issue

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  • Problem
  • Updated 2 months ago
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  • (Edited)
My friend just received his new 6400 and Maestro from FRS.

He also purchased the 8-pin modular mic cord so he could use the FHM-2 supplied with the 6400 on the Maestro.

He proceeded to connect the 8 pin modular mic cord to the Maestro. The mic will key the radio, but there is no transmit audio. Not being sure if he missed a setting somewhere, I took a ride over to his place to assist in determining what the issue is.

All settings were correct. Maestro set for MIC1, bias on, mic level at 100.

We then took the FHM-2 mic and reconnected the modular to 1/8” / RCA cable. We plugged it into the 6400. The mic worked fine.

We then plugged the 1/8” plug into MIC2 on the Maestro, and used a 1/8” male to RCA female adapter to connect the PTT lead. Set the Maestro for MIC2. The mic keyed the radio and modulated it just fine. Bias on and off makes a noticeable difference in mic gain level.

I spent the next hour or two troubleshooting the issue further. Examining the optional mic cable shipped for use with the Maestro, it is nothing more than a straight thru cable. I ohm’ed it out pin for pin, and it checked good. I then connected one end to the Maestro, and took measurements at the other end. PTT, 5V, GNDs, and MIC pins check out fine, as per the Maestro manual. I can take a tone generator and inject a tone onto the MIC pin (pin 5) and modulate the radio. However, if I measure the MIC pin with a voltmeter, regardless of the BIAS setting for the Maestro, at no time is there any bias voltage present.

If I perform the same test at the modular end of the Y cable supplied with the 6400, while plugged into the Maestro MIC2 port, the BIAS voltage is present on the MIC pin when turned on, and absent when turned off, as expected.

While testing for the presence of BIAS voltage, the source of the problem became clear:

The cord supplied with the FHM-2 and 6400 has MIC audio on pin 3 of the modular end, and the cord supposedly for the Maestro has MIC audio from the radio on pin 5 (as expected, since it is a straight thru pinout). The other function pins are also layed out differently between the two mic cables.

The coiled cord shipped with modular connectors on both ends is obviously straight thru. The radio mic cable is obviously a custom pinout between different connectors. So the question is:

Did FRS ship him the wrong cable to use the FHM-2 on the Maestro?

Or did they ship him an older version FHM-2 that used a different pinout scheme at the bottom of the mic itself? (And accordingly, a different version mic to radio cable?)

And more importantly, is the Maestro defective, in that there is no mic bias voltage present on pin 5 (MIC), regardless of he BIAS setting in Maestro?

Eric
K2CB
Photo of K2CB Eric Dobrowansky

K2CB Eric Dobrowansky

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Posted 3 months ago

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Photo of Tim - W4TME

Tim - W4TME, Customer Experience Manager

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Official Response
The issue you are experiencing with the FHM-2 microphone provided with the FLEX-6400(M) and FLEX-6600(M) not working when used on a Maestro connected to the MIC-1 connector is due to a manufacturing issue from our supplier.  This manufacturing oversight was brought to our attention and we are actively working to correct the problem.  In the past, we provided a replacement mic head but unfortunately, we are currently out of stock of them.  

Due to the estimated time to receive the new hand mic we are in the process of modifying existing FMH-2 microphones so they will work with the Maestro and all FLEX-6000s.  We expect to have the modified microphones available in a few weeks barring any unforeseen circumstances that may delay delivery.  If you are experiencing this issue with your Maestro, please open a HelpDesk support ticket so that you will be automatically placed in the order fulfillment queue when they become available.

We apologize for this oversight and expect to have this situation corrected as quickly as possible.  Thank you.