Batboard

WHAT CAUSES MY GM 300 MONITOR LIGHT TO SAY ON ! THE PL 107.2HZ IS PROGRAMMED... BUT ANY SIGNAL(ON REC FREQ) WITH OR WITHOUT TONED PL WILL OPEN REC... NO MIC AND FORCED MONITOR RSS IS PROGRAMED TO OFF....HELP ME! WHAT AM I DOING WRONG !!!!????

In order for squelch to open on CTCSS tones, two conditions must be true: 1.) Hook pin on mic connector must be low(Gnd); normally this is provided through the single or dual contacts on the rear of the mic at the button, and 2.) Monitor mode must be disabled by using the Mon button on front of the radio(it toggles between mon-yellow LED on, and PL - mon LED off).
If either of the conditions above is false, squelch will open on only carrier on channel(in mon mode PL is disabled).

SCMR2242 wrote:WHAT CAUSES MY GM 300 MONITOR LIGHT TO SAY ON ! THE PL 107.2HZ IS PROGRAMMED... !!!!????

First clue.. " the monitor light on all the time" The monitor indicator should go out when the MIC hang-up stud is grounded.

What about the BUSY indicator? Is that ON without any received signals?

You said no mic. That's why. The hangup button can't be grounded if it's not there.

I MAY HAVE MISLED YOU... I HAVE TRYED THE HAND MIC PLUGGED IN AND GROUNDED TO CHASSIS.. NO DIFFERENCE...MONITOR STILL ON ... IN THE RSS THERE WAS A QUSETION ABOUT MIC OR NO MIC I ANSWERSED "N".. ASSUMING THATS WHAT THE QUESTION MEANS.(NOT TO FAMILAIR WITH MOTO RSS ANYWAY) ...THERE IS NOT A REC SIGNAL EXCEPT WHEN I PURPOSELY GENERATE ONE ON A HANDHELD ...

I HAVE SINCE PULLED OUT ANOTHER GM 300 AND READ THE CODE PLUG AND OTHER RSS INFO AND IT ACTS AS IT SHOULD... THE CODE PLUGS ARE IDENTICAL IN THE RSS READINGS.....MONITOR OFF WHEN MIC HUNG TO GRD... I BELIEVE I MAY HAVE A MONITOR CIRCUIT FAILURE...ANY SUGGESTIONS ... I ALSO USED THE REAR PLUG CONNECTOR FROM THE BAD RADIO IN THE GOOD RADIO AND I DIDN'T EFFECT THE GOOD RADIOS ABILITY TO WORK CORRECTLY...

WILL,
THERE IS NO REC LIGHT EXCEPT WHEN I GENERATE A SIGNAL FROM ANOTHER RADIO ...BELIEVE ITS OK ON THAT POINT

Time to get the schematic out and trace the hang-up signal. It probably goes through a diode or two for protection, then a transistor, on its way to the microprocessor or other big logic chip.

Sometimes these input lines get connected to the wrong voltage by people trying to do things with the radio that it wasn't designed for, then things go bad. Shouldn't take long to find, and will probably only cost a few pennies in parts.

Bob M.

THANKS BOB,
I THINK YOU'RE ON TO SOMETHING THERE...

APPRECIATE YOU TIME

Not that this is your problem, but the GTX mobile suffers a similar malady if someone attaches +12V to the rear panel PTT input, which only expects to be grounded. This voltage blows up a 5.1V Zener diode, causing it to short out, and that puts the radio into transmit mode as soon as it's turned on. The easy fix is to remove the diode; the correct fix is to replace it with a new one. So these kinds of things CAN happen.

It could also be a failure of the MIC jack in the front panel, or the circuit board it's soldered to, or the wires going to the logic board. All fairly easy to check with the service manual. You can swap control heads to rule that out. A voltmeter or scope should tell you where the problem is in very short order.

Bob M.

Like kcbooboo has said, your going to have to spend
some time running the circuit from the mic jack back to
the micro.

Some dumb techs have been know to clip a wire or cut
a circuit trace so this monitor would be on all the time.

You won't know where the problem is until you locate it.

Jim

THANK GUYS .... I FIXED IT !!!!!!!!! IT WAS THE MONITOR CIRCUIT .. A DIODE AND YES I'M SURE SOMEONE WIRED THE REAR 16PIN WRONG IN THE PAST ... THIS UNIT HAS HAD A ROUGH LIFE PRIOR TO OUR GETTING IT TOO....SERVICE MANUALS ARE REALLY HELPFUL ..HUH!!

THANKS AGAIN TO BATLAB GUYS ...

IT'S SO COOL WHEN YOU FIX YOUR OWN JUNK
THANKS AGAIN !!!!!!!!!!