GM300 Tech help needed...

[Woody_99]

Hey guys, I've got a GM300 here that came from a 911 center. Radio had a mic "plug" in it, as if it were in repeater use. In-line fuse was blown, and upon testing, the board fuse was also blown. I replaced the board fuse and the radio powers on, now and appears to work fine.
Model D43GMC29C2AA

First problem.... every high-pitch acknowledge and turn-on beep is followed 4 seconds later with a short low-pitch beep. Radio works fine.
?? What's up there??

Second problem.... radio puts out 12w on the meter, but gets a hot heatsink rather quickly, less than 45sec.
Notes on this are: Service RSS setting for TX POWER was about 64...(it's in the 80's on my other GM's.)
It appears the adjustment/locknut in the rear of the heatsink/PA has been moved or turned.... ? What exactly is that nut and how to adjust?

I'm not a tech, just a flunkie, so if anyone could fill me in, I'd appreciate.
thanks!

[jackhackett]

Well I can tell you what the nut is for.. it's the mounting nut for one of the transistors, either the driver or final, depending on if it's a high or low power model (would be the driver on a D43).

[Doug]

Woody,
The settings in the service menu are basically just relative to that radio.
There is no fixed output power set to that value.
Doug

[Woody_99]

Well, I went ahead and cranked it up to 83-84 in the RSS and got about 45.6 watts going now. Still gets hot quick, but not any quicker, and didn't explode...

Low-pitch beep 4-sec after the hi beep persists....
I assume it is a tuning/setting/something?

tnx for the help thus far!

[Ed]

First problem.... every high-pitch acknowledge and turn-on beep is followed 4 seconds later with a short low-pitch beep. Radio works fine.
?? What's up there??

Second problem.... radio puts out 12w on the meter, but gets a hot heatsink rather quickly, less than 45sec.
Notes on this are: Service RSS setting for TX POWER was about 64...(it's in the 80's on my other GM's.)
It appears the adjustment/locknut in the rear of the heatsink/PA has been moved or turned.... ? What exactly is that nut and how to adjust?

First: I Think the GM-300 stands in repeater mode.

Second: Repeaterradio's power-output is (mostly) adjusted for duty cycle. The heat problem also exist on a faulty antenna (not tuned/defect/broken cable).

1 & 2 can be changed by RSS..

For a non-techie you could repair a defect Motorola.... Thats much better as a Motorola techie who could'nt repair a Motorola!


Ed

[n5tbu]

The low pitch beep could be the alarm,either ground the alarm pin or program to null in the "other assessory" screen.

[E911EMT]

The beep could mean a error in radio... I would call the Big M and ask Motorola about it...

[Woody_99]

...............and the Big Kahuna award goes to......

N5TBU!

It was the Emergency Alarm and sends on the pins.... guess the radio was a link/alarm.

Still don't like the heat this thing generates. Is a VHF rig hotter than a UHF?? None of my UHF GM radios heat as quick as this one does.

FINAL question... how do I get it to ENCODE QCII? Decode works great, beeps/flashes call and such, but I've not figured out the Encode... I have it set as signalling TX on a channel, but to no avail using a desk mic.

Thanks folks!

[pmoore40]

Jumper pins 7 and 9 on the 16-pin connector on the back and it will solve the low pitched tone on start up.

[kcbooboo]

MaxTracs, Radiuses, and GM300s ALL get hot when transmitting, and it doesn't seem to matter if you've adjusted the power to 5 watts or 45 watts. Also, they don't like to transmit for too long, even with LOTS of cooling air flowing over the heatsink. While there's no temp sensor on the heatsink, there is one somewhere else inside the radio, and after 20-30 minutes of transmitting, no matter what the power level, the radio's micro-processor will think the radio is getting too hot, and start lowering the power, eventually setting it to zero. When you un-key, it will reset and transmit for a minute or more, then repeat the shutdown process. Very annoying, especially since the power amp is nice and cool. But that's just the way it goes with these radios. Keep them well ventilated!

Bob M.

[Will]

The GM300 does have a tempature sensor on the PA, and an extra contact on the logic board for the PA cable. You may have to have that PA tested for spurious power, that would explain the overheating. Also prolonged heavy use will dry out the thermal grease used on the transistor mounting surface to the heatsink causing very poor heat transfer.

There is a note about a larger heatsink available for the Radius/Maxtrac and GM series PA's, but it costs about $75 + the labor to switch it out. I have them on several repeater GM transmitters.

[kcbooboo]

I know that the MaxTracs and Radiuses do NOT have any temp sensor in the PA. I was "assuming" the same for the GM300 but haven't worked on any of those. However, even if you keep the heatsink nice and cold, these radios were originally only designed for something like 10/10/80 duty cycle, i.e. 10% transmit, 10% receive, 80% standby, and that seems to be over a rather short time interval. They just don't like to be used in repeater service where the transmitter could be on solidly for 30 minutes or more.

How come the Japanese radios manage to stay so much cooler, even at low power settings?

Bob M.