GR1225 Tx Woes

[Jatla]

Hello All,
Does anyone have the GR1225 UHF Service manual Troubleshooting section? I have one that refuses to transmit. No obvious damage or physical faults. I believe that this may be a repeater controller problem. No continuous Tx light, just a very brief flash, and then nothing (even on local handset transmit). {Transmitter running into a dummy load to remove the duplexer from the equation. Monitor receiver sitting open carrier squelch to pick up any stray RF but nothing. That's why I'm thinking controller issue} The unit on forced monitor passes the CWID out to the internal speaker, but does not keyup. No programming changes since it functioned last. Unit was rarely used, and was not even noticed to be non functional until I happened to check it last week.

Any ideas? At least with the GM300 based small repeaters each component was seperate allowing for somewhat simpler troubleshooting without a manual. Swap parts and diagnose problem component.

Is there a way to key the radio up from the accessory connector on the back to at least check the RF portion? Is the pinout the same as an R1225?

Thanks,
jatla.

[txshooter]

FYI, these are great units, but sounds as if you may be having PA problems. This is pretty common on these units, Buy a replacement PA, I would almost bet my bottom dollar this would solve your issues.....

[wavetar]

The accessory pin-out is the same as the M1225 mobile, so grounding Pin 3 will activate PTT. You can also use the software in service mode to force the unit to transmit.

Todd

[Bat2way]

Your best bet would be to just replace the caps surrounding the PA transistor. They have probably had the solder melted away from them as a result of the PA running at full power. You can try to resolder them first, then reduce the TX power out to prevent the same thing happening again. A very common problem when the units were just programmed and set in place.

[Jatla]

That's a really interesting idea. I really thought that I would be able to monitor some leaking exciter RF upon keyup though. I don't hear anything. Also, the TX light only comes on very, very briefly; unless there is a monitoring circuit that will backoff the amplifier if something is amiss. I will confess that I am not too familiar with the 1225 series. But I will check this out, it may indeed be a "simple fix".

Thanks Again.

[Will]

There is a circuit in the R1225 that senses the control voltage going to the PA low level stages. If this control voltage goes above the normal value, usally due to a failed PA stage not amplifing, the uP will shut down the TX command.

Look for overheated componets and melted solder in the final PA stage. A good sign that the PA is not working causing the uP to shut down the TX command shortly after PTT.

[Batwings21]

Hello All,
Does anyone have the GR1225 UHF Service manual Troubleshooting section?

Speaking of this, anyone ever read the troubleshooting section? I like the one about hearing voices coming from the closet. (If you have a manual take a look its great) Also definitely try resoldering the caps first then turn power down to about 20 watts.

[Jatla]

The problem with the capacitors may be the issue. BTW how do you attach images that are not on an http site?

[chartofmaryland]

The pa is under 300 new and is a common stock part a many shops.

I can arrange one if interested.

CoM