Hello,
I have a Uhf GR1225 repeater that is built for 40 watts but set at 20 watts continuous duty. It now has trouble when transmitting...intermittanly the power comes up to only about five watts then it dives immediatly down to nothing. Once you try to key it again...same thing.
I have already swapped out power supplies with similar results. I'm looking for ideas befor I have to send it off to MOTO.
Thank you,
Bill
Gr1225 intermittant power out
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radioservice
- Posts: 95
- Joined: Thu Sep 20, 2001 4:00 pm
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jackhackett
- Posts: 1518
- Joined: Tue Jun 10, 2003 8:52 am
Sounds like a bad PA.
What generally happens is the output transistor overheats and the solder joints on the input and output tabs of the transistor get burned up. They can usually be fixed by sucking off the old solder, cleaning up the connections and resoldering using silver solder.
There are 2 chip caps from each tab to ground, you can usually clean them up with some solder wick and reuse them if you're careful, otherwise they need to be replaced. The transistors themselves are pretty sturdy and won't usually need to be replaced, I've had some where I've resoldered them several times with the same transistor, power comes right back up to normal.
On rare occasions the board itself gets burned, in which case replacing the PA is in order.
Now, to help keep it from happening again, once you get it fixed, turn the switch on the back of the power supply to put the fan on continuously, and you might want to lay the repeater on it's side exposing the bottom vents better. Also keep the fan and vents clear of dust, PM check it occasionally and blow the dust out.
These repeaters were meant for low duty cycle, ie. only keyed about 20% of the time, if it's in heavy use you're going to have this problem.
Turning down the power apparently doesn't make them run any cooler, there was talk here of adding an antenna matcher which is supposed to help, you might find more about that with a forum search.
What generally happens is the output transistor overheats and the solder joints on the input and output tabs of the transistor get burned up. They can usually be fixed by sucking off the old solder, cleaning up the connections and resoldering using silver solder.
There are 2 chip caps from each tab to ground, you can usually clean them up with some solder wick and reuse them if you're careful, otherwise they need to be replaced. The transistors themselves are pretty sturdy and won't usually need to be replaced, I've had some where I've resoldered them several times with the same transistor, power comes right back up to normal.
On rare occasions the board itself gets burned, in which case replacing the PA is in order.
Now, to help keep it from happening again, once you get it fixed, turn the switch on the back of the power supply to put the fan on continuously, and you might want to lay the repeater on it's side exposing the bottom vents better. Also keep the fan and vents clear of dust, PM check it occasionally and blow the dust out.
These repeaters were meant for low duty cycle, ie. only keyed about 20% of the time, if it's in heavy use you're going to have this problem.
Turning down the power apparently doesn't make them run any cooler, there was talk here of adding an antenna matcher which is supposed to help, you might find more about that with a forum search.
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radioservice
- Posts: 95
- Joined: Thu Sep 20, 2001 4:00 pm