I'll do my best to describe what is happening. Its just too late for me to back in and work on it any more tonight, but here is the problem.
A guy from work brings me this radio and said that he thinks the finals are burnt because it is showing less than a watt on his meter. I open it up and check the voltages on the resisters in front of the finals that receive the power from the VR's. I was told by Galaxy a couple years ago that this is the easiest way to check the voltages on the mosfets. If there is around 3.5 volts and when you turn the pots that control the voltage to the finals if they adjust up and down then there most likely alright.
What I found was they are adjusting but only reading 0.83 volts or so. This goes the same for both finals and the driver. Of course all three of these are the 520's.
Next I got to looking at the pre-drivers. I found the resistor (r246) that goes to ground from the pre-driver(Q51)(NPN) was burnt and the pre-driver was not working properly. I replaced the pre-driver, resistor and the cap that is also goes to ground along with that resistor.
Fired it back up and smoked the resistor again and the transistor.
I'm thinking my next step is to work my way back before Q51 and see if there something else not right. I see no tell-tale signs of anything else and this radio has not been volted or anything like that. A receive mod has been added but nothing stupid.
So does anyone got any ideas or has ran across this before? Or can offer some verbal assistance?
Thanks as always from A guy that probably shouldn't be messing with radios and know enough to get himself in trouble...
Jerry...
A guy from work brings me this radio and said that he thinks the finals are burnt because it is showing less than a watt on his meter. I open it up and check the voltages on the resisters in front of the finals that receive the power from the VR's. I was told by Galaxy a couple years ago that this is the easiest way to check the voltages on the mosfets. If there is around 3.5 volts and when you turn the pots that control the voltage to the finals if they adjust up and down then there most likely alright.
What I found was they are adjusting but only reading 0.83 volts or so. This goes the same for both finals and the driver. Of course all three of these are the 520's.
Next I got to looking at the pre-drivers. I found the resistor (r246) that goes to ground from the pre-driver(Q51)(NPN) was burnt and the pre-driver was not working properly. I replaced the pre-driver, resistor and the cap that is also goes to ground along with that resistor.
Fired it back up and smoked the resistor again and the transistor.
I'm thinking my next step is to work my way back before Q51 and see if there something else not right. I see no tell-tale signs of anything else and this radio has not been volted or anything like that. A receive mod has been added but nothing stupid.
So does anyone got any ideas or has ran across this before? Or can offer some verbal assistance?
Thanks as always from A guy that probably shouldn't be messing with radios and know enough to get himself in trouble...
Jerry...