The Electronics Universe
The CB Forum => CB Radio Repair Forum => Topic started by: Mikes Radio Repair on January 18, 2016, 02:55:03 AM
-
Got a customers Galaxy DX2517 in for repair with a strange problem. When cold the output power is low but quickly increases. This radio belongs to a disabled person who is on a tight budget so he can't afford to put a lot of money in it. When first turned on in AM mode carrier power is 5 watts. If held keyed for about 45 seconds it goes to full output at 10 watts carrier power. It has a EPT690010D dual final PCB. What is strange is the output. Take a look at the spectrum analyzer views of the output, what the......... You could use this thing as a noise generator. Pictured span is 20 MHZ (20-40MHZ) directly hooked up through a 60db attenuator which the amplitude is adjusted for. Pictured in order: band A, D and F. Seing as the power problem is operating temp sensitive I figured I would hit it with a shot of freeze spray. It worked, kind of. If the pre-driver transistor is sprayed the power drops almost instantly to its low level and goes up as it warms back up. Well that was easy, or so I thought. Replaced it with a new one and it does the exact same thing, hmmm. Thought maybe it cooled a nearby part so I made a shield out of heat shrink tubing to stick on the spray nozzle. Power definately still changes when only the pre-drivet is sprayef. It has no effect on the spurious emissions. Any ideas? I can't spend much time on it due to customers financial constraints.
Mike
-
Hmm, not sure why the pictures loaded rotated 90º. Just tilt head to left. :)
-
Will get more time to look at this this afternoon. But would think it is some sort of thermal run a way but looking at the pics.
-
you might check out C218 for good measure, or either C216, or C220, might have gone leaky, but i've got an all too familiar sneaky feeling that it will end up being either L40, L42, L43, or L44, been there too many times to think it'll be any different in this case, lol
see what the output from the TX mixer looks like on the scope, if the signal appears to be missing or way off, then check L43 and L44, or if the signal is there, then look at the outputs of L42 and L40, should be a nice clean healthy 27MHz signal, maybe you'll be able to nail down which one it is pretty easy that way,
you can pull the bias check jumper board during this test so that the final section wont be working and getting hot for nothing,
:)
-
Ever figure this out i have an eagle 5000 and a friend had a 2290 that do the same thing will tx on 11M and be heard clear on the 10M band.
-
Stumped the panel i guess
-
Here is what mine looks like on an SA.
-
I found the problem and it is now fixed
-
I found the problem and it is now fixed
Well don't leave us hanging, what was the fix! :)
-
The factory added a very small surface mount resistor on IC5 phase comparator for some reason or by mistake on some radios. Mine was hidden under a suspect solder joint, after removing it the spurs are gone. A few shots of before and after on a spectrum analyzer.
-
?
-
First post didn't post. Is this the same PCB as in the DX99V2? EPT690010D?