Galaxy DX 2547-Resister Burning Out

[HerbBE]

Hi. I hope someone can give me an idea of possible causes for the same resister burning out as soon as the radio is turned on. All other features on the radio seem to work okay, except this constant burned resister in the meter light circuit. I have replaced it twice, so I know it is something besides a defective resister.

If you can view the attached schematic, the unit receives 12v up to the resister as indicated on the multimeter. I am assuming everything in the system is okay up to this point. J20 takes the power from the resister to the smaller LED board via three wires. L+ on the smaller LED board gets 13.8v(12v) from the orange wire on J408.

At this point, I am guessing that a transistor or resister on the LED board is pulling/shorting more power than the small 47 OHM 1/8 watt resister R282 can handle. I don't want to start removing transistors/resisters to test them if I am not on the right track.

Any suggestions?

 

[nomadradio]

That's a puzzle. R282 leads to the meter light, and nothing else, looks like to me.

Schematic link is on this page.

[URL]http://www.cbtricks.com/radios/galaxy/dx2547/index.htm[/url]

73

 

[Robb]

Looks like you need to inspect that board carefully and look for a dead short.
Only way it could fry.

 

[OldTech03]

After replacing the resistor does the light come on or does the resistor puff instantly? If it's instantly then clearly as Robb said there is a dead short between the resistor and the bulb.

 

[Robb]

Another thing: why didn't your radio's fuse pop?
A dead short should have taken the fuse.
Curious . . .
Better make sure you have the right sized fuse in the fuse holder too.

 

[2NC995]

Another thing: why didn't your radio's fuse pop?
A dead short should have taken the fuse.
Curious . . .
Better make sure you have the right sized fuse in the fuse holder too.

Wouldn’t the resistor be limiting the current (as well as soaking up a lot more than 1/4 watt)?

 

[HerbBE]

Thanks for the ideas!

Okay. Today I removed the old transistor (R282) and replaced it with a new (tested) 47ohm 1/8 watt resistor. I checked for loose wires, solder bridges, etc--all clear. Multimeter reads 12v at the resister and on the J20 terminals-G to 13.8v. The 8v to ground on the J20 terminals reads 8v.

This time, I removed the jumper from J408 at the J20 terminal. I then plugged the radio in and the resister didn't burn. Then I pushed the on/off button on, and again the resister didn't burn. So far so good!

Can I safety assumed that the problem is passed the J20 terminal, and most likely on the LED board? I am pretty sure if I reconnect the J20 and J408 terminals, the resister will blow. What can I test next?

 

[2NC995]

Sounds to me like you’re on the right path.

The sub-board being isolated from the rest of the radio is what I would want for finding a short.

 

[sunbulls]

Did you try removing the bulb before reapplying the terminals? The leads inside the bulb may have welded themselves together. Christmas tree light syndrome.

 

[Shadetree Mechanic]

Is it possible to plug the jumper in backwards? I suppose it only goes in one way. You could unplug all the connectors from the LED board and then plug in J408 and turn it on. If the resistor is ok, plug all the other plugs into the board one at a time and you might find one that pops the resistor. Or you might find that the radio suddenly works correctly. I have "magically" fixed machines at work just by walking up to them. Haha.
Chris

 

[HerbBE]

Did you try removing the bulb before reapplying the terminals? The leads inside the bulb may have welded themselves together. Christmas tree light syndrome.

I have tried several incandescent and LED lights. The lights are all okay.
I even temporarily wired the bulb directly into the J20- J408 jumper. It lights.

Sounds to me like you’re on the right path.
The sub-board being isolated from the rest of the radio is what I would want for finding a short.

Yes, this is what I was thinking. This meter light seems to be a problem in a few of these Galaxy DX 2547s, and I thought someone figured this out already!!!! I was looking for some short cuts!!!

Is it possible to plug the jumper in backwards? I suppose it only goes in one way. You could unplug all the connectors from the LED board and then plug in J408 and turn it on. If the resistor is ok, plug all the other plugs into the board one at a time and you might find one that pops the resistor. Or you might find that the radio suddenly works correctly. I have "magically" fixed machines at work just by walking up to them. Haha.
Chris

I have checked and rechecked, schematics and photographs of the jumpers and all of the boards. I am sure they are in the correct way. I was thinking about unplugging all of them as you pondered, and I will probably try this, but I am concerned about how this will affect other components, even on this same circuit. For example, the circuit may need another circuit to supply v to a transistor to open.

 

[2NC995]

For example, the circuit may need another circuit to supply v to a transistor to open

Q402 completes the circuit....but if there’s a direct short it would seem like it had to be between J400 and the lamp?