Thread: Radio display light; Just wanted to share a repair experience

Howdy; Just recently bought a 2000 Grand Prix GTP. I have a couple of things I need help on, but before I asked for assistance I wanted to give a little. I bought this car knowing the radio display was blank, but I figured I could take the radio apart and either fix it or rig up a LED backlight somehow, or just read it off the HUD and set the presets and let it go at that. I found discussions already in the forum about the bulb, and instructions on removing the radio (so I won't repeat that). This odd incandescent lamp looks to had gotten hot, and the phenolic base the bulb is built into was cracked and starting to crumble (but the bulb filament was still intact). I took it out. Rummaging around my parts bins, I found a package of Radio Shack #52 lamps, cat. No. 272-1127. It's rated at 14.4 volts@ 100ma. the #52 is a small screw-base, and it just so happens that the OD of the base is the same as the ID of the circuit board hole. So I screwed it in a little, good tight fit, and soldered on board terminal directly to the bulb base, and soldered a tiny jumper wire from the opposite board terminal to the center connection of the bulb base. It's a lead knob on the bottom of the bulb. I put the plug in the back of the radio, and it worked! Yay! As , I was putting it together back in the car, there was wisps of smoke coming up from the radio! NOOOOO!! the light faded out. So I took it all back into my workshop and disassembled the radio. Easy to do, as there were a half-dozen or so torx screws. On the circuit board, there was a burned-out resistor. I could just make out the colors-3.9 ohms. Apparently, it's a sacrificial resistor made to fail if the light circuit faulted. 13.2 volts into a 3.9 ohm resistor is 3.4 amps, and the resistor is only 1/2-watt. 13.2v & 3.4A is 44 watts! What caused the fault- the bulb stuck slightly too low below the circuit board, and the center terminal happened to be positive/hot (50-50 chance of soldering in the bulb that way) and it shorted out against the radio metal cabinet. Well, a little tape fixed that issue. Replaced the resistor, and it's working perfectly!

The radio is all put back together and installed. It didn't occur to me to take a picture. But looking into the front of the chassis with the face plate removed, and the radio turned so the circuit board is up, the resister is on the component side, to the rear and to the right, just to the left of a large electrolytic capacitor. It's one of the larger resistors.