@gunrunnerjohn posted:Pictures of the board would help, but it sounds like a typical fixed voltage DC power supply. The power device is probably a three-terminal fixed voltage regulator, a picture of the lettering on that part would probably tell the tale.
GRJ - Thanks for the suggestions. I'll have to remove the PC board to be able to see the device P/N. For the moment lets assume it's a regulator being used in the constant current mode. That puts a resistor in series with regulator's output and the LED load. The resistor then has two functions: providing feedback tot he regulator and a series voltage drop to the LEDs.
I need to determine if the LEDs are still functional. The LEDs need a dropping resistor for testing. Any idea on what size resistor for testing ? Maybe 1K to start with a 12 VDC supply ? I wonder how these LEDs are wired: series or parallel ?
If the regulator shorted out, the full wave DC would be applied to through the resistor to the LEDs. So LED forward voltage/current would be determined by the resistor size in part.
Another thought. The common wire (black) from the tracks I presume (I haven't traced it yet) is detached. The red wire from the roller pickups (need to trace that too) is attached. These are the inputs to bridge rectifier. There are huge blobs of solder on the PC pads which attach these input wires. It appears the input wires are "tacked" to the blobs during manufacturing, hence the blobs. There appears to be little to no solder on the bare black wire lead. There may be a barely discernable groove in one blob where the black lead might have been attached.
My point here is to determine where all the current flowed and why based on damage assessment.
