Hi folks,
A lot of the posts on this forum are in the form of a question, seeking advice on how to fix problems. Well I have a question from the opposite end of the spectrum. I accidentally fixed a problem, and I want to know if anyone can tell me what I did!
Here’s the story:
I recently bought (well, a while ago now) one of the first run of Intermountain HO scale SD40-2W locomotives, the DC/DCC non-sound version. These locomotives are quite notorious for having a very poor ditch light design (i.e. they’re just super dull, as they’re designed with an LED below the deck that transmits light into the clear plastic castings). I, however, didn’t get to really even appreciate that the ditch lights were dull, as mine didn’t work AT ALL. Nothing. Now I’m just running in straight DC, but when I powered up the headlights (at the appropriate end) and numberboards lighted, but no ditch lights at all.
After many months of thinking “well that sucks” or “maybe they’re just soooo dull I can’t see them at all”, I finally decided to pull the loco apart and try to address the problem. I checked all the wires, making sure nothing was crossed or shorting, and that everything was actually connected where it should be.
No problems. All the wires leading to the LEDs looked in order. So the question then became, where is the source of the problem? Are the LEDs not receiving power through the wires (which didn’t appear to be the problem), or is power not getting through the PC board to which they were wired?
I would have liked to use a voltmeter of some description to check some connections, but didn’t have one around. So I decided on a different strategy. I thought I’d take two wires from my power supply, set to a very low voltage (as I was about to bypass all the resistors), and try to power the lights.
I carefully applied power to the points where the LEDs connected to the PC board. Nothing. I tried each light separately