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Author Topic: Remaining headlight problem  (Read 2780 times)

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« on: May 16, 2012, 03:38:56 PM »

Have re soldered all connections, checked all sub circuits for continuity, light bulb lights when directly hooked up by passing device in gray wire from connector plug under cab and swapped out tender with 2 other, same type engines, and they work correctly. Manufacture has no answers. The problem stays with the locomotive, as swapping other working tenders does not correct the problem. Problem is in neutral, light does not come on dim, and when in forward, only comes on dim. Reverse light works OK, but headlight is out instead of dim. When hard wired by passing some sort of device in series with the gray wire to the headlight, light is on all the time on what appears a little less than bright except when cancelled by F-0. The device in the line must be bad, but don't know what it is or where to get one, except to order a complete wire harness, and as of now don't even know if it's available. It is medium blue in color, is about .060. dia, about 3/16" long with 3 black bands in the center and a black band on each end, one of them a little narrower than the other. I thought it might be an inductor since all colors are the same. Meter shows a resistance of .10 on the 20K scale when checked.  This is the only thing I can think of as to be the problem. Any answers out there. Decoder working fine. BILL
« Last Edit: May 16, 2012, 06:12:20 PM by blf » Logged
Jim Banner

Enjoying electric model railroading since 1950.

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« Reply #1 on: May 16, 2012, 05:17:19 PM »

I assume your mystery device is mounted on a printed circuit board and suspect it is a zero ohm resistor.  A zero ohm resistor is essentially a piece of wire wrapped in a shell to make it the same size and shape as a regular resistor.  Zero ohm resistors are used where one printed circuit trace must cross another but the manufacturer does not want to go to the expense of using a double sided board.  If you were adding components to such a board by hand, you would probably just use a piece of bare wire on the top of the board (the side opposite the copper traces.)  But automatic insertion machines are designed to handle resistors, among other things, so a zero ohm resistor is often used place of a piece of wire.

So what would keep such a simple device from working?  Here are some things you can check for:
- cold soldered joint at one of both ends of the device.  Use iron to resolder.
- cold soldered joint where wires connect to board.  Use iron to resolder.
- broken printed circuit trace.  Check with strong magnifying glass or trace with solder from end to end.
- still no joy?  Bypass the whole mess with a piece of wire.

If your mystery device is NOT on a printed circuit board, then it could be a micro fuse.  The 0.1 ohm resistance could be believable for a micro fuse, but not when it is measured on a 20,000 ohm scale.  Try measuring it on a 10 ohm or even a 100 ohm scale.


P.S. I hope you will take the time to post your findings when you finally get this problem solved.  Learning the solution to these odd ball problems is good learning experience for all of us.

« Last Edit: May 16, 2012, 05:20:29 PM by Jim Banner » Logged

Growing older is mandatory but growing up is optional.

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« Reply #2 on: May 16, 2012, 06:09:54 PM »

Jim: Hoped someone like you would respond to this problem. The device I described is in line with the wire going to the headlight,and is in the locomotive by the gearbox with shrink tubing over it.  Removed it to see what it was. Looks like it is directional due to the different thickness of black bands on the ends. Thought it might act like a resester to change current flow to the bulb. Sorry I'm a electrical Dunce with this new stuff. Have re soldered all connections already. Wired around the object and the headlight lights up but doesn't respond to the dim and bright functions from the decoder except F-0. Is there a source for this type of devise for hobbyists in the electronics field? Does the color coding have any meaning like on a resister? Still don't know what it is to even try to replace it. I'm stumped. Thanks for the input. Bill

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« Reply #3 on: May 16, 2012, 10:44:24 PM »

Could you post a photo of it?

Jeffery S Ward Sr
Pittsburgh, PA

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« Reply #4 on: May 17, 2012, 12:22:43 PM »

HI Jim: Don't know how to post photos but will describe item. Sounds like it is a 0 ohm devise, but don't understand its function if soldered in line to the bulb. When the devise is by passed, the bulb lights at the same consistency at all times regardless of eng operation unless killed with F-0. Item is about 3/16" long and a #4 shrink tube just slides over it (about .060 in dia), medium blue in color with bumps on both ends. Three black bands in middle (0 value ?) with black bands on each end, one narrower than the other. Wire extends out about 3/16" on each end. Do you think the different widths of bands on end make it a directional devise. If it's a bad fuse, would it still light on forward movement. Might have connected backwards for a time, but switching direction didn't make a difference. Lights worked fine untill I inserted a re programed chip. Had all three bells changed. Replaced chip with a original with no change. Decorders all work fine on the other two engines. When I was a inspector with IHC, bad ground connections played havoc with the light operation in the trucks. But there isn't a ground to deal with after coming out of a decoder is there? Maybe a bad pickup creating resistance. Bill
« Last Edit: May 17, 2012, 12:27:35 PM by blf » Logged
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