SW7 HO scale light post broken

Model Railroader Electronics and DCC
1

I have an Athearn 25 year old SW7 diesel switcher where the light post has come off the engine chassis. I have tried a few times to either solder it on or to glue it on to no avail. It alsways gets loose and falls off again. And I realized that I cannot glue it as the light post is the partly the power for the light. Athearn says they do not have any of these chassis and offered a different more modern one for me to purchase. I do not know if the new one will work as it may have completely different layout than the old one I have.

Does anyone out there have any ideas on how I can get the light post securely attached to the chassis again?

Also, does anyone have a good idea for a decoder that will fit this particular engine? This engine was not built for DCC and does not have any kind of light board or decoder board on it.

Thanks,

George

2

Drill a hole and tap for a small screw - fixed an issue with a Mantua loco I had.

Decoder is probably gonna be a process of:

  1. Isolate motor, lights, etc. from the frame.
  2. Connect decoder power wire (err, red and black?) to left and right pickups
  3. Connect motor wires (orange and … Errr, slate?) to motor
  4. Connect light functions (white, yellow, etc) to each light (and blue common positive)

As for the model of decoder, I recall NCE and TCS had a couple N scale ones that handled an amp or so - I’d start looking there.

3

I’ve converted several Blue Box Athearns with decoders. One of the first things I do is to remove the light mounting bracket. Then I use LED’s mounted in the light opening and wired to the decoder.

As far as decoders, you will need to check the different ones to see what effects are available and pick one that meets your criteria.

Good Luck, Joe

4

I agree with Joe. Use LEDs, especially with DCC. Better light and longer life. Just don’t forget the resistors.

Dave

5

The older Athearn motors can draw well over 1 amp. Check the stall current and make sure the decoder will handle the max current. You must isolate all electrical connections from the chassis when installing a decoder. If any of the decoder wires other than red or black connect to the chassis the decoder is toast. Either the black or red wire can connect to the chassis and the other to the truck power pickup.

Mel

My Model Railroad
http://melvineperry.blogspot.com/

Bakersfield, California

I’m beginning to realize that aging is not for wimps.

6

To repair the light post/bracket, I use a spring loaded center punch. Place the bracket over the peg on the frame and support the frame. Place the center punch in the center of the peg and push down on the center punch until it ‘fires’. Repeat the punching process until the peg has spread out enough to hold the bracket.

7

Joseph,

Since I am not knowledgable about electricity, How to I wire the decoder to the lights? Right now there are no lights, I have the white wire from the decoder soldered to the chassis and the engine works. I would like to have lights front and back, but do not know how they are wired from decoder wires.

Can you help?

8

Hi Georgep,

Your decoder is not wired to the locomotive properly if the white wire is attached to the chassis. The white wire should go to the front headlight with the blue wire being the other half of the light circuit.

Below is a wiring diagram for a typical decoder. The brand doesn’t matter since almost all decoders use the same colours for the same functions. Your decoder may not have as many wires.

Note that if you are using an LED the polarity has to be correct. Test the light before making any solid connections. If it doesn’t work try reversing the wires.

Dave

9

You do know that you have to isolate the motor from the frame?

10

Seeing what Georgep is trying to accomplish, I would go with a simpler decoder. That Loksound decoder is great, but for a first time decoder install, it may look a little confusing, as not all decoders look like that.

I’d go with the Digitrax DH126D, it has the full harness for a complete hardwire. I know it’s only a 2 function decoder, but it will give him front and rear lights.

http://www.digitrax.com/products/mobile-decoders/dh126d/

Open the link, and in the upper right hand corner is the instructions, and wiring diagram. Not quite as daunting as an expensive ESU. The instructions go through everything.

Mike.

11

Hi Mike,

I didn’t intend to suggest that the OP go with a Loksound decoder, although there’s nothing wrong with starting out with a decent decoder. I used their illustration just because I knew where to find it. I did mention that the OP’s decoder may not have as many wires.

Dave

12

Hey Dave, I was not trying to “knock” your post at all, just trying to give the OP another way, as it seems that the OP was starting out with DCC as I was a few short years ago, starting with Athearn locos.

I had it easy to start with as Digitrax, at that time, had the DH123AT, which was all set up as kind of “plug & play” for Athearn locos.

Mike.

13

Thanks for posting that diagram, Dave. I have to do a DCC installation on a Bowser steam locomotive for friend, and while the instructions with the decoder explains the basic hook-up, the part about adding lights seems a little vague. That diagram really helps, as I’m otherwise electrically-challenged.

What I don’t see, though, is the resistors for the LEDs: does it matter in which LED wire they’re installed? My instinct (mostly just stinks in this field) tells me that they should go in the non-blue wires.

I don’t want to louse things up, as I told my friend that I couldn’t find suitable LEDs (I really couldn’t) so he said to just leave that and he’d take care of it.

However, I found a site in B.C.offering very small (less than .025") LEDs, which will be perfect in modified MV Products lenses. I want to be able to surprise him with fully-installed working lights.
When I received them, I at first thought that I’d been ripped-off, as the LEDs weren’t readily visible until I removed them from the clear plastic bag in which they were contained. They’re actually small enough that you could do caboose marker lights with a separate LED for each lense. This is probably news to only me, but I am quite impressed. I tested one using a AA battery with not too much life in it, and got a fairly bright light, and I do have the resistors for the lights in the locomotive.

Wayne

14

Hi Wayne,

It doesn’t matter which wire you put them in but I always try to put them in the same wire just for consistency. If you always put them on the + wire you will always be able to quickly see which wire is which.

Are the leads on your LEDs coloured red and black or just plain copper? If they are plain copper I suggest using a paint pen to colour at least one of the leads. The copper wired LEDs usually have one lead longer than the other (I can’t remember which) but that doesn’t do you a lot of good if you have to trim the leads shorter.

A couple of suggestions if I can: The leads break off the LEDs very easily so the less handling you do the better.

You could do that but you would have to make sure that each LED is insulated from the others. A coat of nail polish will do the trick. The challenge would be to get each of the LEDs correctly aimed at the lenses. If they aren’t pointing straight at the lenses you won’t get a lot of light coming through the lens.

An easier solution is to take a 3mm round tip LED and file the tip down so that it will fit inside the barrel of the marker lights. If you fill the marker light with epoxy or canopy glue before inserting the LED the single LED will light all three lenses quite nicely. I put my 3mm LEDs in a drill chuck and spin them slowly while holding a file against the side of the tip of the lens. If you are doing marker lights on a locomotive there may not be space for the body of the 3mm LED, but if you are doing cabooses space is not a problem.

Regardless of the size of the LED, you may want to experiment with higher value resistors than the usual 1K ohm. At 12 volts with a 1K resistor the LEDs are very bright a

15

Thanks for that additional information, Dave. The LEDs have a black wire and a red one, and I had planned on coating the attachment of them to the LED with either epoxy or brushed-on Dullcote, as they’ll be installed in metal headlight castings. I’m also using MV lenses, and they suggest to drill a small, centered hole in the back of the lense’s reflective coating, and inserting the LED in that. Unlit, it looks like, what else?, but an unlit bulb in a reflector. Lit, they make for a very realistic appearance.

Well, before finding those LEDs, I was pretty nervous about having to do only part of the job, but still having to leave the rest of it useable for someone else to finish. This way, as long as I do a decent job, the loco will be ready-to-run as soon as my friend does the programming. I hope to deliver it on my first trip to the States in the coming year, as I visit him fairly regularly (not in the winter, though).
And, yes, I’m a little shocked, too, but at one time I put lights in my locos and in some structures, too. I also did quite a few locos, mostly brass, for friends who wanted them repaired or detailed, and painted, and all too often, with lights, too.

I may even add these LEDs to one of my own loco projects (I have 3 Bachmann Consolidations to turn into specific CNR locos, two Athearn Mikados, probably also destined to become models of specific CNR locos, a Bowser K-11 Pacific to become a TH&B Pacific, a John English Pacific for my own freelance road, and parts from a Tyco tender-drive Consolidation to make into a TH&B Consolidation. That last one will likely use only the loco frame and drivers, with much of the rest mostly scratchbuilt. It’ll get a can motor and NWSL gearbox, too,

16

Wayne,

That’s quite a fleet of locomotive projects! You must have a big roundhouse![swg][(-D]

My critter is DC and it uses an LED (two actually). All I did was install a bridge rectifier and it seems to work fine. However, the starting voltage for my critter is a bit on the high side. My solution may not work for you at very low speeds if there isn’t enough voltage.

Dave

17

Hi Dave,

I went out to install some new lights in this locomotive I was telling you about with the broken post. I wired it like you show in your diagram. I put in front and rear 12 volt incandescent lights. When I got done, I put the engine on the track, punched it up with my DCS50 and moved the throttle to get it going and I got nothing. It was running the last time I used it, but today after the lights install it is not working. White wire to front headlight, yellow wire to rear light and the blue common to both that gets everything together. When I came in back into the house from the train room, I realized that I did not press the 1 function button to turn the lights on in the engine. But the engine still does not run. I tested the bulbs before and after the install and they both worked fine. I also pulled up the engine on JMRI and wrote the last setup to it, and it seemed to be writing to the CVs. Where did I go wrong.

18

Hi Georgep,

Sorry to hear that you are having trouble with the engine.

Dave

Edit: I deleted the rest of the post because I was totally off base.

19

OK, DCS50? That is the Digitrax Zepher. I would do a reset on the decoder, and then try everything again.

I’m sure RRinker (Randy) will see this and help you out.

Mike.

20

It’s not a system issue, it’s a decoder issue.

So where are the rail pickup wires connected (the red and black)? The old Athearn harness Digitrax sold for the decoder connected one side to the light post which was broken off (yet another reason this was always a bad idea). Also, if you disassembled the whole thing to the point of removing the motor - is there tape in the bottom of the frame to keep the motor from touching the frame? And are both motor wires still connected (orange and grey)?

–Randy