# Replacement Loco Bulbs



## SSBN743 (Dec 30, 2013)

I have an HO Athearn FP45 DCC with the Soundtraxx SD70 decoder installed - during removal of the shell I accidentally broke the headlight (what a pain in the a$$ removing the shell was BTW).

Anyway, I ordered some replacement LED's and am having some trouble. I ordered 1.8MM white LED's and they seem fine. They fit in the headlight hole and everything, however, they will not light. I got to looking at the documentation and discovered that they are 3.2V-3.6V LED's and the Soundtraxx decoder specifically calls for 1.5V LED's with no resistor.

I've looked and looked and I can't find a 1.5V LED anywhere; do I just have to use an incandescent bulb? Or does someone know where I can get the right LED for Soundtraxx decoders?


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## johnfl68 (Feb 1, 2015)

Which Soundtraxx decoder specifically is it, do you know?

The typical Soundtraxx decoders use a resistor with the LED.

In the Soundtraxx installation guide page 26 it says to use a 680-ohm resistor:
http://www.soundtraxx.com/manuals/tsuinstallation.pdf



> *Using LEDs*
> Tsunami decoders may be used with LEDs, which also require a resistor to
> be wired in series, typically about 680-ohms, 1/4W. Unlike lightbulbs, LEDs
> are sensitive to polarity. The minus (-) cathode end of the LED (the shorter of
> ...


It should work if you have the LED polarity correct and resistor. If the decoder is set up for 12v and you don't use a resistor, you will let out the magic smoke in the LED.

John


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## SSBN743 (Dec 30, 2013)

It's a TSU-GN1000 for EMD 710 (p/n 828052)

I tired the LED in both polarity configurations and with and without the resistor and couldn't get it to light - but it didn't smoke either. I thought that maybe the headlight pins were burnt out the decoder itself, but since the reverse lights work, I attached the LED to the reverse pins and also could not get any light from two different LED's.

Then I noticed in the manual for the decoder under step #9 of the decoder installation section:

_"This decoder is designed for use with 1.5V
lamps without the need for additional resistors.
Attach the wires for the lights to the decoder.
The headlight and backup light wires attach
to the two center tabs on each end of the
decoder. (2, 3, 10, and 11)."_

The LED's documentation state:

_"White LED specifications
3.2-3.6 Volts 20 milliamps Max
Use 1k ohm 1/2 Watt Resistors for 0-21 Volts"_

OK, so no problem, I guess I just bought the wrong LED's - but after looking and looking, I can't find any 1.5 Volt LED's in the 1.8MM size - Come to think of it, I didn't see any 1.5V in any other size either.

What I do know is that hooked them up correctly and can't get them to light or smoke - it seems that they're not getting the power they need to do either - any ideas anyone? I'm about to just buy some standard incandescent "Grain of Wheat" bulbs and be done with it - I just figured that since I have to replace them anyway, I might as well do LED's.


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## mopac (Feb 24, 2011)

No, you didn't buy wrong LEDs. You have to use a resistor. I looked at the decoder manual and 12 to 16 volts are coming from your light solder points. Those 2 LEDs
you tried I am sure are fried. I have blown many and never had smoke. Get you
2 more of the same LEDs and 1 resistor per LED. Try 680 resistance. Instructions
say you need resistors for 1.5 volt bulbs also. It does say no resistor needed, but
that is with 12 to 16 volt bulbs.


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## Cycleops (Dec 6, 2014)

Some decoders do have resistors already installed but in most cases you'll need them. Have a look at some of the vids on YouTube to get some tips on installing and identifying the polarity.


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## mopac (Feb 24, 2011)

It will not burn out LED if you get the polarity wrong using a resistor.
It just won't light. Reverse the wires if it doesn't light. If you touch
wires to 12 to 16 volts without resistor they will blow so fast and you
will not know. No flicker, no nothing. First time I bought LEDs I didn't
know about resistors and I blew them as fast as I could hook them up.
You will be fine, just use resistors and you will not blow them. I added 
the TSU 1000 to an athearn bluebox, used resistors, my LEDs work fine.
Some people have a preference on which leg of the LED to put the resistor
but I don't think it really matters. Either will work. Good luck.


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## SSBN743 (Dec 30, 2013)

OK, I'll give that a shot - I bought a whole bunch of them.

I'm still wondering why the manual says 1.5V with no resistor though...more to come,

Thanks,

Josh


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## DonR (Oct 18, 2012)

Before you connect anything get your multi meter and see
what voltage is actually fed by the decoder. That will determine
your next step. Check both front and back light terminals. If
there is a resistor in each circuit you should be able to see it. It
may be possible to by pass it and use the usual 12 V DC with a
resistor as has been suggested.

If you have an old Power pack with variable track DC you could
test the LEDs. Connect the long LED wire to + the short wire to -
and very slowly increase the voltage. When it gets to 3 or so volts
they should light. If not, reverse the polarity and try again. If
still no light, they are DRT...dead right there.

Don


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## SSBN743 (Dec 30, 2013)

Ok everyone – I finally got a chance to try these suggestions; here’s what I found:

1. The forward headlight ports on the decoder output 1.5V DC

2. The rear headlight ports on the decoder output 1.44V DC (I suspect that has something to do with the working load on those ports as to why it’s not exactly 1.5V)

3. There do appear to be resistors embedded in the decoder, however, they are all under the headlight and forward motor contacts – there are no resistors anywhere else on the board. I suspect that the PCB takes care of the details

4. I connected the two LED’s I originally connected to the decoder to a spare analog power supply; one with a resistor attached and one without. I am able to get both LED’s to light using the throttle on the power pack – the one with the resistor takes slightly more voltage to light – though not much more to be honest

Conclusions:

It appears that the manual is correct and I need a 1.5V lamp connected to the decoder - the resistor part is still up in the air, but it’d be a fairly educated guess to say a resistor is not needed.

I really think it is more trouble than it’s worth to attempt to build a voltage multiplier. Plus, I only know how to build double and triple multipliers, but in this case I would need an output factor of 2.15X -2.25X; which I don’t even know how to do; different value diodes? I don’t know – I suppose the Google machine could help with that, but…

The decoder has not produced enough power to smoke or light the two LED’s – since I don’t want to go through the trouble of building some sort of voltage multiplier, and I can’t find any 1.5V LED’s – it appears as though I must use incandescent bulbs with this Soundtraxx decoder.

Unless anyone else has a better idea?


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## johnfl68 (Feb 1, 2015)

Ok - you have an pseudo custom board that drops in for Athearns, I should have caught that.

I vaguely remembered something about this, and had to do some searching.

There is a 14V pad on the board that you have to use as an alternate, with the resistors for that voltage.

Look at this:
http://www.ulrichmodels.com/prostores/Soundtraxx/Soundtraxx_GN_Board.pdf


And also this for some extra guidance just in case, you may need to remap some of the CV's to get better prototypical lighting based on your needs:
http://atlasrescueforum.proboards.com/thread/2035/tsu-gn1000-issues-leds

Hope this helps!

John

More info:

There seems to be conflicting information as to if the GN1000 boards will do this in the long thread. Possibly some newer boards work, and some older ones don't?
Perhaps contact Tsunami Support about the issue, usually they are very helpful.

John


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## SSBN743 (Dec 30, 2013)

Wow - I'll bet that does the trick - seems like Soundtraxx should mention that in their documentation.

But that looks like the exact problem I'm having - and I have the +14 volt lead on the board.

I'll get on that - thanks for finding that for me!

Josh


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## mopac (Feb 24, 2011)

There must be 2 different GN1000 boards. I guess your instruction sheet is
correct about no resistors needed since you measured the light leads on the
board and they were around 1.5 volts. I looked at the GN1000 manual online
at Soundtraxx site and it clearly says light leads are 14 volts and 1.5 volt bulbs
and LEDs will need resistors. Well so much for adding LEDs, guess you have to
get some 1.5 volt bulbs.


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## SSBN743 (Dec 30, 2013)

johnfl68 said:


> Ok - you have an pseudo custom board that drops in for Athearns, I should have caught that.
> 
> I vaguely remembered something about this, and had to do some searching.
> 
> ...


OK, I finally got around to trying this and it does work - sort of.

Using the 14V common port, the two negative F0 positions, and attached resistors I can get the headlight to function and be directional (i.e turn off when in reverse). However, the rear light will not function at all.

I've read though some posts on the Internet and found that many have had issues with this; I couldn't find anything like what I am seeing though. I know both LED's are good and I wired them exactly like the below posts states, but still can't get the F0(r) LED to light.

http://www.ulrichmodels.com/prostores/Soundtraxx/Soundtraxx_GN_Board.pdf

I am about ready to try and run the rear LED to the extra FX function I have available, but I don't really like that answer since the light won't be directional and will have to be controlled manually. Does anyone have anything here?


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## Cycleops (Dec 6, 2014)

Check if you've got an output from the yellow lead and blue common lead. It's possible you've blown the output for the backup LED. Maybe return it to Soundtraxx for a fix. Might be an idea to email them with your problem, they will certainly be able to offer advice and a solution.
I have found on some decoders, but not Soundtraxx, the wires can come loose from the board through handling. Might be worth checking.


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## SSBN743 (Dec 30, 2013)

Cycleops said:


> Check if you've got an output from the yellow lead and blue common lead. It's possible you've blown the output for the backup LED. Maybe return it to Soundtraxx for a fix. Might be an idea to email them with your problem, they will certainly be able to offer advice and a solution.
> I have found on some decoders, but not Soundtraxx, the wires can come loose from the board through handling. Might be worth checking.


Well, could be I guess, but I actually did this on a brand new decoder (the first decoder had an unfortunate run-in with the soldering gun - an even though it still works, I wanted a new one to be sure. I accidentally removed one of the PCB resistors and when I tried to solder it back the decoder shorts out. I don't know, but it's probably a multi-layered PCB, which means, new decoder).

Plus, I've got something very peculiar going on, and it is exactly the same on both decoders regardless of the removed resistor on the old one. I wired the rear LED in FX6 and left the front LED on the F0(f) function. Now, the FX6 LED will light, and turn on and off with the function, but the F0(f) LED doesn't work at all.

It's almost like it can't handle 2 LED's, though I have no idea how it determines which one it will power. I did find a post on the Internet that suggests modifying CV's 59 and 60 on SoundTraxx because those CV's allow 14V LED's apparently. I haven't got to that yet, but that's my next step. After that, I thought of hooking 2 LED's into the same output, and seeing if both light.

Boy I tell you, nothing but problems with the Soundtraxx stuff; don't even get me started on speed matching two loco's - that is next to impossible with Soundtraxx.


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## Cycleops (Dec 6, 2014)

That is very strange, the F6 business. I think it may be time to call it a day and return it to Soundtraxx for a fix or initially mail them as I suggested. I have several Tsunamis and never had a problem. I've used LEDs with all of mine without having to change anything. 
Have you checked the rear light output with a multimeter?
As for speed matching you'll have that with any decoder.


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## DonR (Oct 18, 2012)

Sometimes a decoder that 'acts up' can be corrected by
setting it back to factory default, address 3.

Don


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## Cycleops (Dec 6, 2014)

Yes, that may be a good idea Don. With the Tsunami its CV 8 to 8 to reset it:

CV 8 Manufacturer ID
Description
Contains the NMRA issued Manufacturer ID code assignment for SoundTraxx/Throttle Up! (141):
Bit 7
Bit 0
1
0
0
0
1
1
0
1

Writing a value of 8 to this CV will reset all CVs to their default value. All other write operations will be ignored.


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## SSBN743 (Dec 30, 2013)

DonR said:


> Sometimes a decoder that 'acts up' can be corrected by
> setting it back to factory default, address 3.
> 
> Don


Yeah, I've done that - matter of fact, the new decoder I didn't modify at all; and just to be sure, I did write 8 to 8 and reset - same thing.

One question - I'm not quite sure how to illustrate this, but here's how I wired it:

F0(f) - >>>>>>>>>> Resistor >>> Cathode LED1
F0(f) + - blank 
14V Common <<<<<<<<<<<<<<<Anode

F0(r) - >>>>>>>>>> Resistor >>> Cathode LED2
F0(r) + - blank 
14V Common <<<<<<<<<<<<<<<<Anode

Do I need to reverse LED2, maybe? Or maybe reverse the Anode and Cathode?
F0(r) - - blank 
F0(r) + >>> Resistor >>> Cathode LED2
14V common <<<<<<<<<Anode

Also, I wired the FX function is like this:

F0(f) - LED Cathode >>> Resistor >>> Cathode LED1
F0(f) + - blank 
14V Common <<<<<<<<<<<<<<<Anode

FX6 - LED Cathode >>> Resistor >>> Cathode LED2
FX6 + - blank 
14V Common <<<<<<<<<<<<<<<<Anode

In this configuration, only LED2 lights - figure that out? It does it on both decoders too, that's why I'm thinking I need to reverse LED2, but that's really kind of a guess. From how I read the "ulrichmodels.com" diagram, I did it right.


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