Stock Board LED Illuminating When Other Outputs Activated

[tehachapifan]

Now that I have my Locomotion CV's operating correctly when in consist, I want to once again try to tackle a lighting issue I've been having ever since I installed the Digitrax DN163A3 for the Atlas MP15DC. The board has 4 extra output pads and I am currently using 3 of them for lighting using SMD LED's with resistors. For some reason, activating any one of these outputs also causes the stock front headlight LED on the board to illuminate. Two of the outputs are used for front and rear headlights and activating either one of these causes this board LED to also light (they currently operate with FO/R as well as with F1 & F3. If I activate output 4 by itself, which is set to gyralight, this stock board LED also displays the effect but returns to steady on if any of the other lights are activated. I've tried every CV adjustment or change I can think of to disable the board LED but to no avail. I wouldn't normally care except I believe the stock LED may possibly be robbing output power to my added lighting as they are not displaying quite as bright as my other locos. I'm curious if anyone has managed to add lighting to the output pads on this decoder but has not had the front stock board LED also illuminate when they're activated, or have noticed similar behavior on this or other decoders.

[peteski]

The hardwired on-board headlight lLEDs will nto rob the other functions' power output. LEDs use way less than each output's maximum rated current (so the total current is also way lower than allowed).

Can you either take a photo or draw a diagram of how exactly you hooked up the extra LEDs?  Does the decoder you are using have the current limiting resistors already built-in into the decoder for the F1, F2 and F3 outputs?  If you then added another resistor outside of the decoder then they will glow dimmer.

As far as disabling the built-in F0F and F0R, I think that this decoder is capable of function remapping, but it is a pain to figure it out.

[tehachapifan]

Here's a pic of the install (Edit-This hookup is incorrect). The decoder appears to have a bunch of solder pads but only the first 2 on each side are indicated in the manual as being function pads. The common pad is not clearly marked in the manual but I had heard that the one behind the front LED is the common. All the lights work, albeit a bit dimmer than on my other DCC locos, so I'm assuming this hookup is correct. I'm not spotting any obvious on-board resistors for these outputs, but...



I should clarify that the lights are illuminating well, they are just not strikingly bright like on my other DCC locos with added lights (same LED's and resistors). The output powers are also listed as being the same on at least one of the other decoders from a different mfr.

I have also contacted Digitrax Support and made the same inquiry.

[peteski]

Russ,
I looked around Digitrax website and I also couldn't find any details on the extra function pads on this particular decoder.  There are knowledge-base articles showing the pad layout on several other flavors of DN163, but not on this one.  They should really create an article specific to this decoder. Actually, I think that this info should be presented on the installation manual which is included with the decoder. 

The closest article I found was this one: http://www.digitrax.com/tsd/KB5/dn163a1-function-outputs/  The layout of the ends of that decoder is very similar to yours.

I also think that I found what the problem is. Judging by the description of your problem and looking at the layout of the DN163A1 I'm pretty sure that you hooked up the positive LED leads to the wrong pad. The common positive pad is on the the other side of the decoder (as marked in the photo in the above article).  Try that pad and see if it works better.

[tehachapifan]

Thanks, Peteski! I had considered the possibility of that pad behind the rear LED possibly being the correct common, but the info I had rec'd before specifically mentioned the pad behind the "front" LED. That said, the decoder you found looks almost identical, except that the pad-heavy side of the DN163A3 goes towards the front of the loco but goes towards the rear on the DN163A1. I'm willing to bet you are correct but I'm going to wait to hear back from Digitrax to confirm before I attempt anything and risk liberating the magic smoke.

[peteski]

Thanks, Peteski! I had considered the possibility of that pad behind the rear LED possibly being the correct common, but the info I had rec'd before specifically mentioned the pad behind the "front" LED. That said, the decoder you found looks almost identical, except that the pad-heavy side of the DN163A3 goes towards the front of the loco but goes towards the rear on the DN163A1. I'm willing to bet you are correct but I'm going to wait to hear back from Digitrax to confirm before I attempt anything and risk liberating the magic smoke.

I don't blame you for waiting. But I'm pretty sure that this is the problem.  Since you are in contact with Digitrax, ask them to create a knowledge-base article on this decoder, similar to the one I found on the other decoder. That way this info will be available to everybody without needing to open a support case with Digitrax.

The way I see it (and the symptoms confirm) is that the pad you are using for a common positive is actually the cathode of the front LED.  When you turn on any of the extra LEDs you are using, the circuit to the positive is completed through the front LED and its 750 ohm resistor (onboard).  Since you now have 2 LEDs in series with 2 resistors, they glow much dimmer.

[tehachapifan]

I'm sure you're right. Now that we're going into the weekend and probably won't hear back until next week, I may just give it a try tomorrow and see what happens.

[tehachapifan]

Bingo! Couldn't wait and had to test it. You were right, Peteski, it was the pad behind the rear LED and the test LED lit much brighter off it. I'll re-solder the light leads tomorrow. Respect props added (not that you need it! )

[jagged ben]

Digitrax is such a...   Okay I'll try to keep my mouth shut.

I'll just say, they used to have an annotated photo of all the function pads in their instruction sheets.

[peteski]

Excellent Russ!  Thanks for the follow up.

Jagged ben, I'll say it:  Digitrax documentation stinks!  This an excellent example:  They sell this 6-function decoder without any means of identifying the extra functions. This info should really be in the installation guide which comes with the decoder.  Just a small diagram is all that is needed.  As we can see, Digitrax did eventually post that info in their knowledge-base for many of the DN163 decoders, but not all of them. WTF?  Plus, it is not easily found.  I would have posted a link to the appropriate articles about this extra functions right on the main page for each of the DN163 decoders. But no!  Instead, the customer is forced to sift through the knowledge-base and try to find it. 

I do like Digitrax decoders (well, except the way the handle LEDs for special effects), the prices are really good too, but everything else about them stinks. 

[tehachapifan]

Here's the unit all put back together and displaying much brighter lights ....



It was very tough getting all the wires tucked back in with the new common hookup being on the back of the board. With everything originally being (incorrectly) connected to the front of the board, I at least had nice, even LED leads that were able to loop back once above the chassis as per the above photo. Now it's a bit of a rat's nest, but it finally all fit in. If I was to start over from scratch, I would mount at least the front LEDs on the chassis like on my SD9 and my SW1500 bash as there's really not enough room above the chassis for the extra wire in these units needed with shell-mounted LEDs, especially in the area of the hood just before the cab. I'll do this on the SP MP15DC I'm working on.

[peteski]

Nice and bright Russ!