I gotta quit smoking... decoders, that is...

[C855B]

Besides, they don't roll very well in the cigarette papers.

Last night I blew-up the third decoder in an Arnold U28C in as many weeks. This one was particularly dramatic, with lots of light gray smoke pouring out of the back of the engine. Sorry I didn't capture it with a phone vid. It was fun. With heating season about over and the furnace not running much, that wonderful... aargh!... aroma will hang around the train room for a day or two or three. I could claim I was accurately modeling a typical GE, but, no, that's not right, the unintended smoke on the 1:1 emanates from the middle of the carbody.

The Arnold U25C/U28C models take the normally butt-simple 6-pin "EUN"-type decoder. Plug and play, supposedly. The problem is the location of the 6-pin socket, which is perilously close to the rear truck pickup spring tabs.

First one to die this particularly ignominious death was a TCS EUN651, which are mighty expensive ($50) these days for a non-sound decoder. Passed the bare chassis test with flying colors, programmed up just fine, put the body back on, put it on the running rails, and then... "what's that smell?" By the time you get the smell, you know it's too late. In this case, the pins on the TCS decoder are too long. In putting the shell back on, the decoder was pushed deeper into the open-ended socket, and one of the pins made contact with a pickup tab. Poof.

Second try was an ESU LokPilot 5. In the version with integrated plug, they come with five wires for AUX functions that have to be trimmed off if you intend to use it as a bare 6-pin decoder. Learning my lesson from the long pins on the TCS, I also trimmed the pins to be sure there was no risk of accidental contact through the socket. It also worked fine test-running the bare chassis. Put the shell back on, and it ran for a couple of feet and just stopped. No smoke, no smell, but it was clear at that point it was tits-up. I was thinking for a moment that the AUX wire trim (tiny wires) inadvertently left some strands touching, but no matter. Two down.

Last night's third try was with another ESU. Trimmed everything very neatly, plugged it in, test run with the bare chassis on address 3 was perfect - these are very smooth runners, always impressive - touched-up some programming, ran fine with the reassigned road number. Everything is great.

So, after a half-hour of enlarging coupler pockets (slightly small for the 1015-sized TSC box), shell goes on and it's put on the rails. Lights come on, so far so good, apply throttle. Hmm. Sluggish. Did I kink something with the shell? Is something binding? Reverse it back and forth a few times, still sluggish. Take it off the track, put it back on, and that's when things went decidedly south. Like I said, smoke pouring out of the back of the loco.

Back on the bench I open it up to find that the decoder is a wad of goo, the shrink-wrap having melted, leaving scorch stains on the motherboard. No apparent damage to the shell other than deforming the ladder over the radiator (a detail which wasn't exactly right anyway). Decoder welded itself to the motherboard socket, and burn marks on the truck pickup tabs.

Is it recoverable? In my assessment, yes - remove the now-unusable socket from the motherboard and hardwire. I'll do an add-on to the order already in the works with my fave model supplier for a six-pin-with-wires ESU LokPilot.

I have too much invested in this one model to give up on it. Would I replace it if I can't make it work? No, they're commanding top-dollar on eBay. It can certainly become a dummy, and since I have two other Arnold U-boats that are running just fine, the internal running parts go into the fix-it parts bin.

[JeffB]

Your experience here is the main reason I shy away from adding DCC sound to a locomotive...

The possibility of "smoking" a $85-$125 motor/sound decoder just puts me off wanting to even try.

Don't relish smoking a $30 +/- motor decoder, but that's a lot easier to stomach than the more expensive motor/sound version.

Good luck with attempt #4...  Hopefully you don't repeat past experiences.

JB

[peteski]

Mike, if I understand it correctly, you have 3 identical models, and only one smokes the decoders?  I wouldn't think it should be difficult to figure out what's the problem.

You mention proximity to the truck pickups.  If the ESU decoder had shrink sleeve on it, how would it short out to the pickups?  Did you jam the shell on, causing the decoder to push against the pickups, puncturing the plastic sleeve?  Any chance of doing a postmortem?

Jeff, I wouldn't sweat this. We on TRW install lots  of decoders, and they survive. Some even do it as a job.  Even Mike himself is a successful decoder installer (sans this episode). Maybe he just needed to vent.  I'm also surprised he allowed 3 decoders to smoke.  I would hope that if this was me, I would have stopped at 2    and got to the bottom of the problem before installing a third one.  But then again, talk is cheap. 

[C855B]

Two if not three different problems, Pete, although at the time I chalked-up the second one to possibly a defective decoder. I plugged-in a known working TCS EUN651 earmarked for another project and it ran fine, but... again... without the shell.

Any carelessness on my part on the third was not double-checking that the truck pickup tab didn't skew during shell assembly, which would (potentially) have pushed it into the base of the connector. The tabs can skew since they're separate for each truck and fastened to the motherboard with a single rivet (i.e., rotation point). No possible way the plastic shield would have been compromised, as it is quite thick. However, and tempting fate, I will go back to the other two and wrap some kapton tape around the bottom of the connector should truck movement pressing against the tab release this particular gremlin.

Bottom line is a design with a vulnerability around the decoder socket. As far as Jeff's concerns go, I just add the "...oops..." potential in general to the 20+ reasons I don't do sound. Smoked decoders may not be common, but they do happen, even to the long-experienced. 

[peteski]

Sorry Mike if I did not understand. I thought you blew up 3 decoders in the same loco, but it now sounds like it was 3 individual locos, one blown decoder in each? Sorry if I sound dense, but I just didn't understand.

If the plastic sleeve is  not damaged, I wonder why those decoders smoke when the shell is installed?  Or do you know that the truck contacts were the culprit?
Borrowing image from Mark.


It is a single PC board with the decoder installed under it.  No wires to get pinched. Other than those riveted contacts, there doesn't seem to be any other possible chance for shorts.  But I do agree that the way those contacts are designed is rather awkward.

[tehachapifan]

Don't have one of these locos, but those riveted contacts, if I'm looking at the right things in the pic, look spooky to me. Could the shell press down the board and make those contact the frame?

[C855B]

Here's the problem area:

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Notice the very small gap between the decoder connector and pickup tab. This happens on both sides, obviously. IF the tab gets slightly squashed or otherwise deformed, it can contact the exposed pins from the socket to the board. Also... that I'm noticing from this picture, especially, I may very well have contributed to the failure conditions by trimming off the unneeded AUX wires, exposing the trimmed end of three of them to the tab IF the socket droops to where they contact the tab. The socket was in fact drooping due to multiple plug/unplug operations trying to get this all straightened out. In this realization I think I can leave the other two U-boats alone because if they haven't failed by now, they're unlikely to. Hard-wiring the third eliminates the socket, so problem solved there.

The frame has no electrical contribution. The truck contacts reach up to the tabs on the motherboard, a lot like what Kato does with their passenger car lighting system.

[C855B]

Hey, Pete - if you want to move this to DCC/Electronics, be my guest. I primarily posted it in Crew Lounge because of the story of the travails, not the tech interest.

[peteski]

So theoretically sticking some Kapton tape on the side of those springy contacts which is facing the decoder and the 6-pin connector should prevent any problems.  Or adding some Kapton tape over the connector and decoder should do the same.

Another unrelated thing that worries me a bit about these models is the plastic gears on the axles. I hope they won't be prone to cracking with age.

[JeffB]

Jeff, I wouldn't sweat this. We on TRW install lots  of decoders, and they survive. Some even do it as a job.  Even Mike himself is a successful decoder installer (sans this episode). Maybe he just needed to vent.  I'm also surprised he allowed 3 decoders to smoke.  I would hope that if this was me, I would have stopped at 2    and got to the bottom of the problem before installing a third one.  But then again, talk is cheap. 

I've done decoder installs...  Several, but all motor only.  My fav at the moment is the ESU Micro decoders. 

But they're about $30-$35, which is easier to stomach should I bonehead an install and smoke one.  But I have, though not since the days of using the old Digitrax DZ123 low end decoders (which were even cheaper). 

I have gotten better with my installs (finally got around to buying the correct size shrink tubing for the tiny wires) and haven't smoked one in a while. 

So maybe I can/should brave a sound install... 

Jeff

[wvgca]

sure ... try a sound install .. i have done maybe fifty decoder install [mostly steam locos], but all HO and maybe a quarter were sound  ..
i have never done an ESU decoder or a N scale,
this is an image of a home made decoder [pcb was ordered in] copying most of a merg decoder with updated components
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[peteski]

I've done decoder installs...  Several, but all motor only.  My fav at the moment is the ESU Micro decoders. 

But they're about $30-$35, which is easier to stomach should I bonehead an install and smoke one.  But I have, though not since the days of using the old Digitrax DZ123 low end decoders (which were even cheaper). 

I have gotten better with my installs (finally got around to buying the correct size shrink tubing for the tiny wires) and haven't smoked one in a while. 

So maybe I can/should brave a sound install... 

Jeff

LOL Jeff!   The only difference between sound and non-sound are 2 extra wires for the speaker.  Everything else is identical.  Of course if you start adding extra capacitors or a real keep-alive module, then it would be 4 or 5 extra wires beyind a non-sound decoder install.

Both sound and non-sound decoders are just PC boards with components on them, covered with a heat-shrink sleeve (or bare boards if using Next18 interface).

Yes, I realize that the there is a cost difference, but the chances of blowing up a sound-decoder are similar to non-sound decoders.  Either way it bays to be a fastidious and careful installer.  Even if you screw up, manufacturers will repair or exchange the decoder usually for less than original cost.

[JeffB]

LOL Jeff!   The only difference between sound and non-sound are 2 extra wires for the speaker.  Everything else is identical.  Of course if you start adding extra capacitors or a real keep-alive module, then it would be 4 or 5 extra wires beyind a non-sound decoder install.

Both sound and non-sound decoders are just PC boards with components on them, covered with a heat-shrink sleeve (or bare boards if using Next18 interface).

Yes, I realize that the there is a cost difference, but the chances of blowing up a sound-decoder are similar to non-sound decoders.  Either way it bays to be a fastidious and careful installer.  Even if you screw up, manufacturers will repair or exchange the decoder usually for less than original cost.

Got it...  Unnecessarily worried and paranoid.  I guess I should just bite the bullet and buy my first sound decoder. 

May or man not do a keep alive.  The custom mechanisms I build are equalized, so as long as the track is not absolutely filthy, they should be OK without it.

Jeff

[peteski]

Got it...  Unnecessarily worried and paranoid.  I guess I should just bite the bullet and buy my first sound decoder. 

May or man not do a keep alive.  The custom mechanisms I build are equalized, so as long as the track is not absolutely filthy, they should be OK without it.

Jeff

Do it!

And the "real" keep alives are more for things like longer duration intermittent track contact while going through complex trackwork like turnouts then just for those microsecond dropouts caused by dirty track or wheels.  I also suspect that there are more sound decoders out in the wild without any additional capacitors (other than what is already on the decoder) than ones with modeler-added capacitors..

[Ed Kapuscinski]

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