Convert my MTH Dash-8 to DCC

Well, since you don't have the switch, you'll have to pop the top.  There should be a loop of black wire between two contacts at one end of the  40-pin connector, those are the switch wires.  In many of them, the loop is long enough to cut, install the switch, and have it switchable.  If you want just DCC all the time, just cut and insulate the ends of the wires, Job done.

Thanks, my question was more towards how to get the cab off. I figured it out while listening to a bunch of executives argue about program costs on a work call just now. The wire I see and will take care of. Wasn't as hard as I thought it would be.

They should have left the switch in. Stupid cost reductions...

Thanks though, I appreciate the help.

Drop a switch in, then you won't have to do it again.

I should have. I got it taken apart, cut the black wire, and put it on the track. Address 3, it starts up, a bit of lights, smoke stack works, start to move it forward, then a nice bzzzztttt sound while the lights flicker, and then it's dead. Likely, completely dead now. I get no response to any command on address 3. Is there something I should look for? I don't see any broken wires, don't smell or see any electrical damage on the logic board. What might I have done?

Pretty hard to say, look for any pinched or broken wires, that's the usual cause when things go south after opening one up.

Just curious but did you insulate the wire ends like GRJ instructed?

Is this a Premier locomotive? I didn’t know MTH took the switch out at some point.

I wrapped them, but did not insulate. Railking, their Christmas Dash-8. I didn't get the entire thing back together, and left a few screws out to make sure it worked first. It's entirely possible the black wire shorted. I would guess it's attached to a GPIO on the micro on one end, and the micro voltage on the other end. It probably checks for high/low to see which state it's in. If I did short it, I'm not sure what damage that could have caused, but it's possible. Pretty freak if the ends of that wire contacted the wrong thing as they weren't exposed and were tucked into the wire bundle over the logic board, not really exposed.

Where can I send this for repair? Getting late to make Christmas though, which is a bit upsetting to me. I had such good luck with my other MTH engine.

Sorry to hear that Pete. It was my understanding that Railking locomotives do not get the switch only Premier locomotives got it and that would explain why yours didn’t have the switch. I could be wrong though. Just a guess but it sounds like those wires didn’t cause the problem. Perhaps it’s a pinched wire like John said.

As for getting it repaired we have some excellent repair guys on this forum like GRJ, Alex M., and GGG. I would take it to one of them if I could not figure it out myself. Good luck and keep us posted.

Me too, @gunrunnerjohn, I see your signature includes MTH service, can I send it to Henning's? I won't cry too much about how long it might take to get it back. Right now, it just is what it is.

I think I found the problem. I don't think it was the black wire, I think it was one of the LED strands for the Christmas lights. I didn't see it broke, and the wires are loose and bare, where the black wasn't. I guess that's probably on a switch of some sort, and may have shorted directly to the frame. The LED's were on, so I can see where the new voltage source may have caused everything to go south.

Is it easy to just replace the logic board? I'm looking at it right now, and it looks like the worst part is handling the mass of wires. The board itself is just a few screws and JST type connectors. Does MTH sell that as a replacement part?

I don't think MTH sells the bare board to consumers, and I'm pretty backed up right now.  I'd suggest GGG, he's an excellent MTH tech and I think he can turn it around faster than I can at this point.

Yeah, I was digging around their website and I don't think they do. Who is GGG, sorry, I don't recognize a name associated with those initials. I'd love to get it done if I can, but will survive if I have to let it go past the new year.

Also, does anyone have a Digikey part that would fit the switch location on the loco? I don't have anything similar in my box of old parts with the right screw hole placement, and I'd rather not guess.

Member GGG.  I'm surprised you haven't seen his postings, he's very active with MTH repairs.

The switch is a standard switch widely used by both MTH and Lionel for most of their selection switches.  I don't happen to have a Digikey part # simply because I've never had to buy these.  I have so many from conversions and upgrades that I just go to the parts box.

I can't find a match to the screw hole distance on Digikey, but I'm still searching. Will try Mouser next I suppose.

Thank you, I probably have, but it didn't click.

Send me an email and I can fix you up with a couple.

I think I found them on Digikey. The challenge is they are a standard but smaller than normal with a very small wattage rating. I'm going to get both and see if they fit (I have an open and unused chassis just sitting here to allow me to do that!). I'll update with some results once they arrive.

Thanks for the offer @gunrunnerjohn, but since MTH will stop making the engines, I need a plan in place to modify hundreds of engines that I will very specifically NEVER use because I am unlikely to buy new engines anytime for this small layout. Why not, right?

• https://www.digikey.com/en/pro...93?itemSeq=343252507
• https://www.digikey.com/en/pro...43?itemSeq=343253250

Well, they might fit, but since they're rated at 300ma, I have to wonder about the model train practice of passing track power to the engine through them, that can exceed several amps with any load and smoke running.  Of course, I don't actually know what the MTH switches are rated at, but 300ma seems low...

I would hope that track power isn't going through that line. It's like a 28 guage or smaller wire, and it's LONG. This likely must only be a signal wire on the micro which is just a check at startup specifying which state machine to enable (DCS or DCC). For something like that, 300ma would be about right, and I would guess actual is 20ma at 3.3 or 5 volts depending on micro operating voltage.

Well, that particular switch carries no significant power, I was simply thinking ahead to all the other switches used in these models.  You did mention hundreds...

AH, funny. Yeah, just that switch. I meant hundreds of new engines I will want to, but not actually will ever, buy. Each one would need a new DCC switch of course!

Regarding the elimination of the DCS/DCC selection switch I'd bet it wasn't a cost-reduction move. It was probably a customer complaint reduction move. I wonder how many people, unaware of DCC at all, accidentally flipped that switch and then called MTH or their LHS complaining about this hunk-of-junk that suddenly stopped running.

That seems more likely than cost reductions. I was doing some napkin math on the cost and margins for an engine like this, and I would bet they could source the switch for < .50, which at the volumes they do, doesn't seem like it would save very much money versus the anger generated by the handful of people like me, who end up bricking their new engine. Overall, pry savings < 10k for the entire line that would use those switches. I would love to know why exactly. Everything is there *except* the switch itself, so they didn't really design it out, they just removed it.

@geysergazer posted:

Regarding the elimination of the DCS/DCC selection switch I'd bet it wasn't a cost-reduction move. It was probably a customer complaint reduction move. I wonder how many people, unaware of DCC at all, accidentally flipped that switch and then called MTH or their LHS complaining about this hunk-of-junk that suddenly stopped running.

You're exactly right, and we received a Service Bulletin stating that exact fact.  Also, since it's till on Premier models, I've personally sent back at least half a dozen locomotives that were dropped off as non-functional after flipping the switch and reviving them.

@geysergazer posted:

Regarding the elimination of the DCS/DCC selection switch I'd bet it wasn't a cost-reduction move. It was probably a customer complaint reduction move. I wonder how many people, unaware of DCC at all, accidentally flipped that switch and then called MTH or their LHS complaining about this hunk-of-junk that suddenly stopped running.

Documentation about the missing switch from MTH does in fact say it's due to numerous calls from confused customers.  I suspect it's due to the typical buyers of Rail King vs Premier locomotives.  Rail King are generally not model railroaders, so they'd get mixed up with that switch.

Sad to hear about your issue.  I've opened and DCCed two of the RK -8's myself, but neither where Christmas ones.  Those middle tank screws got me both time, forgetting that they also hold the body on.  The outside end screws were easy to figure out they held the body on.  But getting them back together was a hassle both times, amazing how much they shove in these bodies.

@gunrunnerjohn posted:

You're exactly right, and we received a Service Bulletin stating that exact fact.  Also, since it's till on Premier models, I've personally sent back at least half a dozen locomotives that were dropped off as non-functional after flipping the switch and reviving them.

I couldn't count the number of service calls I went out on where the repair consisted of flipping the circuit breaker(s) back on. And some where what I did was either plug the thing in or turn on the water. We humans iz easily forgetful.

Wow, thanks to all on the details. That's cool history/new data. I appreciate it.

Because it's almost Christmas, and the layout was built for this specifically, I just got a second one (wife does not know yet, please keep this quiet). That conversion went flawlessly, and the new loco runs as expected. I plan to fixup the other one eventually, and when (if?) I expand the layout, maybe consist them, which might be kind of cool actually.