Burned "run" on MTH RealTrax Switch

I burned a “run” off an MTH RealTrax Switch, probably during a derailment.   Two questions come up.

 Is there any repair remedy for this problem other than replacing the Switch?

IMG_0781.croppedHow can I prevent this in the future?

 I am using an MRC Dual Power Transformer to MTH TIU to two loops of combination Lionel O27 tubular track with adapters to MTH RealTrax. Each loop has 6 blocks with 4 switches providing crossovers between the loops.

The wiring is fairly standard, MRC Transformer to TIU is protected by two 10A Fastblo fuses. The outut of the TIU is connected to 12 block relays controlled by Outside rail Isolated Track Switches. The output of the relays fan out via terminal blocks to each block.  MTH Switch Power is 14vac from the MRC Transformer.  I have not blown any fuses in the TIU or the 10A Fastblos and have had no Circuit Breakers open on the MRC Transformer during the time span in question.

 As I hope you can see, it was the center rail that overloaded. It seems I don’t really have any overcurrent protection if this can happen. 

Suggestions appreciated,  Dick

Dick Autz

Hagerstown Model Railroad Museum, Inc. @ Antietam Station

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Solder in a wire...if it will clear things. I have to assume it uses a board because of a clearance issue? Running it outside the switch is unsightly but effective

Or maybe solder in a thin flat strip of copper or brass for modeling . That would increase the amp capabilities. Adding fusing/breakers would protect those traces. MTH would know the max amps it can pass, fuse the switch(or track) lower than that max.

Ribbon wire?

I've always heard it called a "trace" for board work fyi. There are trace repair "kits" and "fluids/compounds", but they really aren't worth a crap. The get-r-done or board swap approaches are best for traces imo. 

"Still trying to not shoot my eye out"

 

"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.

 





You more or less have 10amps constant draw of protection. Going to 10a fast blow, and or an 8a s.b. would be a good move. In fact, keep dropping the value till you DO blow a fuse, then raise the value by ½-2amp; "depending". As low as possible protects best, fast blow protects best. Slow blow should be saved for "fine tuning" systems. 

You shouldn't really count on switches to pass power to connecting rails. Even Lionel always suggested a power drop be run to all three sections of connecting rails; three lock-ons per switch. A drop to all three connecting sections of track should prevent this excepting maybe a fluke oddball derailment on the switch being ignored. The three drops give a heavy draw a path other than that trace. (I think it may also make the repair unnecessary )

"Still trying to not shoot my eye out"

 

"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.

 





It's the red wire that carries the power through the rails.  If a short occurs on a portion of the layout on the other side of where a lock-on is attached, the short passes through the small ribbon trace and burns it up.  MTH sells that PCB; I have replaced lots of them.  The thing to look for is warping of the plastic under the points. This can inhibit movement, but sometimes can be clearanced with a dremel.  Placing a wire next to to the PCB may inhibit movement of the white plastic part of the mechanism.  A quick fix is to leave that PCB in place and just solder the short straight center rail between the points to the wide center rail as this will effectively jumper the red wire on the PCB.

Jon G TCA 95-41020

Independent Lionel Service Tech

MTH Service Technician at MTH

Jon G posted:

 

….  Placing a wire next to to the PCB may inhibit movement of the white plastic part of the mechanism..

Picture worth a thousand words...

IMG_4105

Looks like zero vertical clearance above the surface of the board.  I wonder the cost (with shipping) of a replacement board which is arguably nothing more than a 4-wire extension cord (no electronics).  Considering the effort to de-tach then re-attach the 8 wires, perhaps it would be possible to gouge out a ditch in the existing board where the red trace burned off and lay down a piece of wire which would be flush with the board surface. 

IMG_4106

The ditch would not need to be the entire length of the board since the white plastic piece only slides over about half.  The wire could be soldered to the existing solder blobs for red.

 

 

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stan2004 posted:
Jon G posted:

 

….  Placing a wire next to to the PCB may inhibit movement of the white plastic part of the mechanism..

Picture worth a thousand words...

IMG_4105

Looks like zero vertical clearance above the surface of the board.  I wonder the cost (with shipping) of a replacement board which is arguably nothing more than a 4-wire extension cord (no electronics).  Considering the effort to de-tach then re-attach the 8 wires, perhaps it would be possible to gouge out a ditch in the existing board where the red trace burned off and lay down a piece of wire which would be flush with the board surface. 

IMG_4106

The ditch would not need to be the entire length of the board since the white plastic piece only slides over about half.  The wire could be soldered to the existing solder blobs for red.

 

 

Could you use a very thin strip of brass or copper where the burnt trace is or route it the way GRJ suggested?

Steve

I really appreciate the suggestions.  I think replacing the "trace" (Thanks Adriatic) with foil or copper is probably beyond my level of dexterity. However Gunrunnerjohn made me think about how I could run the red wire but not under the switch parts and if I can clean up the burned area I may be able to run a wire outside the switch from the third rail over to the screw terminal on the side of the switch.  A much less elegant patch I'll admit.  JonG you mentioned replacing the pcb and I was wondering what that might cost, part# to order, etc.   I liked Stan2004's close up of the assembled switch, it shows that for the switch to work right, I will have to be very careful.  Adriatic you mentioned changing the fuse values so that this condition would blow a fuse before the trace would burn.  Do you happen to know about fast acting circuit breakers that I could install on each block to protect the switches?

Again many thanks for the help.

Dick Autz

Hagerstown Model Railroad Museum, Inc. @ Antietam Station

If you replace the fuse with a wire, you won't have to worry about the trace anymore.

The groove where the cooked trace is would be easy, warm up the Dremel tool.   Then you could just lay a wire in the trench, and it could even be a bare wire.

If you replace the fuse with a wire, you won't have to worry about the trace anymore.   Good One.

Years ago I was known to put a penny under a round panel fuse if I didn't have a new one.  It eventually came back to bite me.

I have got my switch working again.  A little elbow grease and 600 git paper cleaned up the damage to the plastic switch parts and then a little silicon spray.  I replaced the red wire and ran it outside the switch back cover and then in again in an access hole, then connected it to the Track Power screw terminal buss bar inside the switch.  Using 22ga wire it doesn't leave much a bump on the bottom of the switch.

Now I need to find a way to protect my other switches.

Thanks, you are a great bunch of guys.

Dick Autz

Hagerstown Model Railroad Museum, Inc. @ Antietam Station

Is that a size match to the red wire? (Or larger is ok too)

22g seems light and may get hot. (I associate 22gwith about 5a continual draw, 7a surge max, but the shortness might really increase that max?? [ I'm not prepared for that "short wire" math, lol]  I'd run a second wire if it is smaller than the red wire otherwise you have the same basic issue.

 Just because your transformer puts out 10a doesntd meant you want 10a fuses. If the wire (or track) only handles 8amp cont., you fuse at 8amp. Fuses/breakers should guard weak points. A line should be fused right? (Right). Adding lighter wire to that line(now a bus)  fo an accessory? Ideally a new fuse should be added at that draw point(block)(right) This switch is passing 100% of the used track power unless your blocks and feeds are set up with alternate power paths around the  switch (drops/jumps/feed/lock ons) Your block set up if butting to the turnouts may complicate things there. " Blocks can be set up in many ways.

  This turnout's board(s) is(are) your layout's weakest link(s) as is IMO. And as is, the feed to the track must be fused below this/these traces(wire) maximums to protect the traces from 10a. I'd bet 6-8a is the max on the trace; if that. Your wire? 5a imo. 

OR make sure there are drops/feeds to each track piece that attaches to all three legs of the turnouts. Even a jumper wire ( vs a bus feed) between these 3 tracks will keep a heavy draw off those boards.

So, adding breakers just to guard those tràces and allow 10a to the track isnt really feasible outside of fusing the switch's blocks lower than other blocks; kinda silly to bother trying to feed in 10a over there if 6-8a is enough over here.

Lower your main fuse/breaker rating and or add the 3way bypasses imo. (I like to tune in circuits with fuses, then choose a breaker based on that )

"Still trying to not shoot my eye out"

 

"Nursing insomnia one railcar at a time"

My aroma therapy? Smoke Pellets.

 





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