Dead FasTrack switch

Check out this recent thread for an extensive discussion of possible issues and solutions with an O72 FT switch.

Fastrack 072 switch problem | O Gauge Railroading On Line Forum (ogaugerr.com)

@CUPRI posted:

I have a dead LH O72 FasTrack switch.  No light and no action.  I suspect it may not be a simple repair, but a replacement circuit board is pretty expensive while a new voltage regulator, diode or transistor could be a cheap fix since  there appears to be no 5 VDC.  There should be 5 VDC on the terminals to the LED light stand, but there is not.  Nor is there 5 VDC on the output of the voltage regulator.  I am guessing there should be some higher DC voltage on the regulator input, but there is not.  There are no smoked components and nothing is hot under power.  Does anyone have a diagram for the circuit board showing AC and DC voltages?

No diagram directly for the main control board, however, the common failure is either the basic folded tab construction of the metal bus bar system, failure on the order of the contacts that have the ground, track , and aux power in, last it's possible to have a failure of the resistor they put in the power wire going to the board.

I would check the obvious stuff first- solder the tabs, check the order of the terminals vs the labels, ensure your power jumper is correct for using track power as the source- or even worse, definitely verify before connecting aux power it's actually going  into the switch logic VS shorting to GND or instead going up the fine wire to the track.

Also, this being an O72 switch- just saying last year, I ordered 9 new ones from a vendor and all 9 had wiring errors. The 4 more I bought recently had the same errors !!

I like these switches once you fix them- but that is key- once you do the full bulletproof mod and properly wire them in, they work great.

If you just take them and install them out of the box- or worse, just connect aux power thinking the connections are labeled correctly, then  failure is highly likely. 9 last year and 4 this year new in the box from vendors- the numbers are not on your side. 13 for 13 miswired from the factory.

Just a point of clarification. Yes, all 13 had a wire order or assembly error. That error specifically was that Aux power and Track were reversed compared to the outside labels stamped into the metal cover.

As delivered with the jumper installed, they would work out of the box on track power. However, if you then removed the jumper and wired to what you thought was Aux power, you would be shorting your Aux power into the track 3d rail, and no power to the switch.

Again, out of the box, a person could unwittingly test these switches with track power, even use them with track power and be completely unaware. However, later, when they attempted to use Aux power or had an issue using track power via the jumper due to folded tab contact failures in the switch, then that miswire or terminal order vs labels becomes a very big deal.

I just pulled the AC power lead out of the connector to the circuit board.  I get 4700 ohms for the series resistor.  Is this the correct value?  That seems like a very high value implying that only a few mA AC could flow into the switch!

The in line resistor (pseudo-fuse) covered in heat shrink tubing is supposed to be 2 Ohms 1/4 Watt.

https://ogrforum.com/...or-fastrack-resistor

Being bugged by the high resistance of 4700 ohms, I took apart a good switch and measured the series resistor in that switch and got only 2 ohms!  I then looked up the parts list from the Lionel web site and found they list a 2 ohm resistor part #cs-6102045603-p.  The parts list does not say nor show what the 2 ohm resistor is for, but I think my evidence is that they put too large a resistor in my bad switch!!!!

@CUPRI  I think our posts crossed.  Please see above.

Yep ... thanks for the confirmation!  I'll order the part from Lionel and hope that fixes it up.

@CUPRI If interested in getting it faster (maybe cheaper) you could also order a 2 Ohm, 1/4 Watt, 1% tolerance resistor from most any electronics dealer, like Digi-Key, Mouser, Newark, etc.

Another FasTrack switch mystery.  Some (but not all) of my FasTrack switches have a 1-1/2 inch thin wire going from the base of the lantern to the nearest rail.  I cannot fathom its function and it is really tricky to put back in once the switch stand assembly is moved.  Are there any words of wisdom out there?

Thanks!

Detail part that was not required.

Here is a further note to my dead fastrack switch problem.  I had measured 4700 ohms for the inline 2-ohm resistor and thought that the wrong resistor had been installed.  Nope!  When I cut away the heat-shrink, I found the charred remains of the resistor.  I have now seen a number of posts about problems with this resistor.  Does anyone have any idea what would cause it to blow (other than a user miss-wiring the switch)?  It would imply a pretty big current through some part of the PCB.  I hope my PCB is not destroyed!

The resistor failure may have been caused by transient voltage spikes that occur during derailments.  These spikes can approach 100 volts and are generated by the collapsing magnetic fields of coils in transformers, solenoids, electromagnets, etc. when the power is suddenly interrupted.

Do you have TVS (Transient Voltage Suppression) diodes installed on your layout?

If not, they're highly recommended to prevent damage to sensitive electronics like those found in modern locomotives, fastrack switches, etc.

Also, if you do need to replace the control board in the switch, they're only about $23

Here's a link to the part from Lionel:

https://www.lionelsupport.com/...FASTRACK-SWITCH-TMCC

The order of 2 ohm resistors from DigiKey came today.  I put one in the dead switch and it came alive!  I also had to adjust one of the micro switches to get the green LEDs to light in the controller.

My thanks to all those who gave me suggestions!

I do not know how TVS diodes could be configured to suppress transients in an AC environment unless they are put after the 2-ohm resistor inside the FasTrack switches.  Or are the suspected transients really greater than 20 volts?  Has anyone measured really high voltage transients on an AC train layout?   BUT I am suspicious the actual problem might be a simple derailing short that applies center rail power to the non-derailing control rail.  Without a detailed circuit diagram of the printed circuit board, this hypothesis would be difficult to investigate.  Has anyone verified the cause of the blowing of the 2-ohm resistors?