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@frBob posted:

I have a RailKing MTH BN C-30-7 with PS-3 that has begun taking off at full speed when I apply power. Well that's not good!!!

Any fix? Sure, there are replacement boards, replacement tachometer sensors, could be a wiring fault, could just be the tach sensor misaligned and no longer able to read the flywheel stripes.

What am I doing wrong? The huge mistake is you trying to run it after you discovered the fault- somehow hoping it would fix itself. The risk is further costlier damage. The smart thing to do is STOP- send it to a tech. Minimally remove the shell to examine the flywheel and encoder and all wiring. Also, should use a current measuring supply to note exactly the power drawn when powering the engine. This could indicate a serious short.

It has run well for a couple of years (although it does not lash as well as other PS-2 engines)

Again, the problem is, this might be simple or it could be a wiring fault. Failing to detect a short could lead to further problems and further cost.

Last edited by Vernon Barry

While this is an upgrade kit instruction, this is also very basic and good advice for both PS2 and PS3 engine troubleshooting.

https://mthtrains.com/sites/de...ction/50as18328i.pdf

Testing The Proto-Sound 3.0 board and wiring Upgrade Installation


- Place the engine chassis on a test section of a track.
- Apply 12 volts of power (in conventional mode) to the engine. If you have a
Z4000 look at the current display.

Turn the smoke unit switch off and power up again in conventional mode. The engine
without the smoke unit on should not draw more than 1.0 amp.

With the smoke switch turned on, the engine should not draw more than 1.5
amps. If the engine draws more than 1.5 amps, shut down power to the engine
immediately and check your wiring for any pinched or cut wires. Troubleshoot
any problem in the smoke unit or wire harness accordingly.

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@frBob posted:

Cranked it up and did a factory reset and it seems to work just fine now. Thanks for your comments. I will verify the tach reader gap dimension.

I'm hoping you understand why I said what I said. When you suspect a serious issue like runaway or other problems, it's important to know how much power an engine is using, to determine if there is a short. This is because in PS3 and many other modern control systems- most any wire coming from the control boards cannot short to AC frame ground. In particular- one form of a runaway is when one motor lead shorts to frame ground.

Again, modern electronics that use a bridge rectifier- then DC ground is not the same as AC ground and any wire shorting to frame potentially injects AC back up into DC and often lower voltage controlled circuits.

Yes, a reset is a good troubleshooting step- but after you confirmed and know the engine is not shorted and not drawing excessive current.

Just trying to protect yet another PS3 system from possible damage and the cost of replacement. Again, glad you resolved it, speed control may have been disabled and the reset turned it back on.

Again, the above chart may explain how under conventional- a sequence of bell and whistle may have turned speed control off.

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Again, here's the problem:

@frBob posted:

I have a RailKing MTH BN C-30-7 with PS-3 that has begun taking off at full speed when I apply power.

I would think other people read that just like I did, that the instant power was applied to the track, the engine takes off and is uncontrolled. That symptom of taking off the instant power is applied- could be explained by a motor wiring short to AC frame ground. I know that might at first sound odd, but the forward and reverse control of both PS2 and PS3- one motor wire is always powered with a rectified DC source. The return path from the motor goes to an FET transistor that modulates the return power determining speed. Again, a motor wire shorted to the can of the motor or other frame metal- could be at frame AC potential voltage.



A better story explanation would be, the engine starts in neutral, I get the normal startup sounds, then if I drop power momentarily, the engine runs very fast at relatively low conventional throttle. That then sounds more like speed control disabled.

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