Runaway MTH Dash-8

Hi Press I'm no expert , but clean all the rollers and wheels on the engine

make sure pick up rollers are tight. Check the battery. That's about all I

can help with. You will need some of the expert's on this forum for more

info.

THANKS, ALEX

I had an engine do something similar and it was the tape strip.  Pretty creepy - it would run jerky up to about 8-9 SMPH, then smooth out up to 25, and then one click over 25 and it would take off like a rocket.  I almost put it through a wall.  The MTH tech who did the conversion made a few small adjustments and now it runs great.  

Take another look at that tack strip and the wiring. What you describe is a good indication of a failure of the tack reader. Everything is fine until the engine is commanded to move and then it increases in speed because the tack reader is not seeing any input from the reader. Again, checking the wiring.

Al

You might need a magnifier but take a good look where the 3 wires attach to the tach board as shown in lower right below.  For example, one strand of wire may have come loose and is intermittently touching another connection.

As the tach tape looks clean, also confirm the distance from the reader to the flywheel and remove any "gunk" that may have accumulated on one or both of the reader windows (the shiny black rectangles).

The guys are correct on what you should check.  The readers do go bad and will give you what you have.  Just before replacing the reader, hit each wire with a hot iron after removing it from the holder.

One more thing on the side of your board where the power/ground and tach wires plug in, reseat the plug.

Hey guys,

Thanks for all the feedback thus far.
I opened up and took another closer look at the tach and associated reader. Spacing of the reader and the tach looked to be acceptable.
Again, nothing overtly obvious could be seen with the actual tach. I wiped the circumference of the tach down, just to be sure and also gently wiped the reader.

I took a real close look at the wires going into the reader. As you can see from the pictures, there's no inadvertent contact causing any sort of short. As best I could I tried to follow their run back to their plugs and all looked to be in satisfactory condition.
Put it back on the track, and had no success.
Any other basic troubleshooting recommendations, or is a trip to the local MTH tech the next order?

thanks again for the assistance lent so far!

-Joe

I had this happen when I first hooked up my dcs. When an engine just took off running full speed. Found out that I was pushing down on the thumb wheel which in dcs runs the engine up to max speed had to go into the various settings in the dcs and turn this setting off by default it is on. I think by default max speed on all engines is like 125mph which makes them really fly down the track. I don't know what you would use the run to max setting for? But I have a heavy thumb and had to turn it off. After this happened a few times I also lowered max speed on all engines to 70mph.

I like Nelson's answer. I don't know if it's right but I like that answer. 

I had problems with an MTH engine that I thought was the tach reader. It turned out that the battery was worn out and after replacement, all worked fine. (the engine was about 5 years old) This may not be the cause of your problem, however it may be worth removing the battery as a possible cause.

JoeK

Nelson,

Found out that I was pushing down on the thumb wheel which in dcs runs the engine up to max speed had to go into the various settings in the dcs and turn this setting off by default it is on.

Sorry, that's not quite right.

What you were doing is activating a feature called "Quickset Speed", which actually works like this:

• Press the thumbwheel once and "Quickset Speed" appears in the remote's LED window
• Enter a 1, 2 or 3 digit SMPH on the remote's keyboard
• Press the thumbwheel again and the engine will accelerate or decelerate to that speed

 Quickset Speed may be disabled from the Control Menu.

Hey folks: Unfortunately, this saga continues.
I wound up taking this misbehaving engine into the local MTH repair shop to be looked at.
In what was an embarrassing display, the engine behaved correctly the entire time, responding to DCS speed controls the entire time. It was even brought from the test track to their layout display and ran fine. The tech couldn't pinpoint a smoking gun or anything to even really keep an eye out beyond what has since been recommended here on the forum.
I was even able to bring the engine home, set it up on the layout and have it work fine.

But this lasted for only about 20 min.

I had it running at about 32SMPH and then out of no where, like the first time a brief burst of uncommanded full throttle, before coming back down. Then a few minutes later a complete runaway. Now it's back to being a total runaway just by dialing in 1 SMPH.

The ONLY thing I noticed that was done to the engine while in the shop that may have had any effect was that when the engine was first being inspected in was done so in a conventional set-up before the DCS set-up was brought out.
The power level was cycled a few times to change the direction and it ran fine. When the DCS was hooked up in the shop, it ran fine as well.

So does this tell any experts anything more about what may be going on with this engine? What would being exposed to a conventional set-up do to change how the DCS circuitry behaves?

-Joe

Joe,

To me it still sounds like the tach reader. Check the wires from the reader to the board and make sure they are tight and seated well and don't have any breaks or the wire is pinched.

Being ran in conventional won't change anything in DCS.

Here's another thought. when it does this does it only do it in one direction? If so, there is enough movement the armature can travel up and down. When the motor starts to turn and with the worm drive it can make the arm and the flywheel move up and down. So what could be happening is the arm and the flywheel move up just enough that the reader loses contact with the flywheel.

One thing you can do is move the flywheel down a bit on the arm, or you can lift up the reader just a bit. Just ot check, turn the motor by hand and watch how far up the arm moves and adjust it from there. If you move the flywheel be careful so you don't bend the motor shaft.

Ralph

One way to test stuff like this is with a set of test blocks.  I find myself using these a lot to work on locomotives, makes it very easy to run them and not risk them getting away.  You can also work on them as they run, very handy.

Best $65 I have spent recently on tools.

Good point John.  Per the Micro-mark description for their $59.95 O-gauge test blocks :

Makes it easy to detect, isolate and repair erratic operation so your locomotives will run smoother than ever before.

Got an email from them today claiming Free Shipping on orders over $50 thru May 15.

I like the JAK block set I got, two of them had the 3rd rail contact.  One complaint, and it looks like the ones you reference have the same issue.  Occasionally, you'll find a locomotive where the pickup roller is not close to the wheels, then the blocks miss it.  I use a clip-lead to connect the center roller in those cases, but it would be nice to have an extended roller contact on one of the blocks.

Press2MECO  Did you ever get your speed control problem fixed? I have the same problem with one of my MTH PS2 Berkshire Steam Engines. Thumb wheel it to 1 MPH and it launches like a rocket. Everything else works correctly.

Guyeh, try running the loco in conventional, see if it chuffs and has puffing smoke. If not, the tach board either has a bad connection or is kaput. Also look at the stripe on the flywheel, see if the stripe is intact. Replacements are available. Replacing the tach board is fairly easy, and should be inexpensive. If I can help LMK. Luke

I had the same problem with a LoV subway car and returned it to MTH and they replaced a part on the board and it runs perfect now. The charge was reasonable also but it was there like 8 months.

Thanks for the responces. I ran it in conventional and it chuffs and puffs smoke. The brake squeal also stays on the whole time it runs in conventional or command mode. The stripe looks good also. Any other suggestions?? Thanks...

Apparently you can alter speed in conventional by adjusting voltage.  At a slow enough speed you should be able to confirm 4 chuffs & puffs  (or whatever you set it at) per wheel revolution.  If this is true, then your tach is probably working.

If so, then the symptoms point to a problem in the motor drive electronics - for example it is only driving the motor full-on or full-off rather than controlling speed.  So when on, it could be applying full rectified track voltage to the motor.  This correlates with the brake sounds which was a key observation on your part. That is, braking sounds turn on when the processor detects it is going too fast (from the rate of tach pulses) and needs to slow down.  The runaway engine problem caused by a broken tach typically delivers NO pulses so the motor takes off trying in vain trying to get some tach pulses; there is no braking sound if the tach is not returning pulses.  Probably more information than you want...

Anyway, if the motor drive is indeed your problem I don't know if there's an easy DIY solution. If you are set-up to poke around electronics with diagnostic tools, then we can go down that road.  Otherwise I'd think this is best left to an authorized MTH repair shop.

Do you know or have the paperwork showing which part they replaced?

U-12 on the power supply board.  G

I dropped it off at the repair shop today. He put it on his track and it took off full speed on 1. I'll let you know what they come up with. Had no estimate on how long it will take.

Well I got my MTH PS2 Berkshire Steam Engine back from the repair shop today. Right at two months for repair. Said the processor board was bad and replaced it. Length of repair time was due to having to order the board. $106.25 for the repairs. Working great now and I'm happy. Thank you to the people that tried to help me and I hope everyone has a Merry Christmas and a Happy New Year....