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Zimo MX634R loco runs then slows and stops.


Michael Delamar
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I have an issue with a new Zimo decoder I have installed in a recent kit built chassis.

 

It is Comet chassis with coreless Portescap motor, I have used this same decoder in many other locos with the same motor, in fact I have standardised on using these decoders as I like them, I must have about 20 portescap fitted locos with them.

 

This loco is a new build and it will run fine around the layout for a certain amount of time, then It just slows and stops, as if it has ran out of steam! Give it a minute and it will run but then do the same, try and hurry it and it will only run a short distance. 
 

My first thought was that the kit built chassis or motor gearbox may be tight and running hot, but it isn’t,  it’s very free running. 
 

Im therefore wondering could it be something in the settings that I could adjust?

 

thanks for your time.

 

Mike

 

 

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Just wondering if it is indeed a chassis issue that's causing excessive current draw, and that's causing the decoder itself to run hot and shut down? Do you have any means of measuring current draw on the layout via your command station?

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I use Roco for the layout but use a NCE powercab for programming locos although I never change anything other than addresses. If the NCE is capable of doing that I could try it but would need to be talked through it or read up first.

 

I should have said the loco is hauling a train when this was occurring but nothing excessive. About 15 wagons.

 

 

 

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Does it do the same when running light engine?

 

The NCE PowerCab will most definitely indicate the current draw as an alternative to the time display. Press the Esc key followed by the number 6 key and then press 1 to get it displayed.

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I suspect one of two things: 

 

a)  a short somewhere, either in the motor, or elsewhere in wiring, which is leading to high current draw, which is overloading the decoder.   Could be a stray-strand of wire, or something touching somewhere.   Being a metal loco/chassis, contact is more likely to be a problem. 

 

b)  faulty decoder.  

 

 

 

Whilst ( b ) could be tested by removing decoder, and testing elsewhere,  diagnosing ( a ) would be much harder as changing anything is likely to change or remove any contact errors.  

My thought would be to swap the decoder for one known to be good, or try the decoder in a different loco.  

 

 

As a choice of decoder, the MX634 is over-specified for the Portescap motor/gearbox (assuming this is the type very popular in 4mm finescale builds from 25-40 years ago - bevel and spur gears and a small coreless Swiss motor).    The much cheaper and smaller MX617 should do the job with lots of spare headroom on current.  

 

 

- Nigel

 

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It was the motor!

 

I changed the decoder and the same thing happened right away.

 

So I changed the motor and the new one is fine, it’s a great runner and now had stay alive capacitors added, I don’t  normally add these until a chassis has had a run and its pickups etc adjusted.

 

The bad motor I ran on DC and the same thing happened it died, as it was stopping it made a low buzzing noise.

 

All I can think is that these motors were bought a while ago as new old stock and they’ve sat round for ages and never been run in properly.

 

After a while I’ve now managed to run this motor for half an hour both ways full power on DC and it’s a good runner now with no issues.

 

The chassis was one I built on the workbench during lockdown and only now I’ve been able to set the layout up and give it a proper run.

 

im glad it wasn’t the decoder, Ive got loads of these and not had any issues with any.

 

Thanks all.

 

 

 

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21 minutes ago, Michael Delamar said:

It was the motor!

 

Glad you found it.    Sounds like it was failing as "open circuit", hence no over-load seen anywhere.  

 

Many makers have motors with the same screw-nose, so different motors can be swapped if you just move the bevel gear to the new motor.  

 

 

 

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