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H0 Scale Train Repair? Answered

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I have old train from Marklin Hobby 2905 set 
When i turn on train PSU i can hear relay working but train doesnt move (motor doesnt work) 
I have tested motor with multimeter and it beeps (coils are ok) and when i tested electromagnet it also beeps
Can somebody show me how to repair it?

19 Replies

user
iceng (author)2014-06-26

This is an older engine, made before NIB magnets, way back when the magnetic field was made with an electro-magnet as a shunt field winding or perhaps a series winding.

Either way that field winding is wire dead.

I would disassemble that part of the motor and unwind the field counting the turns

and measure the wire gauge on the cleanest wire segment. Then rewind the field and try running an undamaged motor.

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user
iceng (author)iceng2014-06-27

BTW excellent photo work !

I can see one of the brushes is OK meaning both are in the same OK condition.

And for future reference,

I / we call that kind of thermal damage a "CRISPY CRITTER"

It would take me 16 hrs to re-wind this machine.

I hope the armature windings are not in a similar damaged condition.

A coil burns out like that, if it was over voltaged or stalled for a long time.

It definitely made a bunch of smoke when it was fried.

Are there smoke candle like smudges in the engine cover inside surfaces ??

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tutdude98 (author)iceng2018-01-20

I had some time so i disassembled whole motor and it looks like 1 of the 3 windings on rotor is burned so you were close, anyway i think its gonna stay on my desk as it was for 3 years, not working :)

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iceng (author)tutdude982018-01-20

Sorry, but it is a New year..

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tutdude98 (author)iceng2014-06-27

I have put leads of psu directly to coil and slowly raised voltage and put magnet closely (AC voltage so magnet shakes) and it works so i dont belive that theres problem

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iceng (author)tutdude982014-06-28

OK not dead but IT IS compromised making a weaker magnetic field

which if the armature is in good condition will make the armature turn Faster.

I can only speculate based on your clear pictures.

Yet you say it does not run !!

Remember continuity in a wire coil does not guarantee a winding without a partial group of shorted turns inside.

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steveastrouk (author)2014-06-27

This is what you should have. Can you measure continuity from one wheel throuigh the motor ? Or where ?

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tutdude98 (author)steveastrouk2014-06-29

You have one contact on wheels and one is on metal plate that under train

I can measure continuity on one side of motor and metal plate (but not on coil) and i can measure on wheels and other contact on motor but i also beeps on all three contact that i have on coil

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steveastrouk (author)tutdude982014-06-29

You have my picture. Mark it up with where you have continuity. Use the words armature to describe the bit that spins and coil to describe the bit that doesn't.

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tutdude98 (author)steveastrouk2014-07-01

i have three contacts on coil (not two) and it looks like the second connection goes to motor (the one in the middle)

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user
iceng (author)steveastrouk2014-06-28

Nice schematic of the shunt motor

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user
steveastrouk (author)iceng2014-06-29

Thank you. I've decided to try and raise my game in the face of your excellent diagrams !

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steveastrouk (author)2014-06-26

Have you tested the TRACK with a voltmeter ? Have you checked that the volts appear at the motor, when the train is ON the track ????

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tutdude98 (author)steveastrouk2014-06-27

track is good becouse i can hear relay working and i checked voltage on motor i can read it but theres no voltage on electromagnet

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iceng (author)2014-06-25

The brushes could be worn-out because i don't see any part of them in the brass slides. See if you measure the same voltage across these as the rails ?

The turning motor armature could have an open coil but still show continuity.

I would try to see if the armature doubles or halves its resistance as you slowly turn the motor shaft, this would indicate a broken armature coil or a really bad contact brush.

The noise suppression CAPacitor could be shorted..

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tutdude98 (author)iceng2014-06-26

I have removed rotor and check three brass tabs and all show that coils are ok

I think that motor is working and i think that problem is in switching becouse on psu i have variable 0-16v and 24v when i put on 24v voltage is high and train should go backwards ( i can see that becouse relay turns on only when i put on 24v and when i put it on 0-16v relay is turned off)

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steveastrouk (author)2014-06-25

Can you turn the motor's armature by hand ?

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