Lego Duplo locomotive stops after 1 second

[Robr]

I was asked to repair a DUPLO locomotive (52088) The one that has a rotary sensor at the front axle.

The problem is that when I push the top button the horn sounds and it moves forward for 1 second. Then stops. Every time....

When I push fast two times the stopping sound also works and the wheels stop directly.

I've dismantled it and looked if the reed sensor was defect. But that works good.

I looked at the motor unit but do not see any strange things.

The water intake "sound" works fine.

When I bypass the print plate and put the + at motor directly the motor runs fine too.

I cannot find what makes the motor stop every time

What could I check or do more?

Sincerely

Rob

Edited November 10, 2013 by Robr

[JopieK]

Can you maybe upload pictures? That would help. Better also try to find or reproduce the circuit.

[Robr]

I'll try to do the pictures. The one from my iPad are too big. I'm no Elektro technician so to reproduce the circuit will be a challenge...:0)

[JopieK]

now and then it is a challenge since often manufactures seal the chips... I'm suspecting a motor driver IC is the cause. (not an electrical engineer myself, but do teach Informatica / Embedded systems so have some professional knowledge).

[NoEinstein]

I bought a new Duplo train for my nephew a few years back. I tested the locomotive to prevent disappointment when playing with the present after opening it.

I put batteries in it, pressed the run button and it had the same behaviour you described. Then I put the dang thing on the ground pressed again and I had to chase it through my room. Apparently there is a pressure sensor in those trains to prevent, I assume, kids hurting themselves when the wheels spin without touching the rails/ground.

You say it moves forward 1 second so I assume you put it on a surface, but if not you might have the same problem I experienced and almost made me claim warranty.

[JopieK]

It is an older version but it is always a good ice to check with LEGO for a replacement. My brother in law has good experiences with that (accidentally one of my nieces drowned the train in a bucket of water ;)) although he told LEGO the cause, they just replaced it without any charge.

[Domhnall]

On 11/10/2013 at 2:09 PM, NoEinstein said:

Apparently there is a pressure sensor in those trains to prevent, I assume, kids hurting themselves when the wheels spin without touching the rails/ground.

NoEinstein, thanks for this info. Saved me a bit of a headache repairing an eBay purchase 3 days before xmas. Let me know if you have Venmo or something; I'll buy you a beer.

[JopieK]

@Domhnall: this is a topic from 2013, so I guess the original poster @Robr  either found a solution or his kids are probably too old for Duplo in the meantime, welcome to Eurobricks but please adhere to the rules.