Hello everybody!

This is my first post in this comunity and I hope to find out how to repair this old train (Image 1) I used to have when I was a kid. Firstly I want to thank you, who takes his time to help me. Let me explain you what's going on.

I have (as previously mentioned) a Lego train, bought more-or-less in 2005. The train has a button on it's top (Green cilinder in Image 2&3, board seen in Image 6), which turns the device on and starts off the motor (and some fancy sounds). It has two more buttons, which give each a different sound. There are two more buttons under the train (Image 8), which are used to perform some direction changes during the course of the train, or eventually to stop it*. The system can be turned off with the same button used to turned it on. The thing is, that all the sound and power system is working, but I can't manage to make the motor-system work; at least not as it used to (Clearly seen in the videos, motor should start once the power button's pressed).

I dismanteled the train, and tried connecting the motor with a low V battery, to see if this was the error. However, it worked perfectly and I'm thinking the error must be somewhere between the microcontroller and the motor. I am a Computer engineering student, so I really don't have the knowledge of an Electric/Electronic engineer; but I believe that could be where the problem is. I attach some pictures and videos to help understand whoever wants to help me the whereabouts of the problem.

Video 1
Video 2

Thank you for reading this and sorry for my broken english, I hope you can help me!

*This is done once the train's started, some plastic sheets could be placed wherever in the railroad, and the train would do different things such as direction change or stop depending on how long one of this buttons where pressed.

**Two disconected cables can be seen in the pictures, these are the cables that conected the motor with the board, I cut them off to check if the motor was working or not.

 

Can you read the writing on U1?

 

Can you read the writing on U1?

Yes, it's:
1930-1N8

 

I don't think that's going to help much - unless someone knows different?

It looks like U1 is controlling the motor and, possibly, the control signal(s) come through R3 and/or R4.
Can you measure the voltage between TP6 and the ends of R3 and R4 nearest TP6. Measure these voltages both when the motor should be running and when it should be stopped.

 

Right... I think I've got those voltages:

Motor Off:

TP6-R4: 0.01V
TP6-R3: 0.01V

Motor On:

TP6-R4: 4V
TP6-R3: 4V

 

So I think U1 is defective as it receives changing control signals but its output does not drive the motor.
Sadly, I don't know what U1 is and I can't find a possible replacement.

 

Anyway, supposing U1 is defective, why are sounds and other stuff working? Aren't they controlled by U1? And even if a replacement was found, can something be done without the software, but to try and rewrite it myself?

 

The 'brain' of the train is hidden underneath that black blob indicated below:

 

Oh! I got it, so the U1 just computes, right? I'm gonna look for this kind of IC then, 'cause the "brain" would still comunicate with another IC, right?

 

U1 is a motor driver IC. Read this to get an idea what it does - though the chip described is MUCH more than your U1.

 

Okay, thank you very much for your help and your time!