Are RF suppression chokes/capacitors used in Japanese models?

[Ken Ford]

I popped open one of my new Tomix HO Hakone Tozan Type 3000s to start diagnosing rough running and found a little circuit board that was inserted in series with one of the motor leads.  The board has what I think are an MB6S bridge rectifier, a 1N4004 diode and an unidentified third component.

 

Since this was in series with the motor and not across the poles I supect this is some kind of RF supression like I see in my UK models?  It doesn't affect the lighting that I can see.

[kvp]

While some models do have capacitors, a bridge rectifier and a diode is usually not part of such filter. If you could post a few photos of the circuit (both sides), then maybe we could make out what it does. Also i'm rather surprised that it's connected in series. Sometimes a diode bridge with it's DC sides tied together and connected in series is used to drop voltage for a motor, so the starting voltage is moved higher. This is used to allow the lighting in plain DC operation to fully turn on before the motor starts to move, to limit the top speed or with low voltage motors to limit the maximal amount of voltage getting to the motor. Is there anything else connected to it?

[Ken Ford]

No, nothing else - it's a puzzle.  You could be right, it limits top speed.  Let me compare the running speeds of the two cars and see if they differ. Thank you for the tip!

[Ken Ford]

OK, it appears to be a voltage drop circuit - good call, kvp.  I'll research the Canon motor to see what voltage it is rated for, but I suspect it limits the top speed instead of matching the voltage to the motor.  In my case these will likely get DCC which I can use to limit the top speed.

 

Thanks, kvp!

Edited February 21, 2015 by Ken Ford

[Ken Ford]

For future reference, here are  pics of the board in question both mounted and removed:

 

 

 

[mrp]

Talking about rough running, I stumbled across a couple of blog entries regarding the Tomix Hakone 3000:

http://ameblo.jp/c5711/entry-11961185682.html

http://ameblo.jp/c5711/entry-11961447166.html

It seems this guy was also a bit disappointed with the motor (actually, he says the shop warned him about it prior to purchase), so he disassembled the whole thing to try and work out what was going on.  He appears to have concluded that the fact that the motor is 3-pole - combined with the size of the permanent magnets - isn’t conducive to smooth startup and operation.  In the second post - to try and make the train start more smoothly - he takes the extreme step of reducing the size of the magnets (by fracturing and reinstalling them), and amazingly enough claims that it makes a noticeable improvement!!!

[Ken Ford]

Hmmm, that doesn't bode well. It might be time to consider remotoring with a Sagami.

[kvp]

It's a 3 pole straight wound motor. Fairly classic, but with a low frequency PWM drive or the proper DCC decoder, it could run very smoothly. (i've used a 100 Hz PWM drive to make 40 years old Z scale trains with ancient 3 pole motors crawl very slowly) If the lighting is led based, then the small circuit could be used as a starting voltage increaser/top speed decreaser (between 2.1-2.7V), which means the 3rd component is for short circuit protection, so a short or stall of the motor won't destroy the diodes. In short, i wouldn't change the motor, just use a better controller that can control old style motors well.

[Ken Ford]

I think that's a good approach, kvp - I've had DCC decoders work magic with balky locomotives.  At least if I do end up needing to replace the motor, the size and mounting are such that it shouldn't be difficult to do.