I have had 2 of the 74490 switch-motors fail completely - and that is a very high failure rate since I only have 4 such motors in total. The problem is that the end stop micro-switches go open circuit (have measured this with a multimeter). When I move the switch forth and back a few times it may start to work again, but do eventually fail again.

I use the Viessmann 5231 decoder for digital operation. When replacing the switch motor with a new one, it works just fine.

Have anyone else experienced such problems?

-Roger

Thanks for your feedback Charles. I did buy the switches at the same store, but they came from different batches according to the date and revision codes on the internal circuit board.

I have investigated the problem further and found that the micro-switch contacts were badly burnt. The picture below shows the internal parts of the turnout switch, with insets of the open micro-switch and the burned contact. I fixed the problem by sanding the contact points lightly and then assemble the micro-switch and solder it back in place. So far it works fine.

So why did the contacts get damaged? Thinking of it I actually find it quite strange that this does not happen more often. The current trough the coil is around 1 A and when the contact opens there will certainly be some arching across the contacts due to the inductance of the coil. And 1 A is quite high current trough such a small switch.

Since I use a decoder the current trough the coil is DC. This is probably a bit worse than using AC, which I assume is normally used for wired switchboard operation. Could this be part of the problem?


Open Turnout Motor with burned micro-switch contact

Hi,

I don't quite share Ron analysis.
In fact, after making some measurements, it appears that the current in the coil is switched off after 20 to 40 ms. So, even if the energizing time is limited to some hundreds of ms, it's the end position switch that switches off the current. Then if the switch can't withstand a 1A -or so- switching current, the problem will appear soon or later.
(I agree with Ron on the fact that if the microswitch doesn't work and stays in the "ON" position, the coil will burn (or the plastic close to) if it is not de-energized)
I personnally have not had this problem for 3 years with my 74490 (energized with 16V AC), and AFAIK this problem is not often (if any) reported on this forum.
So it's may be a quality problem on new micro switch?
(Hope it never appears in my hidden station!)
If it's really a quality problem, and if it is not seriously solved by Marklin, I see only 1 solution (except not using 74490): it's to remove (or shunt) the microswitches, and use, of course, a pulse to drive the coils.
It's for sure the way I'll go in my next (?) layout.

Using a non-reliable turnout in a layout is not acceptable.

Roger, if you were kind enough to send back the burnt switches to Marklin, and try to get from them an explanation, it would really be profitable to the whole Marklin community.

Thanks and best regards

Fred

Viessmann posted a video on youtube showing 4554 slow moving motor in action.

The design is impressive, can't wait to see it working with the C-track

https://www.youtube.com/watch?v=JbbQTgquiNg