Joe,

Yesterday I had to lift part of my own track to extract the faulty mechanism from one of my turnouts.
I soldered across the micro-switch. Now it is working perfectly again and track has been returned to layout - all working fine now !

One must just remember that the purpose of the micro-switch was to switch the current off when the mechanism had switched, so this safety feature has effectively been disabled.

Regards,
John

No impact when using digital control; only in analogue you might burn some solenoid (depending on how you control the solenoids)

Hi Everyone

As a result of this thread I decided to change all my 74490 turnout mechanisms by shorting the switches to prevent future frustration on the layout I am building. All the 'fixed' 74490 turnout motors work fine and I hope that I will reduce any future problems, as access to some of the turnouts is difficult.

I am using a CS2 to control my layout and while testing the 'fixed' 74490 mechanisms I noticed that after the mechanism has thrown there is a short buzz. To me this indicated that I may be able to shorten the pulse length to eliminate this buzz. However I was unable to reduce the pulse length below the 200ms default on my CS2. It is possible to increase the pulse length. I was working on the Settings screen for the specific point used for testing on the Keyboard screen of my CS2.

Is 200ms the shortest pulse length possible? or is it a limitation of the 60830 decoders? Alternatively has anyone an alternative solution to eliminate the buzz?

Hi Mike!


Congratulations! I don't have that courage.


I don't realized that... I'll pay attention on that...


Same "issue" here. Which CS2 do you have?
Here is a 60215, with lastest firmware from Märklin.


Probably it's a software limitation... Maybe a standard from Märklin to guarantee that all solenoids will work...

Best regards,

Walter

Hi Mike!

I have the 60215 also, with updates from some (few) months ago. As I remember, the version it's the same (need to check, but 99% sure).


I have a little more than 40 turnouts (and 5 spare 'broken' motors) and after saw that video, I soldered all broken, and now they are ready to operate normally. On the layout, more or less, 8 motors was substituted by the soldered ones.

No issues till them. And happy not to need to send them to Germany.

Regards,

Walter

ps. Meanwhile, I'll solder each one that isn't operating as they are supposed to.
(do not fix that do not need to be fixed)

I installed sixteen 74490 decoders 14 years ago and they are worlking fine all these years.I installed four 74491 twenty days ago and one of them is allready broken.

I had my first 74491 failure The usual issue with the turnout getting stuck in one position...

I removed the small component and shorted the terminals.

Enclosed a few photos below (before/after).





Not being an electronic buff, why can’t we just remove the micro switch? What actually happens when we short the terminals?

I guess what I am asking is, instead of fiddling around with soldering, what would happen if you instead broke off the little plastic tap on the micro switch, in that way the switch would never be activated when the tong moves?

Brgds - Lasse

They are not totally useless since the off command from the controller might get lost on its way to the decoder, the decoder will not turn off the turnout motor and it might burn out.

They are totally useless with modern decoders that handle the switch off internally.
They are not normally needed with modern controllers that turn off after a period. But there were reports from users who heard a permanent buzzing sound from their turnouts because the off command had been ignored.

Better safe than sorry.
Some folks use separate boosters for accessories. This prevents micro-shorts caused by wheels or centre rail pick-ups from disturbing the solenoid decoders. If you don't have new decoders with automatic switch-off, this can also help reducing the risk.

I am still trying to figure out the electronic circuit of the mechanism when used with an external decoder like K83.

From my basic understanding:

1. A command is being sent to K83 to open one of the output ports for e.g. 250ms.
2. The K83 briefly energize the circuit
3. As one part of the solenoid gets energized it gets magnetised and draw the steel plunger toward it
4. Towards the end of the travel the plastic part of the plunger hits a mechanical switch on the micro switch.
5. The micro switch cut off any power to the solenoids to avoid accidental burnout.
6. The micro switch is also being activated a bit earlier to stop the plunger in its travel to avoid a bounce back?

Question remains then, when we bridge the contacts we basically disable the switch? And will bridging and physical remove the switch have the same result?

And finally when the internal contacts inside the micro switch gets exposed to sparks (predominantly in 74490 and attempted to minimize in 74491 by using a varistor) what actually happens then? The switch will always be on or off or cannot turn off because the contacts are dirty?

What I don’t understand is what is preventing the plunger to travel back when the other part of the solenoids gets magnetised. Everything seems loose and friction less so why would a faulty micro switch somehow prevent steel and magnet to meet up as it should do???

I am just trying to understand the electronic circuit of it all...

Brgds - Lasse

Hi All,

According to Viessmann's new items 2014 brochure, they will be reeling this year a point motor for Märklin C track. From the description it is already bundled with a digital decoder (can also work in analog mode). It's item number 4558.
Perhaps this can be a good alternative to overcome this long lasting issue with the 74490 turnout motors. Only time and experiments with Viessmann's new motors will tell. At least there's some hope...

Regards,
Pedro