Hi, Fred-san,

In Japan, the problems occur these 2 years or so. Old motors are no problem, but newer motors failed very often. I guess they are due to the qualty problem of micro swithes.

First, I thought that failed motor should be thrown away.

http://nagoya-maerklin.f...p/railmaintenance_06.htm

But now I think failed motor should be remained and its terminals should be bypassed, because the micro switches stabilize the rebound of motor shaft.

Anyway the duration time of Solenoid Accessories in CS should be set carefully.

Fred,

this problem has apparently been solved now.

Hi all,

The problem with the 74490's is a bit (or a lot) more complex then meets the eye. When your turn-outs don't switch over there can be a number of causes. The first and most common one is just lack of electrical power as is often mentioned also by Märklin themselves. More often then not aggravated by a sticking or dirty turn-out mechanism. The second cause certainly with the older 74490's having a single double-action microswitch, is... too much electrical power. It causes the solenoid plunger to bounce back at the end of its travel. An additional cause can be the microswitch itself. Either it switches off too early or not soon enough in both cases leaving the turn-out at a half-way position. In reality there is a delicate balance between the speed of the moving plunger and the moment the solenoid is interrupted by the microswitch and we find ourselves again confronted with root causes 1 or 2.
Meanwhile, most märklinists know by now that shorting out or removing the microswitch solve all these problems so we automatically assume that the microswitch is the culprit. It isn't but taking it out makes the switching action far more tolerant for both root causes numbers 1 and 2 and far less tolerant for analog switching...

As for contact arcing as described by Fred and many others in various places, indeed that causes contact wear and thus a reduced life span. However, this type of switches normally have a lifespan of 100000 duty cycles, at rated load, even the el-cheapo ones. So if that arcing cuts that life span in half, you're never going to use it up anyway. okay yes, YOU are the exception :-)

But hold on, there is yet another phenomena. And it is back to root cause number 1: not enough power and infrequent switching. That results in a build-up of dust, dirt on the contact surfaces which is not burnt away by the switching action and, indeed, by arcing across the contacts. So, a bit of arcing is indeed beneficial for reliable switching action and that arcing only occurs when sufficient power is applied at... closing of the contacts. For more interesting literature on this subject see:

http://relays.tycoelectr...tes/app_pdfs/13c3203.pdf
http://relays.tycoelectr...tes/app_pdfs/13c3236.pdf

Best regards, Robert

Edited by user 10 February 2011 23:19:50(UTC)  | Reason: Not specified

I have had the motor stick

see thread
https://www.marklin-user...px#post262656#post262656

This is a major annoyance especially when your turn out has been ballasted down and really bad if it is from one of the first batches of C-Track and it breaks when trying to repair. Also you would expect more quality for the price.

Hi Darren, others,

Märklin has been working on these motors and modifying them ever since they were brought out. The new version 74491 according to Märklin has a new type of switch in them. Whether that solves all the problems??

What I tried to point out in my previous post were the causes of these problems. Once you have these motors built in you don´t want them to fail after only a short period of time.

To prevent that, there are a number of things you can do:
1- Take out or short out the microswitches but only if you switch your turn outs digitally with controlled/limited max. actuation time. (not possible with the old keyboard and 6021 or Intellibox 1).
2- Use the Viessmann 5211 decoder with their DC power module (5215) to power the motors. Or use any decoder, including good old K83 and feed the motors separately with 18-22 Volts DC similar to the Viessmann setup*
3- If you use analog switching use a separate 16V transformer dedicated to switching your turn outs only and use original purpose built pushbutton switches, Märklin or another good quality brand. Don´t put your elbow on them...
4- Always make sure that the mechanisms are clean and free. Collected dust combined with sticky oil dripping off your loco´s or coaches can be detrimental.

What you shouldn´t do (sorry Fred) is try to put capacitors or diodes into the switches in an effort to suppress the contact sparks.

The Viessmann C-rail turn-out motor has a built-in decoder and therefore no microswitches. A big advantage in this respect. Except for the price of course.

* When using digital power to switch the motors you are using a pulsed power, half of which is filtered away by diodes inside the decoder before it reaches the solenoid. K83 decoders and all other MM format decoders can very easily be modified to separate the digital signal for addressing the decoder from the power to actuate the motor solenoids. It can also be done with 74460 C-rail decoders.

Regards, Robert

Edited by user 12 February 2011 11:16:28(UTC)  | Reason: Not specified

...however, on the last generation of 74490 - at least since april 2010- may be before - according to some pictures, it seems that it's what Marklin did : they have installed a small capacitor on the PCB at each end of micro switches...
Moreover on a French forum , one guy said that he had been doing it a long time ago on older turnout motors : he has installed a 0.1 µf capacitor with the goal to prevent micro switches being dirty too quickly (because of micro sparks caused by "ruptured current"...sorry...it's my English...), then he made some endurance tests and obtained very good results.
-
According to someone who ask Marklin at Nuremberg toy fair, 74491 is said to be improved for more endurance , specially for including it into "Marklin - My World" range , as young customers used to try them very roughly & intensively....

Spot on Tom, that is what I think too.



Well, that is always the trouble with these endurance tests, you do a large number of switching actions in quick succession and it works beautifully. However if he´d run a blind test parallel to the test with the caps, it would have given equally good results.

To quote myself in an earlier post (sorry):

The way M has constructed 74490 is such that the plunger has an extremely long travel. For a reliable switching action it therefore needs powerful solenoids and a long metal insert in the plunger. That makes the plunger heavy. At the same time, they had to consider heat management of the coils under power, which comes at a premium because of the height restriction so as to fit into the C-rail turnouts and it being completely surrounded by insulating plastic. This and the requirement for both digital (short pulses) and analog switching results in a design that:
A- cannot tolerate power-up periods of longer than about 0,5 a second unless you intend to fry eggs
B- the long travel dictates a high current to actually get the plunger from one end to the other, which occurs at high velocity.
C- at high velocity, the heavy plunger develops a high kinetic energy at the end of its travel which must be destroyed in about 2 microsecond just before reaching the end of its travel, if you don´t want it to bounce back again
D- this is also where the microswitch comes in, it cuts the supply just at the right point of the travel, but only when the power is sufficient to get the plunger all the way across.

That means that the power rating of the microswitch must be relatively high, about one Amp. In fact it is only 500 mAmps, with gold plated contacts. There is a good reason for the underrated switch, because that way M had hoped that the relatively high current will keep the contacts clean by sparking, so long as the voltage is 16V or higher. A higher contact rating would theoretically give an increased life span but not without regular problems with dirty contacts. A well-known phenomena in switching contact design. M sacrificed longevity here for reliable switching. However in many cases the switching voltage is well under 16 Volts and thus no sparking at all occurs and collected dust and other contaminants don´t burn off resulting in malfunctions.

Frankly, M hasn´t been able to get to grips with all these requirements and during the time since 74490 was introduced they experimented with at least a dozen different modifications, involving the (placement of) the switches, the power of the coils, adding resistors, modifying the plunger and what not. Regrettably all with very limited succes...

I guess we all hope that 74491/2 will finally solve our problems...

Best regards, Robert

Hi,

I've had the same problem and started to disassemble (very carefully) the switch motor, opened the microswitches and cleaned the contacts. Apparently it solved the problem but, after a while, it came back again. Now I simply put 18 V DC on them as a regular operation voltage and if that is not enough I pump up till 24 V with an aux. trafo I have. I know it's a bit risky, but I got tired of taking off the switch, repairing and putting it back again. Now every switches are working and none has burned yet.
24 V it's a lot, but for a very short period of time...

Rgds

António

Hi Everyone,

I'm not sure if my problem is the same as what has been talked about in this thread, so here goes - Some of my turnouts don't work correctly, i.e. when I change direction by means of the CS2 the turnout changes and a few seconds later is switches back by itself. Does anyone know what the cause of this problem?

Greg

Hi,
Somebody reported the same behaviour as for the 74490, on a french forum:
http://www.3rails-forum.org/t69...491-toujours-pas-fiables

Fred

Robert,

can you give a little more detail on this?


r/Thomas

A quick tip that removes some pain when replacing solenoids on laid/ballasted track/turnouts:
Before installation, put one turnout upside down, put a piece of paper on top, draw around the turnout, outline the motor, use scissors, and you have a template.
Put the template where the turnout are placed on the layout, mark the motor-placement, cut out a hole, and you can access the solenoid and others from under your layout if any need for servicing.

Or use Tortoise-motors, or servos.
Easy installation, and lower price.

Hi Thomas,
When using the 5215 Viessmann powermodule, connect the 5215 output brown to K83 input brown. On the K83 turnout connections, do not use the middle yellow connection. The yellow wires from the turnouts (all 4) are connected to the E (red) connection of the 5215. The blue:s go on the K83 red and greens. That's it.

The 5215 is nothing more than a full wave rectifier w. smoothing elco, E= Minus and Brown = Plus. When making one yourself, make sure it is a full wave rectifier with smoothing capacitor.

Ps: Using 16 V AC directly from a separate transformer also works, again brown on brown and red (yellow) on the yellow turnouts, but doesn't solve the problem because of the diode in the K83 you only get half wave on the turnout motor.

The same trick also works with the C rail buit-in decoder.


Regards, Robert

Tutorial how to fix a C-track Märklin turnout:

Yes, it is the same fault, why K track turnouts stop working.

Moritz

So question remains how do you modify these new version of turnout motors, if you wish to do?

Any talk on stumi on issues modifying the new turnout motors?

Brgds Lasse

Martin T posted a video on April 1st how to repair these:

https://www.marklin-users.net/forum/posts/t35563-Tutorial-how-to-fix-a-failing-Marklin-turnout----switch-motor-75491

Hi Lasse,

Did you try reversing the modification? If you put them back how they come from the factory do they work or not?