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Some customers who bought ESU class 66 or class 77 locomotives that are produced in 2013 (second production run), report problems when these engines are used on Märklin 3-Rail track: They find that the locomotives will just stop on track sections that are used together with (s88) track feedback systems. The reason for this behaviour is that on the engines affected, just the right hand wheels are used for power pickup. However, normally both side wheels should be shorted by an internal microswitch and used for power pickup.
The reason for the malfunction is a change in the internal microswitch is installed into the boogie and that is resposible for changing between 2-Rail and 3-Rail operation:
On the second production run of the engines in 2013, the metal parts of this microswitch are nickel plated to allow for better corrosion protection. As a result of this plating, the microswitch's contact pin has to be pushed with more force. However, the contact plate of the pickup shoe is made from POM and we noticed that on some occasions, it can bend in a way that the contact pin is not pushed down enough.
ESU will design and produce new power pickups that are stronger and ship to all customers affected by this problem. We will publish further information on how to get these new parts here soon. Please stay tuned.
In the mean time, you can help yourself by modifying the power pickup on yourself. It is quite easy to do.
First, remove the power pickup using the tooling that is supplied with each locomotive. Then, you need to use your soldering iron to create a solder tin ball on top of the power pickup's contact plate. The figure to your left shows the exact position of the solder tin ball. This area later has to touch the contact pin.
The solder tin ball's height should be around 0.5mm. Please be careful when soldering: Do not heat the copper base plate for too long time to avoid the melting of the plastic contact plate. You may decide to lift the copper pad first, then solder and then bend the copper pad back to the original position.
Finally, re-assemble the power pickup again. Please note that the tin solder ball has to push on the contact pin. Also make sure that the power pickup is mounted correctly: There are two detents on the locomotive that have to hold the contact plate.