As comment on my 8 March input under “Servo Motors as Point Operatorsâ€, ‘Penlan’, referred to problems of setting his system.

While ‘Penlan’ described his problem as related to changes in his mechanical linkage system due to the changeable conditions we meet under exhibition conditions, I considered that the problems I met were caused more by the servo being pulled from its true set position by the drag of the point tie bar.

Certainly I had more trouble with the double slip where the point motor is required to pull on a tie bar that actually carries four blades rather than the normal two. That said, the servos on the normal points did not seem to maintain their set positions on anything approaching a consistent basis.

However my assumptions that there was indeed a problem came about because the offending servos, when supposedly at their set position, emitted mechanical noise. To me that suggested that the servo’s motor was still running and struggling to hold set position.

I am reliably informed (by the MERG member responsible I think, for the Servo4 design) that the noise is caused by some electronic interference generally called “noise†by electronic techies, and that this is in some way caused by other cables adjacent to the ‘Servo4’ wiring. I was also told that it could be controlled by adding capacitors, but frankly, to me, that is introducing further bits and pieces to something I am already struggling to understand.

What I am looking for, and I’m sure, so too are many other railway modellers, is a point operator or motor to which I add some wiring and it works, I don’t wish to change my hobby to being an electronic expert! The MERG ‘Servo4’ system is, I believe, as close to that requirement as has yet been achieved. It’s a bit unfortunate that this “noise†thing seems to be causing us non-techies some problems.

I suppose I should admit to being a ‘techie’, but my engineering background is in heavy current electrical engineering as applied to heavy mechanical engineering and to electrical distribution. In fact the semi-conductor industry we know today did not develop until after I qualified, so as far as modern day electronics is concerned I don’t rate “techieâ€.

None the less, my electrical knowledge allows me to make some decisions and to have at least a vague understanding of what is happening on my layout.

I have to say that I’m doubtful about the reason for my mechanical noise being caused by some form of electronic ‘noise’. This is because if I ignore these sounds, then eventually the whole system stops working and I am unable to change any point.

I’m now fairly confident that this failure is due to the chip in the Servo4 board having some type of thermal sensing circuit which closes the chip down if the chip suffers a temperature rise which would eventually cause its destruction. That suggested to me that those servos emitting noise are taking a current which is beyond the chip’s continuous rating. What ever is the cause, having the point control system switch off without warning is a situation which is totally unsatisfactory, whether at an exhibition or simply at home ‘playing trains’.

To over-come this problem I added a normally open push-button switch to the 9V ac input to the ‘Servo4’ board, such that the whole system is only energised when the push-button is held down. This is working very well, but it is still a bit early to claim that I have found an answer.

Hold the button down, operate the point switch and wait until the blades have moved slowly into position before releasing the button. With that simple addition it is impossible for any part of the point changing system to be taking electric current unless the push-button is held down, yet, at least in my experience, the servos hold the position you asked for and the point stays changed!

Now you know what that push-button to the top right-hand of the mimic diagram is for.