Looked at the machine issue again today and have come to the conclusion that perhaps a relay in the system is gone. It will be great if someone who has a syntec controller could verify my observations.
There are two switches on the Z axis, one is a rocker type with a roller at the end and it has two Bakelite wedges that depress it. The other is a proximity switch which has a metal leaf pin that activates it.
In the case of my machine, when the rocker switch is pressed at any point of its travel, the bottom movement of the Z axis is stopped and it can only move upwards. When the Z axis is at its maximum height, then the metal leaf goes over the proximity switch (which of course lights up in red), and its my opinion, that at that moment the proximity switch should activate the rocker switch to move the slide downwards and not upwards. This can be easily accomplished by a simple relay.
At the moment this is just theory, but if one of you could check this for me it will be great, by trying tiny movements with the jog dial to see if at the top, of the travel of the Z axis, if the rocker switch is pressed after the proximity switch switches on, whether its possible to move the slide up or only down. And similarly, at any intermediate position, if the rocker switch is pressed, if its possible to move the slide only up and not down.