Stanko SMO 32 CNC - problem with limit switches

Hi,

I bought an old russian milling machine with Heidenhain TNC 360 and it looks very similar to Maho E and E2 series.

In the future I want to retrofit it, but for now I wanted to make it work as is to figure out the state of the machine (cause maybe if some stuff is worn I will also want to replace it before or while retrofitting).

The only problem that I found so far is with the Z axis limit switches. When I power on the machine I need to move all the axes to find the reference points. In this mode I can move the Z axis all the way up and all the way down. The problem is that after I get the reference points most of the time I can't move the Z axis up anymore. And I write "most of the time", cause from time to time it worked OK and I was able to move the Z axis up. Here is a video showing the situation: www.dropbox.com/s/n1g2pqotjgerdl6/video_...27_16-59-21.mp4?dl=0

I suspect that one of a few things may be happening here:

1. There's some kind of a disconnect on the limit switch for the Z axis. It seems possible, but I also don't really understand why would it work in the "reference points mode" and not later on?
2. There's a problem with the Z axis motor, like maybe the brushes are worn out and it works when moving the table down, cause it doesn't need almost any torque and then it's problematic in up mode. That maybe could also explain the difference between the "reference points mode" and manual mode, ie. maybe for some reason the current is not checked during the former. Another question then would be if the message wouldn't be different. It says "Endschalter" on the screen, which means a limit switch. I'm not sure if it would say anything different if the problem was with the torque.
3. The limit switch itself (ie. the hardware part) is somehow faulty. This case also doesn't make sense with the difference between two modes.

Any ideas? I will probably try to dismantle the front side at some point soon, but before I dig too deep I wanted to ask for opinions of more experienced folks.

Maybe your hardlimt switch is broken and in Ref mode this switch not checked in control. This could be a reason why refmode working. For hardlimit take a look in wiring diagram if you have.
Or the message could mean softlimit. After refmode your scale is adjust. Maybe wrong. On heidenhain control you have to press MOD and enter keycode for diagnostic paramter. I remember 123 is code to check user paramter. But first open cover and check how far you from end axis away.

Sorry to necro post, but I have this same machine. I'm based in St. Neots near Cambridge. (Machine is in a shed in Lincolnshire though).

Feel free to contact me if you wanted to chat about the machine. Did you get it working ok?

Mine is still running Heidenhain TNC355 (assuming my recent control repair gets it going again!)