Citizen L20 Zero Return issue

[Superfly33]

Greetings all. Can anyone offer any info as to why I have to perform the zero return operation on every axis except the main spindle (Z axis) every time the machine has powered down? There was also a servo warning flashing up on the back spindle x axis which I've got rid of with a spot of rewiring but the zero return issue remains.
All the switches are ok, and the wiring all appears ok. I've checked for continuity along each of the looms and no obvious breaks are showing.
Cheers
Mr Superfly33, not so super at the mo.

[onthebumper]

I would say the battery voltage is too low but generally there is more then one battery pack on that machine. You can still check it out to see if they are ok. They should be labeled MDS-A-BT# and should measure around 3.6v.

Beyond that it is difficult to trouble shoot. There could be a short or coolant in one of the cables which is shorting the battery wires and dragging the voltage down. It could be a bad encoder that is doing the same thing.

Do you only have to perform the zero return in the morning when it has been powered off for an extended period of time or anytime you power it down. If it is for an extended period of time then it points to the data in the encoder being lost because the battery voltage dropped to low.

[MikeMc]

I believe if the batteries were low, you would get the battery alarm as well. It will make a differance which model L20 (L5 or L7 or ?) as they have different controls, etc.

[Superfly33]

Thanks for the responses all. The back up batteries are showing 4.5volts. Both sets. The symptoms are changing all the time now. Sometimes only spindle 2 needs zero returning, and sometimes other combinations of every machine axis, but always including x and z on the back spindle.
As regards time spent powered down, overnight or a quick on/ off throws the problem up. Up to now it's been fine providing it wasn't powered down.
However...
To further compound the problem it is now randomly changing the diameters during the program cycle. The tool post seems to be forgetting it's position and moving up or down by anything up to a couple of mm.
General consensus is pointing to a wiring issue. A good couple of days with my head in it have unearthed nothing yet. The usual broken brittle oil damaged wire has yet to reveal itself on this occasion.
I shall continue swearing a lot and throwing tools around!

[MikeMc]

This is why its good to have some spare cables around, or a second machine that you can swap with. In my mind, I would look closely at the main cable running into the sub spindle smart servo. I had one of those come loose once, and was almost at the point of falling off when I started getting alarms. To troubleshoot, just turn the machine on with no alarms, and start wiggling cables. Don't laugh...it works if you have a wire going to ground.

[onthebumper]

I ran into a Citizen years ago that had similar issues with having to zero return all the time. The problem seemed to move from axis to axis if I remember correctly. Mile had a good question before, what type of control do you have on this machine? The one I worked on was a 500 control and it turned out the MCU board in the control was the problem. This board controls all movement on the machine so it would point to your accuracy problems as well. You might benefit from giving Mitsubishi Service a call. They might have a couple of good pointers for you to check out. It can't hurt to call. 847-478-2500