All,
On my Series II, BOSS 6 machine I lost Z-Axis movement!!! Can some one please help! It was running fine, but in the program I overtraveled the quill. Now I get no movement in jog. I was able to move it off the limits by holding in the limit overide, but now when you hold down jog, the drive motor "twitches" a little, then sounds like its spooling up, but the belt does not turn and obviously the quill does not move up... Any ideas??!!

Did you check if the motor shaft was turning? you may have sheared a pin or key on the pulley.
Al.

Yeah, no motion on the motor shaft... The drive pulley is still frimly attached... I pulled the belt off the motor to take load off the mottor and still nothing. It "twitches" a bit, then holding the jog + it sounds like the motor is spinning, but its not...

Let me add to this. With a programmed feed rate on "Z" it willl move. It just will not rapid....

Well let me subtract. Seemed to work.. not the case...

Sounds like a borderline bad transistor in the final drive stage.

George

I thought something along that lines. This would be one of the 4 transistors on the Z-Axis drive board?? I swapped that board out with a known good one and still have the issue...

Yes but did you drop any of those tiny washers or screws? I cannot tell you how many times I found one of those laying across 2 terminals on that side door. Check carefully the terminal strip at the very bottom and the board with the 12 diodes.

George

Yeah, checked to see if anything dropped. All is clear... Any other suggestions?? Really frustrated with this...

Which board have you replaced, the printed circuit board or the aluminium channel with 4 Transistors attached.
I think machintek is on about the aluminium channel one but if you've changed that try changing the printed circuit board (SMD) one with one off another axis. Also you could try flipping the ACC printed circuit board and see if the problem moves on to the X axis.

Chris

Something else to try. Attach a meter to the base of each Z transistor (one at a time) and set it to DCvolts. Put the machine in step and step each transistor at least 4 times. They should turn on and off crisply. If you have a bad diode on that board on the bottom right of the side door, one transistor will be off, turn on half way, turn on fully, turn off half way, You may or may not have this problem. This has happened to me only a few times in 25 years. But it can cuase symtoms such as yours.
Another very remote possibility is a flaky optocoupler on the output of the ZDI. I had one machine do this. It sends the commands to the SMD.

George

As you all said, it was a transistor. Appreciate all your help!!