I知 hopeful that someone on this forum can help me to get my Boxford 260VMC running again.

Since acquiring the machine about three years ago it has run faultlessly using the original Boxford software so I hope to get it working again as it was. I知 not currently considering upgrading the machine to run under Mach 3/4 / LinuxCNC - these options may need to be considered later!

The problem -

After a few minutes of use the spindle speed begins to fluctuate, sometimes dropping by up to 200 rpm from the programmed value and then within a second or so recovering again. After several minutes of spindle speed fluctuations all movement on the X, Y, and Z axes stop, the computer hangs but the spindle continues to spin until the 260VMC is switched off at the wall socket. Once all movement of the X, Y and Z axes has stopped the spindle appears to run without spindle speed fluctuations indefinitely if left. The slotted opto switches / spindle encoder have been checked / cleaned and look good.

Observations -

Two components on the Simplatron / Simplatroll DCVT-2 Isolation card (fixed to the end of the Lenze 534 speed controller) get far too hot to touch. These are (T1) the 0 - 120v 0 -120v 0 - 15v 0 - 15v 3VA transformer and (R15) a Red Brown Brown high power resistor.

The board has been removed from the machine and scorch marks are visible next to the pads for R15 but also, to a lesser extent, the pads for D9 and R10.

Due to the apparent overheating of components on Simplatron isolation board I am thinking that this might be causing the spindle speed fluctuations and will begin replacing components if others on the forum agree.

Questions -

Has anyone experienced the same problem and can they share a solution?

Does anyone have a circuit diagram / component list for the Simplatron DCVT- board and any guidance on what it does / how it works?

Am I right in thinking that the Boxford control boards supply a 0 -10v PWM signal to pin 4 of the isolation card with the mark / space varying for different desired spindle speeds?

Does the Simplatron isolation card then change this PWM signal into a 0 - 10V analogue signal input to Pin 8 of the Lenze 534 speed controller which then adds it 110v?

Are there any suggestions for alternative, straight swap isolation cards I could use to replace the Simplatron DCVT-2 if changing components does not fix the issue.

Many thanks in anticipation.

Mike