I post an update as this information might help someone else with the same issue, again hopeful that someone will reply with further suggestions.

I removed the transformer from the Simplatron DCVT-2 Isolation card, it’s a Magnetix 120 -120V to 15-15V. A suitable replacement is a Vigortronix - VTX-120-003-615, 3VA 2 x 15V. The resistance of all four windings on the old transformer were checked against a new one and all were found to be correct. The original was soldered back onto the board.

I replaced the original R15 resistor (220 ohm 1W) with a 210 ohm 3W resistor.

I replaced the Bridge Rectifier (W02F) with a new one.

I replaced the Zener diodes D9 and D10 (BZX85C10V) with new ones.

Result - The components on the Simplatron board are now running much cooler, you can keep a finger on the resistor without it burning. Even though the speed of the spindle was still occasionally fluctuating I managed to cut 0.3mm deep in mild steel with a 5.5mm cutter for about 30 minutes. I thought I had fixed the problem but on the next machining operation the X,Y,Z stopped responding, the spindle continued spinning and the computer flagged - “Machine not responding’.

I changed the sole RIFA capacitor (0.15uF / 150nF) on the internal Lenze 534 board for a new one.

Result - This time I really though I had fixed the issue but after about 40 minutes of cutting the same steel the computer lost contact with the 260VMC (no on screen message this time) and after about 50 minutes X,Y,Z stopped responding and the spindle continued to spin.

I turned the ‘IxR compensation’ trimmer potentiometer on the Lenze 534 clockwise about 1/16 of a turn while cutting steel as above. I did this four times and spindle speed remained fairly consistent rising and falling a maximum of 40 rpm above the 2000rpn that was set.

After 1 hr 50 mins of cutting again I though ‘problem solved’ but just as the Z axis took a plunge cut the machine stopped responding on X,Y,Z but the spindle continued.


Ahhh…..

Any suggestions, please!