Electronics > Repair

How to repair/replace very old Microstepping drivers in Torcam CNC

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Langdon:
I have an old Torcam CNC router machine that contains 3 microstepping drivers by Tor Computerized Systems Inc.

There is one driver per axis.

It is controlled by a PC running LinuxCNC on Debian over a parallel port through a PMDX-122 breakout board.

The PC, the parallel port card, and the parallel port cable are reliable and fully functional.

The PMDX-122 board works without any problem.

However, the CNC Machine does not work.

I believe the microstepping driver is the problem. Its microcontroller relies on an EPROM chip that has likely become corrupted over the 30 years since the EPROM was written to.

Should I replace the drivers?

What should I replace them with?

The existing(broken) drivers use 2 L6203 full H-Bridge drivers and are definitely capable of delivering substantial current (6A), the replacement drivers also must be capable of delivering at least 6A (in total for both windings) .

The 2 L6203 H-Bridges from each microsteppping driver are still fully functional; should I just desolder them and make my own stepper driver board using the existing H-bridges and heatsink?

I have connected a smaller stepper motor to one of the microstepping drivers to test the driver and make sure the Router machines's motors are not at fault. However, the stepper motor i wired up does not move. While the stepper motor I am using to the the driver has 200steps/revolution, so it will take a lot of microsteps to move any noticeable amount, it doe not appear to move at all. The motor heats up and make a high-pitched noise, but it doe not move any measureable amount even after running it for 15 mins.

timeandfrequency:
Hello Langdon,

If you suspect the stepper controller/power stage to be defective, try to locate the STEP & DIR signals of one axis. Those should come from the computer.
Apart for very specific needs, it's too much work to developp your own microstepping power stage.
I would sugggest you to buy such a 7.2 A microstepping driver/power stage and try to wire it to one of the genuine axis motor.
https://www.omc-stepperonline.com/digital-stepper-driver-2-4-7-2a-18-80vac-or-36-110vdc-for-nema-34-motor-dm860t
The user manuel can be downloaded from the product page.
You should even be able to reuse the mill's genuine power supply when using these kind of power stages.

I also found this page about an update of the TORCAM CNC mill :
https://makebright.com/2014/11/torcam-cnc-mill-comes-alive-with-easelgrbl/

Swake:
1 driver dead, ok, but 3 drivers dead at ones sounds less probable. Could you share the brand and type of the drivers and the steppers?

You write that "The PMDX-122 board works without any problem", I assume you see the LED's blinking when you send some command in LinuxCNC. Have you been able to confirm with a scope or maybe a multimeter that the step and dir outputs of that board effectively output something on all axis towards the drivers?

As per the previous message make sure that the power supply for the drivers is within spec of those drivers.

Other things that might prevent correct functionality are the e-stop (emergency button) and homing switches. If these are not configured and wired correctly the board is never going to send something to the drivers. Cabling in general is actually rather sensitive on these parallel port setups.

Langdon:
I know the step and dir signals work.

The dir led turns on or off depending on the dir.

The step LED does not light or flash, however, that is because it flashes too fast to see.

If I wire up the step pin to a 4520B CMOS binary counter IC with LEDs connected to the outputs,  it counts reliably.

If I wire up the stepper driver's step pin to one of the counter's outputs, it still does not work.

Langdon:
The drivers are very old.
They say Copyright 1991 Tor Computerized Systems Inc. on them.

They could be 33 Years old.

I fear their EPROM chips might have degraded.
They were kept in a school that has no A/C for up to 32 hot summers, which could have accelerated their degradation.

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