Kanalog DAC3 pushing constantly 11VDC

[Jykke]

Hi, new in the forum.
We have made modernization project for a 80's Sigma MC6 / 800. The project went pretty good and the machine has been running couple months now. Small optimizations has been done and we are still learning how to work with "modern" CNC software and G-code.

Anyway we have a problem now. One of Kanalog DACS (DAC3) is pushing constantly 10,99VDC out even if there is no request to move or channel active. Our setup is that DAC3 is controlling the spindle motor (Servomac 2570 + 112 NL). Any idea what could cause this error. What kind of protection do you suggest to protect other DACS or could it be just faulty Kanalog PCB? We are now using DAC4 for the spindle, but we don't want to this happen again. Too much RPM for a old piece of hardware..

[TomKerekes]

Hi,

11V should not be possible from software so that would indicate hardware damage. But to check if you Flash "New Version" to make sure KFLOP is in its default state. Then cycle power without doing anything else does DAC 3 measure 11V? What does the Analog Screen indicate?

Any contamination on Kanalog?

Maybe an induced voltage spike?

How is your Spindle controlled? Is there any feedback to know what it is doing? ie an encoder?

[Jykke]

Analog screen shows normal controlled values and 11V stays in DAC3 even if you power cycle or re-flash the board.
I have to check the Kanalog board, but probably reason is voltage spike or faulty component on the Kanalog board. Any idea can the DAC components replace easily by soldering or do you recommend just order new board.

The guy who helped us to do this modification says:
"Spindle servo driver is controlled by analog differential velocity signal, we use ADC and ground to drive the spindle. There is a relay enabling the spindle signal to spindle driver, default state is the differential signals are short circuited by relay latches. Spindle is enabled with this relay. Spindle has tachometer, tachometer provides differential analog output to servo driver. Tachometer this is used as reference for primary servo loop. We have no encoder on this spindle."

[TomKerekes]

Hi,

I have to check the Kanalog board, but probably reason is voltage spike or faulty component on the Kanalog board. Any idea can the DAC components replace easily by soldering or do you recommend just order new board.

We recommend ordering a new board. All things considered we don't find it cost effective to repair boards.

Since everything else appears to be working I would expect the problem to be with the DAC3 output amplifier. U22 which is a TL074CDR quad op amp. If you want to attempt a repair on your own.

"Spindle servo driver is controlled by analog differential velocity signal, we use ADC and ground to drive the spindle. There is a relay enabling the spindle signal to spindle driver, default state is the differential signals are short circuited by relay latches. Spindle is enabled with this relay.

This seems strange to short out the Kanalog DAC? The TL074CDR quad op amp has continuous short circuit protection but I still don't think it is a good idea. You might add a 1K Ohm series resistor in this case to limit current. If the input impedance of the drive is very high this shouldn't add much error.

Spindle has tachometer, tachometer provides differential analog output to servo driver. Tachometer this is used as reference for primary servo loop. We have no encoder on this spindle."

Possibly the Spindle drive has some fault output, over current or something, that could detect a sudden full voltage command calling for a huge current/acceleration?