Fried my THCAD-10

I had a wiring fault that seems it put raw arc voltage on the THCAD-10 inputs and it may have broken something. The instructions say it can handle 500 volts indefinitely. I've never seen my plasma put out more than about 150 volts so it should have survived. I've got it set to 1/32 mode.

So I could do some diagnostics, I connected a 96 volt power supply to the internal plasma voltage divider and I'm getting 2.9 volts at the high voltage inputs which is what I expected. I see the flashing LED increase frequency but I'm not seeing any real change on the frequency outputs when I check it with my multimeter, I get 22-26 Khz which is nowhere near within the expected range.

I'll see if I can get my USB oscilloscope set up tomorrow in case my multimeter is faulty as its nothing special.

What worries me, I'm not seeing any rawcounts happening in the 7i76e encoder input using halshow. Could my 7i76e be damaged?

How can I test the thcad and the 7i76e encoder?

Even a temporary 1000 V input will not damage the THCAD-10, It sounds more likely that some kind of
fault generated excess voltage on the low voltage (un-isolated) side of the THCAD.

Probably the easiest way to check the 7I76E encoder inputs is to jumper the 7I76e encoder for TTL mode, "watch" the encoder A,B,Index inputs and ground them (TB3 pins 7,10,13) one at a time (to TB3.9) and see if the hal pin changes

You you probably need a 'scope to check that the THCAD outputs have proper voltage swing and frequency,

Rod

And I thought that I had a bad day on Saturday when I killed the Z axis driver on my table. So no new arc voltage testing got done.

Your plasma will put out up to about 340dc (240VAC*1.414=339.6vdc), it only very briefly does this normally on arc starting.

John

Thanks Peter (and John for consoling me too). I have been so careful with all of the electronics. I found some loose solder slag in one of the backshells I have opened too many times that I care to remember. chasing down faults due to poor plasma documentation. I think that is what caused the fault.

I'll do some tests today and report back.

Help me out here. Should I connect the Oscilloscope ground to the F- or -5V pin on the THCAD?

This does not look right.

This is with the probe attached to F+ and F- which I disconnected at the 7i76e end so I could hook a probe on easily.
I also tried F+ and -5V but it made no difference. The reading was still random as shown.
I'm assuming I should be seeing a sine or square wave.
I've still to test the 7i76e encoder.

You should connect your scope ground to the THCAD GND pin (P1 pin 6)
You should expect a ~ 3V square wave from the F+ and F- pins (in the DIV/32 mode)

PCW wrote:

You should connect your scope ground to the THCAD GND pin (P1 pin 6)
You should expect a ~ 3V square wave from the F+ and F- pins (in the DIV/32 mode)

Thanks Peter. Thats what I thought after I did these screen dumps. I tried it that way and did not go outside the 50 mV range. The board must be cactus. I'll go and grab another screen dump to be sure. Still need to test the encoder but I understand your instructions for that one.

Tommy, thanks, but my torch is a blow back start and is designed for CNC application so the high frequency start does not exist.
(internally in the torch, the arc is created by a short between +ve and -ve electrodes, then air pressure opens up the shorted electrodes and the arc transfers to the material). Everything on the machine is grounded properly back to a star ground and the plasma frame is earthed to an earth rod.