7i76e Stepgen problem

Hi,

I'm having a problem with stepgen3. All other step generators work fine with my ihsv57 servo. I'm quite sure that the problems is not in the servo wiring or settings. I measured the voltages on stepgen4 and got 5v for step and dir+, and 0v for step and dir- when linux cnc is off, and when linux cnc is on, its the other way round.

But for stepgen 0, 1, 2 and 3 i get 0v for step and dir+, and 20-60mv for step dir-, whether linux cnc is on or off it doesn't affect the voltages. and all the stepgens can move the servo except stepgen3. What could cause this?

Sounds like the driver for STEP0+ .. STEP3+ (74ACT541 U19)
is damaged.

Thought I was careful installing it. Is this the part? TSSOP-20 package?

Yes TSSOP-20

I changed the U19 chip but voltages are still the same.

Now when I measured Vcc on U19 is 5v.

For stepgen 0 to 3 dir- and step- is 20 to 60mV, dir+ and step+ 0V.

For stepgen 4 step- and dir- 0V, step+ and dir+ 5V.

I didn't connect anything on the board after changing the chip except power and Ethernet cable. Could there be some other issue than U19?

If you connected say 24V to the step/dir pins, you may have
blown up the 27 ohm resistor networks between U19 and the
terminal blocks.

Thanks. Those resistor networks are RN3, 7, 24 and 32? What packages are those? I will try to measure the voltages from the U19 directly and if it's ok then I will change those resistors.

Yes RN3,7,24,32 27 Ohm MNR14 (1206)