Debugging joint amplifier fault

No 5V driver can supply 5V to a load (it will always have some internal resistance)
You might check the drive input resistance between STEP+ and STEP-
when unconnected. If both drives match then its likely that 7I76E S/D
outputs have been damaged.

Note, when checking the S/D outputs, its  much better to measure both
the STEP+ and STEP-  pins individually relative to ground

Actually I was wrong; the servo specs provide some more detail about the required pulse signal.



So >= 3.5V is acceptable, which explains why it works on the channel with 3.7V vs the one with 2.4V.

Still none the wiser about why the voltage drop is so large on this servo.

I measured the resistance earlier, but wasn't sure if doing that unconnected would be too naive. The measured resistance was 3.7 Ohms between step+ and step on both, the good and the bad servo. Both servos were disconnected completely from power and from the MESA card.

I'll measure the signals individually to ground.

Measuring to ground I get results between 0.3V on step- and 3.2 on step+, on both channels. Not sure what to make of these measurements...

Just when I was about to give up and just risk working with the swapped servos, the second servo now shows the same symptoms when running on the bad channel .

So it looks like it is the 7i76e that broke and not the servos .

Plus, that card seems to be still not in stock anywhere in the EU. Already had that problem when searching for one two years ago.

At least I am only using 4 of the 5 channels, so was able to reconfigure the machine the unused channel instead, hopefully I'll find a new card, soon.

Thanks a lot for all your help, PCW!