Test LinuxCNC without motors and encoders connected

I will connect the 7i77 to external 5V later, but on my test bench I only have one power supply available, and this one is set to 7V and used for field power

The encoders have 8 wires, and have the +, -, A, A/, B, B/, Z and Z/ outputs. In the documentation of the encoder I could read that it are incremental encoders. But I'm not sure about that... (Hohner BS192/500)

The jumpers on the 7i77 are in the right hand position, and that is in the Differential position.

Most differential encoders output 5V signals regardless of power supply

You can verify operation by measuring across the pairs
(from A to /A etc)

You should always measure a voltage above 2V absolute across the pairs
(greater than +- 2V in all states) when connected to the 7I77,
That is, one state should be +2 to +5V and the other -2 to -5V but never any voltahe less than +-2V

I have 0.87v between pin 1 and 2. So I think the encoder is not working by 4.7V (sometimes it works for a few minutes, but unpredictable)

Is there a difference between incremental and differential encoders?

You can try 5V, but I would expect the trouble is elsewhere
(actually even 0.87V differential should work but anything less than about 2V indicates a line driver issue)

Do you have link to the encoder manual?

This is all I could find.
The encoder is a Hohner BS193/500

As far as I can tell that's the LD5-12 option

Do you get both 0.87 and -0.87 if you wiggle the motor shaft so you get both states?
Do all encoders act the same?

I have 0.87, even when i wiggle the shaft in both ways.
And I only have one encoder dismounted from the CNC machine.
But I'm pretty sure that the encoder is still working.
I've started the CNC just before the dismounting, and it was working fine.

What does LD5-12 means ?

As far as I could understand the encoder signal mode was 9 = LD5-12 (probably line driver 5-12)

I would verify your wiring, perhaps just supplying 5V to the encoder and checking the unconnected output pins

Ok, I've done a test. I've disconnected the encoder from the 7i77
When I supply 5V to the encoder, I measure 3.7V on the output pins
When I turn the encoder, the value changes.
By 10V, I get 8.7V and by 4.7V there's 3.2V on the outputs.

Then I used the onboard 4.7V, and the output was also 3.2V.
But when the outputs are connected to the 7i77, there's 0.87V

If (with 5V power) you measure across A, /A, is the voltage +3.2V in one state and
-3.2 in the other state?

If not, the outputs are not differential