5V present on all of the 7i77 TB4 encoder Inputs

Hello guys, I have been a silent reader of this forum for a long time now, because all my upcoming questions were already answered.
Thanks for that!

My question:
On my TB4 of my 7i77, on all inputs, 5V are present, so the encoder signals just get lost. I first discovered this while moving the Y-axis by hand and the display of axis did not change. The Y-Axis is connected to the encoder 01 on TB3. At that point the X and Z encoders, also connected to TB3, did work just fine.
After some trial and error (unplugging all power supplies, 5 and 24V; disconnecting the PC; trying a new PNCconf machine; switching encoders around) it suddenly started working again. All encoders except the Spindle (encoder 05 on TB4) are single ended.

After getting the position control of XYZ to work, I wanted to add the C-axis. This is when I discovered that on all pins of TB4 5V are present (except the 3 ground pins of course)
This stays that way, regardless of encoders are plugged in or not. The 5V are there immediately when the external power supply is switched on. It does not matter if the 24V power supply or the PC are connected. Also opening linux cnc does not change anything.
Disconnecting everything except the external 5V brought no change either.
When measured across the 5V pin and an input pin on one encoder on TB4, i get a voltage difference of 0.15V. I am assuming this indicates that no direct short is present (at least i  hope so).
When only the PC is connected, i get around 1V on all pins of TB3 and 4. No difference between TB3 and TB4.
The jumpers on the 6i25 and the 7i77 and the 7i74 are set to external 5V power.
Since I got that same error on one encoder on TB3 and it disappeared again, i hope i did not destroy my 7i77. 

I'm glad for any thougts you might have.

Attached is a picture of my setup. I am working on a "Unplug only" conversion, so that during the conversion I can always go back to the Siemens control of my Hermle UWF600. 
 

5V is expected on all unconnected 7I77 encoder inputs as
all encoder inputs have a 2K pullup resistor to 5V.

This should be easily; overdriven by a TTL encoder output

Ok, thanks for that info.

Today I came back and discovered that the spindle encoder wasn’t plugged in. When plugged in the 5V dropped.
For the 4th axis this was not the case. Turns out this Siemens EXE board needed a separate enable signal before it starts working. Took some time to figure out...

Now all 4 axes work.
Now its time to get the homig to work.