About an older Siemens Simodrive 611

Hey guys,
First ever post here and first ever linuxcnc retrofit.
Just got a Chiron FZ12S Rapid CNC machine with a Siemens Sinumeric 810M controller and Siemens Simodrive 611 for all axis and spindle.
Sinumerik 810M is dead.

Started converting to Linuxcnc, got a Mesa 7i92 + 7i77 + 7i74 + 7i70 + 7i71.
Got the basics running. Home switches, XYZ motors running fine, drive enables, a few inputs conected and a few outputs conected (to allow for proper drive and machine start, it requires a complex sequence of relays and input feedback for the safety relays to activate)

Now i am facing the first issue. Basically i got the encoder feedback from the spindle going to the spindle drive and then to mesa 7i77 encoder 5 input.
I comand M3 S200 --> spindle rotates in right direction and at 200 rpm.
I then comand S1000 --> spindle drives jumps to 1000 rpm
If i comand M4 --> spindle rotates in the right direction and at the comanded speed.

Now the problem:
Up until 3900 rpm (spindle is 10500 rpm max) everything works perfect. If i comand S4000, encoder feedback seems to desapear and the drive goes to max rpm... It seems that the Siemens drive is disabling the encoder output to linuxcnc...
Drives uses +-10V and is in velocity control. 
Is there any way to say to linuxcnc that up to 3900 rpm it should use encoder feedback and after 3900 just use the index pulse from the encoder to control the rpm?

Thanks a lot guys and i will be posting pictures soon.

Also, what resolution is the encoder? (or simulated encoder output of the drive)

Resolution should be 2048 pulses per rev.
I will test the output of the drive to see if it changes the resolution when changing from 3900 rpm to 4000

This is all Original Wiring and was working with the old sinumerik

PCW wrote:

Also, what resolution is the encoder? (or simulated encoder output of the drive)

Here are some pics of the thing... I found this parameter (P033) on the Simodrive manual. it seems to turn off spindle encoder output after FW3.0?? I need to see what this means...
Is there any way to tell linuxcnc to run with encoder feedback until 3000 rpm and then turn off encoder feedback??
Maybe i can change the parameter on the drive to always output spindle encoder information....
Will keep you updated...

Today was a new day, i tested the ouput on the spindle drive itself and it seemed fine for the most part.. the only thing i found odd was the signals voltage... It showed an amplitude of 2.5 volts? from low state to high state...
I believe a real encoder conected directly to  the 7i77 would have 5 volt amplitude...
Will test this now.
The pictures show encoder output A on chanel 1 and output /A on chanell 2.

How would you go about changing parameters without the original control? It doesn't look like there is any way to manually do that.

The simodrive 611 is a bit old, most "parameters" are changed with resistors and potenciometers.
The drive for the spindle has a little display and you are able to Change parameters on it.

Reduced the encoder output from the spindle drive to half (2048 -> 1024) and got twice the speed... So my problem is that i AM reaching the encoder count limit of 2 MHz. 
I am Now trying to tell linuxcnc to use encoder only up to 2000 rpm and then just ignore feedback from the encoder.