7i77 encoders not working

Most encoder issues we have seen tend to be wiring issues.
Marginal signals (due to wiring or wrong encoder type)
may work on some inputs and not others.

Mux issues tend to cause obvious even/odd troubles

A bad 5I25 or 7I77 is possible but of course all 7I77 encoder inputs
are tested and all 5I25 I/O pins are tested so if either are bad its something
that changed since shipping

I am unaware of any software issues with the encoders

I measured the voltage between A and /A on x axis encoder going to enc0 and voltage is 0.2 to 0.6 volts. Same for B and /B. You are going to tell me the wiring is wrong. I double and triple check wiring. According to original schematics I have encoder wire A going to A, encoder wire /A to /A, etc. Maybe original schematics are wrong, but how do i tell what is right? Is a way to test encoder wiring? I also see what someone told me was pull up resistor going between A and 5v, B and 5V, and index and 5v. Could that cause problem? If wiring is wrong, how come enc0 and enc5 work? Very confused. Help would be appreciated.

Are you sure your encoders have differential outputs?

It sounds like either they

1. Dont have differential (line driver) outputs (they are TTL single ended encoders)
2. They are not powered properly

You might check the voltages without being connected to the 7I77 (and its differential termination)

The encoders are
OPTcoder
Sumtak LBL-010-500
DC 5V 160 mA
8901-0039 500 p/r

wiring is:
8 5V
7 0V
1 A
3 B
6 Z
9 Shield
2 Anot
4 Bnot
5 Znot


here is website and pic of my encoder www.galco.com/repair/Sumtak-Daido/LBL-010-500
I was told they were differential, but not sure. They only get power from the enc0 connector and it is at 4.96 vdc.

Do not know how to check voltage if encoder is not connected to 7i77 because no other wires with power connect to encoder. Do you mean disconnect only A and /A and B and /B, and then check their voltage?

Still come back to same question -- why they work on enc0 and enc5? Can enc0 and enc5 be more sensitive to pick up low voltage signal and enc1 - 4 not able to see low voltage?

thx for help.

I would try with the 7I77 jumpered for TTL and with the /A, /B,/Z disconnected
(since they look to be TTL encoders not differential)

I would then check that you have close to 5V swing on A,B,Z when in TTL mode

The reason some channels work is that you signals are wrong and just barely large enough to overcome
the hysteresis of the inputs

If they were working, you would expect at least 2V (more likely 3 or 4V)
in one state and -2V (again more likely -3 or -4V) in the other state
measured across A and /A, B and /B and Z and /Z

You should really point your efforts at finding the issue and stop asking why some work and some do not.
Start by switching places, that should have been the first thing to do, connect the now working enc0 to enc1 input and see if it works, if it does check the encoder, not the card (7i77).
As i read the thread form the beginning, i have a feeling you have the enc1,2,3,4 supply reversed.
I would advise you check the polarity of said encoders on both sides, before you proceed any further.