7i77 encoder input problems ?

Hello,
today I had an interesting issue with one of the 77 boards we use .
The y axis(enc 1) stopped reading position . I moved it over to enc 4 input and it started working normally .
Has anybody had that issue ?
Any suggestion on how to avoid this, as that's the second time I've had that happen ?

Cheers

consider a Bigger elco around 2200uF right bevor the encoders Voltige there seams to be a Slight difference to encount and the encoder stops

I would check that the 5V is OK and that the input is jumpered properly for the type of encoder (TTL or differential)

The 7I77 encoder inputs are fairly rugged, accepting transient voltages of up to +-25 V without damage, but problems like missing grounds on motors can generate transients greater than 25V, so you might want to check the encoder signals with a oscilloscope

You can check individual encoder input pins by

1. Jumpering the encoder input for TTL mode and disconnecting the encoder

2. Watching the encoder input a,b,index pins with halshow
the pins will be named
hm2_card.0.encoder.01.input-a
hm2_card.0.encoder.01.input-b
hm2_card.0.encoder.01.input-index
where card is the FPGA card name

3. grounding the encoder+ input pins at the 7I77
The watched pins should change state when grounded

Thing is this is on a machine that has more than a year of use on linuxcnc .
The boards don't interface the encoders directly but from an encoder buffer in the servo drive . I know the signal from the servo is good since input 3 reads it fine .
I'll check it with a scope tomorrow just in case .