HP Designjet T520 87.10 error

[elqueso666]

HI, I hope someone might be able to help me out with this issue.

I've had a 87.10 error before on a T520 series, replacing the encoder strip always cured the fault, but not his time.

The encoder has been replaced, still 87.10 error.

When turned on, the carriage moves all the way to the left but it's as though the carriage belt motor doesn't stop and keeps turning making a noise as the belt slips. 

The printer comes up with a carriage jam message, pressing ok causes the printer to move the carriage back to the right, service station moves, then the carriage returns to the left but stops under the control panel, returns to the right and comes up with the 87.10 error.

After replacing the encoder I thought maybe the belt had an issue (stretched?) so replaced it and the pulley, again with no success. I've made sure the shaft and carriage bearings are clean and lubricated, I ran the carriage servo test in customer support mode (can't enter the engineer mode due to the error) and it passes every time.

I wondered if anyone had any thoughts on what could be causing the issue?

Has anyone ever had the encoder sensor on the carriage itself cause an issue like this?

Many thanks in advance.

[Valsimot]

If I recall correctly the carriage motor when feels the resistance of the carriage reached the end should stop and rotate ( move) the back carriage to the right. Might be the motor or electronics. If it was an encoder sensor on a carriage then it would probably stop with an error earlier than reaching the left end. 

[elqueso666]

Thank you for your input Valsimot, it is a weird one. I thought the same about the encoder sensor on the carriage, do you know if there is ay way of testing the carriage motor as in the support meu the carriage test passes every time?