B-737 SP-77 Autopilot

[sparkfarmer]

Hope someone can help!

We are an approved TC Aircraft Engineering Organization and,

I am installing a new Flight Management System in an older Boeing B737-200 jetliner. The 737 uses the Honeywell SP-77 autopilot. The SP-77 autopilot was fairly advanced for its day in that it calculated roll rate corrections based on aircraft speed.

My problem:
The new Flight Management System (FMS)also calculates roll rate corrections based on aircraft speed, so if I feed the roll steering output of the FMS into the autopilot (SP-77) without any other changes, then both units will apply a correction for speed, and the aircraft will turn too slowly and miss it's intended track.
How do I disable the Q-pot portion of the SP-77 input so that the SP-77 will ignore it's internal speed programming.

 

[aviat]

Isn't the SP-77 a Sperry autopilot?
Regardless, the best people to answer your question will be the people who made the system. They should be providing the wiring diagrams that you are using for installation. Below is a link to Honeywell's customer service

https://www.avionicservices.com/home.jsp

 

[sparkfarmer]

I agree. However the manufacturer of the autopilot does not wish to release this information as we are not installing a Honeywell FMS.

 

[kontiki99]

Maybe you can find something in the CMM for the autopilot.

Possibly there is an ARINC spec that defines the standard set of programming straps for the autopilot?