Simrad autopilot question

[Wdeertz]

I have a simrad autopilot depicted as the following simnet network. It’s been working fine for the past 4 years since I’ve owned the boat. Recently while underway the autopilot went blank (no heading shown) and stopped working. While looking under the service menu I noticed many nmea transmission errors. I disconnected the backbone cable going to the flybridge unit and placed the terminator here. The AP28 headunit worked perfectly with no nmea transmission errors. I removed the flybridge AP24 headunit and connected in place of the AP28 at the lower helm and the autopilot worked perfectly so I think I can rule out the AP24 unit is bad. I then connected the AP24 unit at the lower helm in place of the 6m backbone cable going to the flybridge and put the terminator in the 2nd connection on the AP24. With both headunits on the autopilot seems to be working fine with no nmea network transmission errors. As such I’m surmising the 6m cable going to the flybridge has gone bad. Any ideas how a nmea cable fully enclosed in a wire chase could go bad? Possibly chafing somewhere along the cable?

Is there an easy way to test that cable before I go to the effort of replacing? I was thinking of jumping the connectors with a wire to test continuity and resistance, what sort of resistance should it read? Thanks

 

[tiltrider1]

I have had T connectors go bad. Try swapping a known good T with the first T after the cable. It could also be the T that the cable is plugged into. Anyway, I would rule out the T’s before I dragged a new cable through the boat.

 

[Wdeertz]

I have had T connectors go bad. Try swapping a known good T with the first T after the cable. It could also be the T that the cable is plugged into. Anyway, I would rule out the T’s before I dragged a new cable through the boat.

Thanks for the suggestion, I should have mentioned in the original post I tried connecting the 6m cable going to the flybridge directly to the AP24 (thereby taking the 3 way joiner out of the equation) with a resistor in the other connection and still got NMEA transmission errors. As far as I can decipher from reading the simnet documentation I should be able to connect directly to the AP24 without the joiner on the flybridge. I know the 7 position joiner is good as everything on the lower helm work fine. Am I correct in my understanding?

 

[tiltrider1]

Got it. Get another cable but perform the same test. If you get different results between the two cables you will have found your answer.

Just trying to save you the effort of pulling a cable only to discover it’s not the issue.

 

[Wdeertz]

Got it. Get another cable but perform the same test. If you get different results between the two cables you will have found your answer.

Just trying to save you the effort of pulling a cable only to discover it’s not the issue.

Good suggestion, I don’t have a spare 6m cable so will order one and try it before running to the flybridge. The only thing I can think of is that cable got pinched somewhere and started causing network errors.

 

[JP2]

Gyro compass issue??

 

[Wdeertz]

Gyro compass issue??

I’ve narrowed down the issue to the long cable going to the flybridge. Works fine with this leg disconnected so must be pinched somewhere along that run. Have ordered a new cable.

 

[Duvie]

I have a simrad autopilot depicted as the following simnet network. It’s been working fine for the past 4 years since I’ve owned the boat. Recently while underway the autopilot went blank (no heading shown) and stopped working. While looking under the service menu I noticed many nmea transmission errors. I disconnected the backbone cable going to the flybridge unit and placed the terminator here. The AP28 headunit worked perfectly with no nmea transmission errors. I removed the flybridge AP24 headunit and connected in place of the AP28 at the lower helm and the autopilot worked perfectly so I think I can rule out the AP24 unit is bad. I then connected the AP24 unit at the lower helm in place of the 6m backbone cable going to the flybridge and put the terminator in the 2nd connection on the AP24. With both headunits on the autopilot seems to be working fine with no nmea network transmission errors. As such I’m surmising the 6m cable going to the flybridge has gone bad. Any ideas how a nmea cable fully enclosed in a wire chase could go bad? Possibly chafing somewhere along the cable?

Is there an easy way to test that cable before I go to the effort of replacing? I was thinking of jumping the connectors with a wire to test continuity and resistance, what sort of resistance should it read? Thanks

MICE during layup??

 

[Wdeertz]

MICE during layup??

Doubtful as the boats been in continuous use the past 4 years. The wire chase is very tight with wires so I’m guessing the cable got pinched somewhere along the run.