ST 4000 Autopilot No display Constant Alarm

[white2236]

Just bought a new (to me) 1994 Hunter Legend 35.5 That has an Autohelm ST 4000. When I turn on the breaker I get no Display and the Alarm comes on. Previous owner thinks there is a reset switch but I cannot find it. I looked at the schematic and see no reset input and it must have 12Vdc because the alarm is working. Any suggestions (other then slams on Hunters and "buy a new Autopilot system) would be appreciated.

 

[kloudie1]

doesn't sound too good, but first, check those tiny slip-on, spade connections on the back of the instrument. Those can get loose and they can corrode. Sometimes they can be assembled incorrectly with the spade not inserted into the slot. The insulating cover might hold some connection between the spade and slot, but not a very good one.
Sometimes you can find stuff on E-Bay since Raymarine does not make the parts any more. Careful with selection because the newer "control heads" are purely a display and keypad while the 4000 units have the computer and stuff in the display head.

 

[white2236]

Thanks Koudie1, I have had it out and the connectors look good. Schematic calls out an 8A fuse but that looks like it goes to the servo and the display should come on without it.

 

[white2236]

Here is the service Manual if anyone else needs a Schematic.

 

[DougM]

Bear in mind that though the connecters look good, you could easily have a broken wire at the point where it enters the spade connecter itself, or even further back in the wire.

 

[white2236]

Bear in mind that though the connecters look good, you could easily have a broken wire at the point where it enters the spade connecter itself, or even further back in the wire.

Thanks dougm

 

[white2236]

Update. I opened the controller and there had been an inch of water that had dried and left a bunch of corrosion on the curciut board. After cleaning it I noticed the resonator leads had corroded through. What an ordeal to find that part. 11Mhz is not a common frequency. I had to buy 5 so I have 4 left if anyone needs 1.