Autopilot low voltage alarm

[stevensuf]

Main unit is a raymnarine type 300 computer with st600 display, i am getting a low voltage alarm and the pilot will do nothing, have checked power at input of course computer and its reading 12.8v so looks ok, swapped over st600 unit with a spare ,, still getting error of low voltage.

Does anyone know if the low voltage error is made by the ctype 300 computer or in the st600 or both? its hard to get into the seatalk connector at the st600 to check power there

[atoll]

well you have established it is not the st6000,so it is either the wiring or the course computer.

i would check the seatalk connection for voltage before suspecting the course computer.
once you have exhausted that possibility and you still have an error then think about replacing the type 300(worth checking ebay for these old units,about £300 for an unused one on ebay)

as a test ,run 3 wires direct from the 300 to the st 6000,bypassing the old wiring,just get the colour coding right,if you dont have some small spade terminals you can push the wire ends over the red ,grey and yellow terminals on the st6000,the 300has terminal block connections.

[stevensuf]

as luck would have it, well pre planning would have it , i have a spare type300 computer (ebay) have checked everything now, all showing 12.8v voltage into computer out of computer and at end of sea talk cable to st600 also 12.8v, will swap out the type 300 , maybe an internal fault? only thing left to do!

[noelex 77]

Yes it's probably an internal fault. These units are getting old, a bad transistor seems the most common fault.

However it's important to measure the voltage with the course computer running (or trying to start up). With a high resistance conection somewhere, the voltage reading will often be normal, untill you try to draw some current. if the voltage has dropped low during start up the course computer will shut down, draw very little current and the voltage can jump back to normal. Have someone watching the voltage as the autopilot starts.
This is probably what you did, but 12.8v is high when the autopilot will be drawing a few amps, so I thought it was worth checking.

[sailvayu]

Often a poor connection will show good voltage until you place a load on it then the resistance will cause the voltage to drop. Try turning the unit on and into auto pilot mode while watching the volt meter. Check the voltage at the drive unit as well as this could cause the computer to sense a fault as well. Good luck I know this type of thing can be frustrating. Check and clean all connections from source to unit as well.

[stevensuf]

The whole lot came on ok, but when i set the control to auto, the low voltage alarm would come on the screen, have swapped over the computer and all is working fine now, may have been a dodgy connection i could not see , might swap them back over later to see if the fault persists, but im 90% certain the computer was dodgy. now i need another back up!!!!