Rudder reference unit intermittent failure

[jjorio]

Hello everyone,

Got an intermittent failure of the rudder reference unit, and I'm trying to find the fault.
Being intermittent I figured a connexion problem, but can't found any at the moment.

I disconnected the unit, to test the resistances, as specified par Raymarine or other members :
Red to Green, steady 7.03 K
Red to Blue, 2.32K to 4.85K, when turned from one side to the other. Midship value : 3.65K
Green to Blue, 2.47K to 5.06K, when turned from one side to the other. Midship value : 3.75K

I know these are not the values expected by the test, but appart that they are offset, the values are centered properly, and vary correctly with the arm turn.
Also, I dismantled the unit and the pot is : Vishay Spectrol 357-4158-502. There is also a 0939 written on the label.

My question is :
- Can the unit work with these offset values ?
- Is the pot clearly the problem ? in this case, where can I find one for replacement ?

Of course, I read all related posts I found in the forum

Thank you everyone,
Cheers,
Jaad

 

[jiris]

It is almost certainly the pot. What makes the manufacturers using pots with friction pick-up that is absolutely certain to fail only god knows. As the rudder is practically in constant motion, the situation call for either optical, inductive or capacitance sensor that is not subject to mechanical wear. Beats me...
Anyway, the original replacement sensors cost usually around $200 - quite a sum for what is, in most cases, just a 5k pot. Some more sophisticated are running in oil bath what is supposed them to last longer. It is definitely worth looking for some third-party source. I replaced the rudder sensor on my Raymarine ST6000 about 3 years ago by a high quality pot for $30 - made of all countries, in Slovakia. The manufacturer guarantees 500,000 turns lifespan, what sounds reasonable and the thing is still working no problems. Unfortunately, can't remember where I bought it, but if you check with some general electronics suppliers, you will find something similar for sure.

 

[RichardS]

Of course, I read all related posts I found in the forum

Thank you everyone,
Cheers,
Jaad

Some of the previous threads suggest places to buy a 5K linear pot. The original pot is apparently specific to Raymarine so you might need to buy a pot with a longer shaft and cut it down.

Richard