Autohelm ST60 Wind issues

GHA said:
Sounds weird, bet that got your attention!
I've never felt 12v even with wet hands - anyone know it's possible?
Click to expand...
It certainly did particularly that was was trying to steer the boat down wind in 45-50kts whilst trying to deploy a series drogue, singlehanded, in the dark, whilst getting random shocks whenever I touched something metal!
 
So I took down the masthead instrument and soldered it directly the wiring at the junction box wires at the bow wok of the mast. Readings were still the same so presumably the fault is unlikely the cabling in the mast or the masthead connector.

I’ve been unable to remove to circuit board to visually inspect any damage inside the instrument but the top part of the circuit board appears clean and undamaged.

Is there a test to the voltages in the cables without the instrument attached which would tell me if the voltages being sent are correct.

With no masthead instrument, the readings at the foot of the mast are:

Red to screen, blue & green
= 7.8v

Red to yellow
=0.2v

Screen to yellow
= 5v

Yellow to blue
= 5v

Yellow to green
= 5v

Screen to blue & green
= 0v
 
northcave said:
So I took down the masthead instrument and soldered it directly the wiring at the junction box wires at the bow wok of the mast. Readings were still the same so presumably the fault is unlikely the cabling in the mast or the masthead connector.

I’ve been unable to remove to circuit board to visually inspect any damage inside the instrument but the top part of the circuit board appears clean and undamaged.

Is there a test to the voltages in the cables without the instrument attached which would tell me if the voltages being sent are correct.

With no masthead instrument, the readings at the foot of the mast are:

Red to screen, blue & green
= 7.8v

Red to yellow
=0.2v

Screen to yellow
= 5v

Yellow to blue
= 5v

Yellow to green
= 5v

Screen to blue & green
= 0v
Click to expand...
I don't understand.

The voltage from red to shield is correct as that is the voltage coming from the ST60 display head which it is sending up the cable to the mast head unit. The MHU then uses this voltage in its circuit and converts it to a lower voltage coming down the yellow, green and blue wires. The voltage coming down these wires depends on the rotating speed of the cups (yellow) and position of the direction pointer (green and blue).

If you have removed the MHU, as I have understood, then surely the 7.8V is going up the red wire but as that is not connected to anything at the top then no voltage can be coming back down. Screen to the three other colours is particularly clear and must be zero if there is no MHU, If screen to yellow is 5V then something must surely be shorting out in the cabling or the display unit.

Richard
 
I’ve now removed the MHU and the cabling up the mast and taken reading purely at the junction box at the foot of the mast.

Screen/Red: 7.8v
Red/Blue: 7.8v
Red/Green: 7.8v
Red/Yellow: 0v
Screen/Blue & Green: 0v
Yellow/Blue & Green: 5v
Screen/Yellow: 5v

As you say there is clearly something shorting before it gets up to the MHU.
 
RichardS said:
I don't understand.

The voltage from red to shield is correct as that is the voltage coming from the ST60 display head which it is sending up the cable to the mast head unit. The MHU then uses this voltage in its circuit and converts it to a lower voltage coming down the yellow, green and blue wires. The voltage coming down these wires depends on the rotating speed of the cups (yellow) and position of the direction pointer (green and blue).

If you have removed the MHU, as I have understood, then surely the 7.8V is going up the red wire but as that is not connected to anything at the top then no voltage can be coming back down. Screen to the three other colours is particularly clear and must be zero if there is no MHU, If screen to yellow is 5V then something must surely be shorting out in the cabling or the display unit.

Richard
Click to expand...

ok so based on your pointers I went to the back of the ST60 wind instrument and pulled out the socket which feeds the MHU at the top of the mast. As you say, it should feed 8v to the MHU and therefore any readings directly out of the back of the ST60 Wind instrument should only read 8v at Red to Screen since all the others are receiving a signal back.

The voltages from the back of the instrument are as I mentioned above. Ita getting 7.8v on Red / Blue and Red / Green.

So this would say the unit is faulty and feeding bad signal up wires that should be receiving signals back from the MHU. So I tried a spare ST60 unit and that did the same. I then tried a third and also the same. Surely all three of my spares aren’t faulty.

Are sure about voltages I’ve taken with no MHU attached?
 
northcave said:
Is there a test to the voltages in the cables without the instrument attached which would tell me if the voltages being sent are correct.
Click to expand...

I believe there is a test procedure for this in the service manual; someone’s posted extracts from it here before. As far as I remember it sends sine waves out of phase with each other, so it’s not just a case of measuring voltages. I don’t have the manual to tell you anything more.

Pete
 
prv said:
I’m not an electronics expert but it doesn’t seem that surprising to me that the inputs would be somewhat close to ground.

Pete
Click to expand...
You mean and therefore it’s not surprising that the voltage reads close to 8v when I check the inputs against the red power wire?
 
northcave said:
ok so based on your pointers I went to the back of the ST60 wind instrument and pulled out the socket which feeds the MHU at the top of the mast. As you say, it should feed 8v to the MHU and therefore any readings directly out of the back of the ST60 Wind instrument should only read 8v at Red to Screen since all the others are receiving a signal back.

The voltages from the back of the instrument are as I mentioned above. Ita getting 7.8v on Red / Blue and Red / Green.

So this would say the unit is faulty and feeding bad signal up wires that should be receiving signals back from the MHU. So I tried a spare ST60 unit and that did the same. I then tried a third and also the same. Surely all three of my spares aren’t faulty.

Are sure about voltages I’ve taken with no MHU attached?
Click to expand...
I think that taking voltages across the coloured cables is always going to be misleading. All the voltages are referenced to ground which is why I keep specifying yellow/green/blue to screen. If you test the terminals at the back of the ST60 display and yellow to screen produces 5V with no MHU connected then I'm sure that there must be something wrong. Yellow/green/blue to screen with no MHU connected must be zero.

Do all your ST60s. when disconnected from the network, show 5V yellow to screen?

Richard
 
RichardS said:
I think that taking voltages across the coloured cables is always going to be misleading. All the voltages are referenced to ground which is why I keep specifying yellow/green/blue to screen. If you test the terminals at the back of the ST60 display and yellow to screen produces 5V with no MHU connected then I'm sure that there must be something wrong. Yellow/green/blue to screen with no MHU connected must be zero.

Do all your ST60s. when disconnected from the network, show 5V yellow to screen?

Richard
Click to expand...
Thanks ok yes that makes sense. I’ve left the boat for a few days so I’ll test again when I get back for Screen to Yellow.
 
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