Eltrim ST Trim Tab Control Repair

Hurricane said:
Watch out, John - things have changed over the years
Not the case for this little project but in my experience circuit designers now tend to use pic chips and simply wire inputs/outputs. Then internal software sorts out the logic. This makes tracing a curcuit a little more difficult and virtually impossible to copy. Often easier to start again.
So be aware when debugging more modern electronics.
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I know Mike, I wish I had more time to play, what with Rasberry-Pi and Arduino, all look like a lot of fun. The problem(s) found on the PCB look like the results of one corroded (sea-water ingress) tactile switch which has also corroded the adjacent tracks, all easily cleaned-up and by-passed so far! One passive component (resistor) looks bad, not burnt-out, but corrosion prevents me reading its colour coding. I could break one end and measure it but then I dont know if it has changed (unlikley, dont really want to break down the other unit!).

New switches are on there way from RS and hopefully Mark will send me his unit! Let's face it, with feedback pots on the motors I could measure voltage or even resistance to find out where the motors are! It would be easy using the pot as a voltage divider to knock-up your own circuit, but you have to stick to original controls of course!
 
John100156 said:
I know Mike, I wish I had more time to play, what with Rasberry-Pi and Arduino, all look like a lot of fun. The problem(s) found on the PCB look like the results of one corroded (sea-water ingress) tactile switch which has also corroded the adjacent tracks, all easily cleaned-up and by-passed so far! One passive component (resistor) looks bad, not burnt-out, but corrosion prevents me reading its colour coding. I could break one end and measure it but then I dont know if it has changed (unlikley, dont really want to break down the other unit!).

New switches are on there way from RS and hopefully Mark will send me his unit! Let's face it, with feedback pots on the motors I could measure voltage or even resistance to find out where the motors are! It would be easy using the pot as a voltage divider to knock-up your own circuit, but you have to stick to original controls of course!
Click to expand...

John, It will be easy for a man that already owns a desoldering tool! The hardest bit is getting the box open to get to the switches and you have already done that.

Here is a circuit diagram from (three years old) memory! Don't take it as read check it yourself then publish it here for others to use:
 
Aaarh, that's useful, I think I now understand how it works, if I take the resistor values that set voltage on the first leg of each of the gates, then as the pot alters the voltage on the common second leg of the gates, the LED's are switched on or off. Thanks for that, I've been working today at SELEX Galileo but will have a play tomorrow!
 
Well, on Sunday I traced-out the Eltrim Flybridge tab controller (110mm x 110mm) printed circuit board and identified the function of the four internal chips which are simply LM339N Quad Differential Voltage Comparators. I will draw-up the relevant parts and post later this week.

You can test the unit by applying 12v –ve to terminal 9, 12v +ve to terminal 2, then by inserting one leg of a pot (variable resistor) connected to 12v +ve (terminal 2) with its slider connected to terminal 6 (stb led’s) or terminal*5 (port led’s) then, as you adjust the pot, it will ramp-up/down the led's. I only had a 4.7k ohm pot (only one I had in my box) so adjusting would only set the correct voltage at the comparators to operate 5 led's in sequence but if you put 12v -ve or alternatively 12v +ve on terminals 5 or 6, it will switch all led’s on/off! Simple circuit, as I say I will crudely draw it up later.

The four tactile switches simply switch a -VE to output terminals the numbers will be seen on the drawing once complete - hope this helps others.
 
Thanks to PRM's starter for 10 - I managed to draw-up most of the circuit for the Eltrim fly bridge tab controller schematic as follows....

There may be a few other passive components on the board that I may have missed, together with showing the power to each of the four chips, which connect to pins 3(+) and 12(-) to each LM339N.

Resistor values are as accurate as I can get them, my resistor colour code is rusty to say the least, but it looks like there is around 0.16ma current flowing through each comparator with a resistance of 9,190 ohms, so this should give around a 1.5v drop between each stage activating its led.

Led staging set by each voltage comparator seems to go something like: 0.75v, 2.25v, 3.75v, 5.25v, 6.75v, 8.25v, 9.75v, 11.25v with the final 0.75v volt drop across the 4.7k end of line resistor (0.00016A x 4700 ohms = 0.75v) to make up the 12v range.

Hope this helps anyone like me, trying to cheaply test and/or repair their own units:

Eltrim_zps304cc29e.jpg
 
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