Hi u all,
This electronic card drives a well pump, with lack of water detection. Since several months, there is a problem that I can't solve :
for an unknown reason, the L10 led ( lack of water) lights on, and the pump stops ! If I turn off the main power ( before the transfo ) for 2 or 3 mn, and turn it on again, it works again, and it works sometimes several days, but sometimes only a few hours.
I've already changed all the caps (it didn't help), then the relay RL10 (it worked then flawlessly for 2 months !!! )
All that I have is the schematic and the wiring diagram I've attached. I'm not sure I quite understand the way all this works 
I also attach an image of the card (picture taken before I made any change ) .
If any of you can help me to solve this, I'll pay him a glass of......... water 
thanks,
jf
PS: as you can see, it is an old card (more than 15years old) - I think I'll replace it all with an arduino, but before, I need to know exactly how the electrodes ( low and hi level) work ...
BTW, there is no thermal relay , the '95' connexion goes to A2 of the contactor .
arf.... nobody has an idea of which component might be faulty ?
maybe the transfo : when it works, I hear no noise, but when it doesn't work, there is a "bzzzzz" (50Hz, I guess) which seems to come from the transfo.
It is hard to imagine that it would be worth your time to figure out how the low-water shutoff circuit works and then attempt to duplicate its function with an Arduino. Projects that combine power electronics and an Arduino are not for the inexperienced. I suggest to just buy a suitable replacement -- a local water well/pump company can advise you on the choice.
thanks for the answer.
replacing the low-water shutoff circuit shouldn't be that difficult. As far as I can see, if there is current through RE and EB, than there is water in the well, if not, the pump must be stopped. All I need to know is the minimum value, under which I must shut off the pump.
The pump is turned on when the pressure switch is ON ( if no lack of water, indeed).
But I'll do that in several weeks, when I have time.
For now, I'm trying to figure out what causes this weird behaviour, which component is the culprit, and change it.
What makes it difficult is that it is a "random" breakdown, not reproducible .
Buying a whole replacement system would be too expensive for the house owner ( I'm only an occupant ) .
And now, I'm frustrated, I need to understand
PS : Actually, I'm not "inexperienced", I studied and worked in electronics ... okay..... long time ago , and I've been working on PLC for several years. But sure, I need to practice and remember .....
edit : typo correction
thanks, I'll have a close look at it
The random failures might not be caused by a component. A poor solder connection or frayed wire could also do that, especially if oxidized after 15 years of exposure. You might go around the circuit board with a soldering pencil and touch up all the joints.
you're right, I'll do that today
