This afternoon i managed to :
-1- desolder the GBU12G ( was very complicated because of 4 legs to heat together and some kind of rivets clamps fitted on the 4 concerned holes of the board ... long story )
-2- test the L7824 fitted with a tiny heatsink : the resistance was a lot different along one leg from top to bottom : i decided to replace this component with the same one from my second board.
-3- put everything back together.
Tomorrow : put the board and the motor back onto the mill and test with new fuses....we will see !
Some pics :
Last edited by BILLYBOUM; 01-01-2014 at 11:55 PM.
The L7824 is a 24volt voltage regulator. Resistance measurements across it's legs tells you nothing about it's condition.
They're pretty indestructible, having built-in thermal shutdown, output current limiting and short circuit protection. About the only way to kill one is to exceed the max input voltage, apply a reverse input voltage (e.g. if the rectifier has failed short-circuit) or connect the output to a high voltage. If it's been replaced or needs replacing then there is likely to have been something catastrophic happen to the board and many other parts may also need replacing.
Last edited by irving2008; 02-01-2014 at 12:05 AM.
Thanks Irving : about L7824, i thought some people bent this component too much and broke the middle leg ( ground as far as i understand ) and repaired it with a tiny bit of metal included in solder ( that was looking really clumsy )
Anyway, i replaced it with the one from my second board because it looked just better ( can't hurt though )
As a conclusion, because the GBU12G was tested ok, i'm afraid nothing has changed and fuses will blow again.
W'll see !))
Many thanks anyway !!!
Any luck with this yet ?
No much luck but not desperate because i tried this sequence :
-1- powered up the board without connecting the motor : everything looks OK ( many leds light up, speed control screen light up )
-2- plugged in the motor : nothing special happened !!! ( power lines plus Hall control pack )
-3- started the motor w/o any load : BING ! everything goes dark in my workshop...
-4- unplugged the motor and try to power again : the board looks still alive !!!
Difference before and now :
-1- i changed my usual power line ( 220V fuse protected 20A ) to another line ( differential switch 10A protection )
-2- the 2 fuses on the board ( T10A ) don't fuse anymore - before, fuses were 6.3A ( no tempo ) ( but the differential switch now trips on my main power board )
Do you think hall sensors can "dislike" too much load requested on the motor - even for a short while ??? ( because that moment was the origin of the problem : i requested too much an effort on the milling so that it blocked suddenly the head rotation and stopped and blow the fuses )
Many Thanks Guys !!!
Last edited by BILLYBOUM; 02-01-2014 at 11:26 PM.
Sorry to have to say this, but your lack of understanding of electronics means you are clutching at straws. Almost certainly one or more of your output MOSFETs is faulty. Simple resistance measurements may not reveal which as it may only fail under stress. Your only option is to replace them all with known good NEW ones, you cannot assume the ones in the other board are good. Even then there may be some other failed component which will cause one or more of the new MOSFETs to fail, e.g. a dodgy high-side driver, leaving you back at square 1. You need more knowledge and more equipment than a multimeter to fault find this board.
Question: the GND wire on the hall sensor pack that you had to resolder. Was that disconnected after the fault or did it become disconnected when you disassembled the motor?
Last edited by irving2008; 03-01-2014 at 06:43 AM.
It's true what Irving is saying but in the interests of keeping things cheap and easy try this first.
I'm guessing you mean the RCD is tripping, in that case you may have put something to ground that should not be, it only takes a few mA to trip it. Check the motor to make sure nothing is down to earth on it.
I didn't realise that you have stalled the motor while cutting. As Irvine says you have probably taken out the output stage. Try replacing all of them as he says and see what happens. But you could also have cooked the motor as well which a simple test meter wont show. You need and insulation tester to check it out correctly.
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The idea was to keep things cheap and practical considering the price of that board is around 1.000 euro - so even if i could replace all components, it should be cheaper than buying a new one at manufacturer.
From the start, I came to a specialist in electronics and TV boards : he said he was not able to repair my board ( despite all his oscilloscopes and stuff in his workshop ... ) so apparently, this kind of problem is not so easy to solve even for professionals.
I understand and thank you for your technical comment :
Your only option is to replace them all with known good NEW ones, you cannot assume the ones in the other board are good. Even then there may be some other failed component which will cause one or more of the new MOSFETs to fail, e.g. a dodgy high-side driver, leaving you back at square 1. You need more knowledge and more equipment than a multimeter to fault find this board.
Last edited by BILLYBOUM; 03-01-2014 at 12:26 PM.
A hi-fi/TV repair place wouldn't know where to start. This is a specialist job - you need to know how brushless controllers work to start with. I suspect the manufacturer wouldn't bother fault finding, its too labour intensive, they'd just replace the board. If it was mine, I'd have a go, but then I've designed these controllers before so I have some idea what I'm looking at.
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