The Shop > Electronics & IC Programing
HELP!!!
John Swift:
Hi Grinder ,
If you need to test the speed control pcb , try this test circuit
I have used it when working on my controller
ps the motor brushes are not too short are they ? new ones are about 0.55" (14mm) long
John
pps not sure of circuit downloaded for FC350BJ (fc350 3 in earlier previous post)
on my FC250J/240v pcb terminal P4 is connected to a 10K resistor , not to P1
linking P1 and P4 or not , changes the level of the motor voltage feed back
on my lathe the maximum speed in reverse is half that in forward
see "part fc250 main pcb"
John Swift:
Hi Grinder ,
even more info
the circuit of my FC250J/240v control looks like a cutdown version of
your control without the overload protection circuit
John
grinder:
Hi John,
I took out the PCB today, and it looks like the damage is more than I first thought. There is a row of pots along one side of the board, and between VR1 and VR2, I noticed a sooty deposit around the SMT resistors, and one small electrolytic cap has a blown pressure relief on top. I'm thinking now that I should try to replace this board, and tackle the repair when I have more time. You have some great information though, thanks again
John Swift:
Hi Grinder ,
if you have not had much practice with SMT boards , get an old computer board to practice on first
my board and others I've helped on the model-engineer.co.uk forum , have had faulty capacitors
(thread :- speed control pcb for clarke cl300 lathe)
some measure ok for capacitance but the ESR is high ( several ohms instead of half an ohm at most)
with luck the deposit is from the capacitor ( is it C9 a 1uF 250v electrolytic by any chance ? )
if its one of the one's I suspect , it's been heated by R1B in the photo (0.34 ohms 5w)
hot capacitors have a short life - i've changed a few in switch mode power supplies inside of TV set top boxes and LCD monitors
the electrolytic capacitors are easy to replace
the SMT components under the protective laquer are more difficult
good luck
John
grinder:
Hey John,
I just saw your pic, and the cap that blew is the one to the right edge of the red box (C12). The board you show there is practically identical to my board, and the sooty deposit was over the SMT resistors in the box. If I can't find a replacement, I may just go in and change all the IC's and hope for the best. I do work with a lot of electronics stuff and feel capable of repairing this board, but most of the work I do is thru hole.
Thanks again for all the info
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