The Shop > Electronics & IC Programing

KBIC controller probs

(1/6) > >>

Gazz292:
Hello all,

not posted on here for a while, havent used me lathe over summer, but now the nights are drawing in, i'm starting up my indoor projects, and the problem with the lathes controller board is playing up again,

the lathe is a version of the real bull 7x12 mini lathe, http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=110653275767&ssPageName=ADME:X:AAQ:GB:1123

It's got a KBIC 240D, 477ic controller board in it, and an unmarked second board with a transformer, relay, few big resistors etc,

Problem i have is the lathe can work fine, i can take light or heavy cuts, motor keeps it's speed nicely, then i can turn it off, and it wont turn back on,
very occasionaly it'll cut out whilst i'm using it, can be the second the tool touches the material (only alli or delrin been used so far by me) or half way through a cut,

sometimes it will power back up after a few minutes of being left off, sometimes it'll be a few days, no ammount of wire waggeling, tapping, unplugging and re-plugging it in will influence when it decides to work again.

i have tried adjusting the trim pots on the board, no difference except those expected, i.e. min and max speed, acc. etc,

i have re-soldered all even slightly suspect joints, tested continuity, something is causing the second board to keep the power off.....


i know this as i found out that when it's cut out, turning the speed knob on, the relay on the second board clicks in, that's when it wont power up, but i found that it's still braking the chuck, i.e. if i turn it backwards it will fight me,
and i found out that if i turn the low speed pot up, the motor will run, i can get about 700 rpm by upping the min and max pots, this is with the main speed knob set to OFF, i have directional controll via the switch too,

so i guess that shows the scr's and diodes are working as it runs the motor, just something is tripping it out, and i'm not sure what.

one thing i have noticed is the green resistor on the main board gets hot, even when the motor is not running, when running it gets hotter still, so i guess that could be pointing to something to do with the fault, but letting that resistor cool right down dosent cure the problem, and even when it is very hot, it's still measuring resistance, so it's not going open circuit, or short circuit.

the photo's show the main board, the resistor in question and the second board with the relay that is cutting power to the motor,

anyone got any ideas what the problem is? or do i just bite the bullet and get another controller board... problem being i have not seen any mention of the secondary board on any sites that looks like mine, i.e. the transformer is on it, and the tacho works from it too,

John Swift:


Hi

in the third picture the pcb with the transformer
it looks like the transformer is for the 5V power supply for the tacho

plus an interlock that I've seen on another lathe using the KBIC 240D speed control board

John

andyf:
Just a thought, Gazz: have you checked the motor brushes? I understand they can sometimes give rise to intermittent faults.

It seems you are reasonably certain that the KB control board is working, but for future reference the manual (which covers all the KBIC series) is at http://www.kbelectronics.com/manuals/kbic_manual.pdf . It no longer includes the schematics, but send me a PM if you ever need those.

Andy

Gazz292:
checked the brushes, they are fine, hardly worn at all, and move in the holders easily,

the motor runs the same as normal when i twiddle the min speed trim pot when the controller has shut down, i.e. sounds the same, has torque etc, infact i used it like that to finish a job off when i last used the lathe months ago,

i imagine that big resistor thats getting hot is part of the problem, but i dont know enough to figure out what it's function is, it could be for overload purpouses or something, and is actually doing it's job?

makes sense the transformer is for the tacho power,

i am tempted to remove the power feed to that relay, and see what happens when it can't lock the motor out, i imagine i'll loose the braking function, and prolly blow the main board as well,

David Jupp:
No direct experience of this board - just guessing based on symptoms.

If motor won't turn, but is braking - could this be a 'quick stop' function.  If so I would suspect a poor connection or faulty contact in the circuit containing any stop buttons or interlocks (guard closed switches).

Shorting out any suspect switch or wire temporarily (whilst taking safety precautions - safety interlocks are there for good reasons!) would reveal if this is a likely cause.  I'm assuming here that the interlock circuit is closed in the 'safe' and open in 'unsafe' conditions.

Navigation

[0] Message Index

[#] Next page