Author Topic: KBIC controller probs  (Read 25529 times)

Offline Gazz292

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KBIC controller probs
« on: September 30, 2011, 08:49:12 AM »
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,

Offline John Swift

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Re: KBIC controller probs
« Reply #1 on: September 30, 2011, 02:01:19 PM »


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


Offline andyf

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Re: KBIC controller probs
« Reply #2 on: September 30, 2011, 03:12:14 PM »
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
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Gazz292

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Re: KBIC controller probs
« Reply #3 on: September 30, 2011, 07:52:45 PM »
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,

Offline David Jupp

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Re: KBIC controller probs
« Reply #4 on: October 01, 2011, 04:09:41 AM »
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.

Offline picclock

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Re: KBIC controller probs
« Reply #5 on: October 01, 2011, 05:05:05 AM »
Just a thought, it may be the speed control pot itself. Wiggling it or tapping it when the fault occurs may indicate this. Easiest way to test if intermittent is to replace.

Best Regards

picclock
Engaged in the art of turning large pieces of useful material into ever smaller pieces of (s)crap. (Ferndown, Dorset)

Offline Gazz292

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Re: KBIC controller probs
« Reply #6 on: October 01, 2011, 08:48:49 AM »
speed pot, something i havent tested, the switch part of it works fine, as the relay clicks on when the knob is turned to on, and off when it's turned to off,
tapping the pot knob does nothing, but if the track is bad at the very begining, the board may be locking out as it thinks it's trying to be started up at a position other than low speed,

the guard interlock works the NVR switch, basicaly power is routed from the nvr thru the guard interlock then to the board's input.

Offline Gazz292

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Re: KBIC controller probs
« Reply #7 on: October 01, 2011, 10:03:39 AM »
not the speed pot, that measures out fine,

i did notice one of the transistors on the second board gives a strange reading, between middle and one leg short, both ways, no circuit between middle and other leg... both ways, that's not good me thinks, and that particular trannie is the one that one of the wires from the main board goes through to get to the rest of the circuit,

looking up the numbers now to see where i can get one, i bet maplins wont have em, heck, do they even sell electronic components anymore, just thing how many more kiddies toys they can fin in the shops if they get rid of the electronics stuff.

i did try something... the second board has wire marked I2, which i assume is inhibit, it goes to I2 on the main board, with that wire disconnected it's still the same, so i'm guessing the second board is inhibiting the main board,

oh yeah, just in case anyone knows their transistors.... the one in question is 'MCR 100-6 P86'  there is one other transistor on that board, and that is 'CJ 78L05 011'
if i can find replacments for those 2, i'll bung them in and see what happens,

Offline John Swift

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Re: KBIC controller probs
« Reply #8 on: October 01, 2011, 10:13:08 AM »
78L05 is a 100mA 5v regulator in a TO92 case    http://www.alldatasheet.com/datasheet-pdf/pdf/6798/NEC/78L05.html

   John

ps        mcr 100-6 is a thyristor   http://www.alldatasheet.com/datasheet-pdf/pdf/4632/MOTOROLA/MCR100-6.html

Offline andyf

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Re: KBIC controller probs
« Reply #9 on: October 01, 2011, 10:36:30 AM »
Does the Current Limit LED fitted on the KB board (near the "A-" connector) light up when the problem arises? If so, it might be worth noting the setting of the CL trimpot and then giving at a twiddle or two before returning it to the original setting.

I suppose one way of establishing if the KB board is the problem would be to bypass everything but that board and the motor. This could be done with a mains plug (with a 3A fuse in it for safety) in a switched wall socket, and a flex taking the live and neutral direct to L1 and L2 on the KB board, with the earth going to wherever the existing earth terminal is on the lathe. Leave the speed pot connected to P1, P2 and P3. Then, connect A+ and A- on the board direct to the motor. If there are connections to I1 and I2, disconnect them.

In effect, your KB240 is now connected up just like the one I have fitted to my old milling machine, except that I put an NVR switch on that.

With the speed pot turned down to slow (but not clicked off), turn on the power at the wall switch and then wind up the speed pot to see if the motor runs normally. If the spindle turns in reverse (there is now no Fwd/Rev switch in circuit) then it will probably only run at half speed, just as it did when all was well. Transposing the connections to A+ and A- will get it running forward and at full speed.

If the problem disappears, then the KB board is OK.

Remember that mains voltages are involved, so be careful. If you feel at all nervous don't try this test.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Gazz292

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Re: KBIC controller probs
« Reply #10 on: October 01, 2011, 11:21:21 AM »
this board dosent seem to have the overload led as mentioned, i've looked all ove the board for any surface mount leds, none to be seen, and deffo no thru hole mount ones, there's an empty solder pad set for a power on led too,

i think it is time to try the board on it's own, at least i'll know which board is giving me trouble,

Offline Gazz292

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Re: KBIC controller probs
« Reply #11 on: October 01, 2011, 11:53:33 AM »
 :zap:
not really, it's the bottom board at fault,

she runs fine directo off the main board,


so what to do, the bottom board provides the tacho readout, but that part is still working, so i can re-wire it so it still gets power to run the tacho bit,
seems that board provides the brake, which only works when the emergancy stop button is pressed (i.e. remove main power, it dosent brake when i turn the speed control to off)

it also seems to provide some interlocking, i guess the thing to allow the motor to run only if the speed control is off,

i'm not sure if the main board can do that too, via the switch in the speed pot and the inhibit input,

i'll see if i can get those 2 transistors and see if that fixes the bottom board, but untill then, and if it dosent, i'll re-wire it to run only on the main board, with the direction switch in the circuit too,

i expect the bottom board also kept power off if the direction switch was changed whilst running, i always stop before changing direction on any power tool anyway, too much stress put on them, so it's only really the brake function i'd loose,

Offline andyf

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Re: KBIC controller probs
« Reply #12 on: October 01, 2011, 12:20:37 PM »
.....i expect the bottom board also kept power off if the direction switch was changed whilst running, i always stop before changing direction on any power tool anyway, too much stress put on them, so it's only really the brake function i'd loose,


I think you're right there, Gazz - do a proper stop (big red button) before changing direction. Otherwise, according to the second warning on p13 of the manual http://www.kbelectronics.com/manuals/kbic_manual.pdf  it looks like damage might result when that switch disconnects completely in passing between the forward and reverse positions.

It's good that you have narrowed down the problem. If you can't fix the bottom board, you can probably get a new one from Amadeal. Unless you have already done so, it would be worth checking any safety interlock switches like the one on the chuck guard (if fitted). If one of those is open circuit when it shouldn't be, the lathe won't start.

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Gazz292

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Re: KBIC controller probs
« Reply #13 on: October 01, 2011, 03:10:31 PM »
Deffo not the chuck guart interlock, that passes incoming mains thru it, so when it is opened it removes power, and thus trips out the no volt release switch, requiring the green button to be pressed to get power back after putting the guard back down,

the I2 terminal was fed from the secondary board, which i guess shut the main controller down when the direction change switch was operated, whilst it was braking etc,

the direction switch is a multi pole rotary one, havent traced their connections yet, but it has a feed into it from the speed pot's switch, which gets it's feed from the secondary board from a terminal marked 'TG'  and the switch in the pot is open when the knob is in the off position,

theres also wires to the reverse switch from the secondary board marked 'TA' 'V/2' and 'I/O'
there's also a feed into the direction switch from one of the speed pot's outer terminals, that's ran in paralell to the P3 terminal on the main board,

and L1 on the main board is fed from the secondary board, L2 is paralell with the secondary board, fuse,light and NVR switch.

Offline Gazz292

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Re: KBIC controller probs
« Reply #14 on: October 01, 2011, 03:36:47 PM »
78L05 is a 100mA 5v regulator in a TO92 case    http://www.alldatasheet.com/datasheet-pdf/pdf/6798/NEC/78L05.html

   John

ps        mcr 100-6 is a thyristor   http://www.alldatasheet.com/datasheet-pdf/pdf/4632/MOTOROLA/MCR100-6.html

so the 78l05 is prolly to power the led tacho display, if so it's working fine,

the mcr 100-6,
i guess it's suposed to block current flow one direction all the time, and when the gate is fed power, it opend and lets current flow the opposite direction?

seen the diagram from that data sheet, and i should get a short reading between the cathode and gate pins in both directions, but i should get a resistance flow thru anode to cathode, but not cathode to anode unless the gate has been triggered?
attatched the drawing of the pin layout from the data sheet,

i'll take it out of the circuit and test it, but it could be something else on this board thats gone.

Offline John Rudd

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Re: KBIC controller probs
« Reply #15 on: October 01, 2011, 03:49:05 PM »
i should get a short reading between the cathode and gate pins in both directions, but i should get a resistance flow thru anode to cathode, but not cathode to anode unless the gate has been triggered?
attatched the drawing of the pin layout from the data sheet,

The scr should behave as a diode when the gate is triggered.........A to K forward biassed
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Offline Gazz292

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Re: KBIC controller probs
« Reply #16 on: October 01, 2011, 04:09:44 PM »
gotya,
this second board seems pretty simple, just 2 transistors, one of them the scr... which is even marked as a diode on the board (D4) the other one a 5 volt reg,
theress 7 capacitors, 2 other diodes, 3 small resistors, the big brake resistor, 1 relay, an inductor, transformer and a bridge rectifier,

i'll take it out of circuit, and try to figure out what bit does what.

Offline Gazz292

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Re: KBIC controller probs
« Reply #17 on: October 01, 2011, 06:06:07 PM »
i have me lathe working again,

bypassed the brake board, but kept power to it so the tacho still works, ment changing one wire, L1 was fed from the second board thru the relay, so it now has live to it from the nvr,

disconnected a load of wires, they all when through the direction change switch appart from 1, which went to I2 on the main board,

figured out it's that board that does the reverse speed slow down bit too, one of the stack of switches in the direction change switch operated only in reverse setting, and connected 2 pins together on the second board, which reduced the reverse speed available.

it also handled the 'return speed knob to zero before it'll turn on function'
but the main board ramps the power up slowly, and i read it can handle that, i'm used to turning the speed knob to off to stop the lathe anyway,

and i've put the reverser switch in forwards and taken the knob off, so i wont be tempted to change motor direction with the board powered up,

asked amadeal if they can supply the secondary boards, the controller board they list on the site is for the 7x12 lathes, mines the 7x14 (i always forget), which has a different power board and location of controls it seens,

Offline Swarfing

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Re: KBIC controller probs
« Reply #18 on: October 01, 2011, 06:12:02 PM »
Sounds like the breaking resistor is at fault. If it is not doing it's job then it will trip? try swapping it out for a decent sand block of the same value.
Once in hole stop digging.

Offline John Swift

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Re: KBIC controller probs
« Reply #19 on: October 02, 2011, 09:28:32 AM »

Hi Gazz


if the interlock circuit is as I expect ,
a momentry loss of mains supply could cause the relay to drop out

I found not all the lucar push on connectors used on my lathe to made a good connection
(i'm sure one was only held in place by the rubber boot)

 the switch on the back of the potentiometer triggers the thyristor when the speed control is fully anti clock wise
the relay then switches power to the speed control board and the DC output (via the FWD/REV switch) to the motor
only when switched off the motor is connected to the breaking resistor

my guess at the circuit is below

John


Offline Gazz292

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Re: KBIC controller probs
« Reply #20 on: October 04, 2011, 06:26:42 PM »
well, i sent amadeal an e-mail describing the board, what functions it does, what lathe i have etc,
the reply said that for £25 plus a tenner postage he'll sell me a 'filter board for a CJ18 lathe'

erm, a filter board is usually just a few capacitors and a choke or 2, i guess is hould ask him if he thinks that brake/interlock and tacho board is a filter board, but to be honnest, i'd rather spend that £35 (if i had it) on a bar of 120mm delrin.

The lathe runs fine without it, i just have to not be silly and try to change direction with the machine running, and look where the speed knob is before turning it on (but so far when i turn the speed up to polish something, after i'm done i turn the speed back down) and i'm unlikely to put anything in the chuck that can't withstand 1100 rpms for a second or 2.

i've been thinking of taking the relay and brake resistor off the board and wiring them up as shown on the instructions for the main board,

i have noticed that resistor i pointed out on the main board that was getting extremely hot, isnt doing it now, it gets warm but only when the lathe is in use,
with the interlock board in the circuit, that resistor would get very hot even if the motor wasnt running (main power on via the NVR switch, but lathe off via the speed pot switch)

the resistor has been hot enough to burn off the colour bands, so something deffo wasnt right.

Offline andyf

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Re: KBIC controller probs
« Reply #21 on: October 04, 2011, 07:19:49 PM »
If the resistor is the big green affair between the relay and the transformer on the "filter board", it probably didn't have any colour bands - power resistors usually have their value printed on.

For reasons too vague to explain, I think it might be worth pulling out the blue relay and checking that it's switching on and off properly (to make sure, for example, that its contacts aren't welded together). If I correctly understand what you have done, it isn't doing anything now, so removing it shouldn't cause any further problems . 

Maybe fit a flap over the Fwd/Rev switch to remind you to turn off before changing direction?

Andy
Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Gazz292

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Re: KBIC controller probs
« Reply #22 on: October 04, 2011, 08:52:13 PM »
the resistor that baked is on the main speed control board, shown in pic 2 of my first post, photos of other controllers show it was deffo a banded resistor,

the brake resistor is a big green wire wound jobbie, with the resistance printed on it,

basically i'm only feeding power to the secondary board to run the tacho, so yup removing the relay and big resistor wont stop that working... i hope,

i keep the knob removed from the direction change switch, so i have to think before i change direction, but it's not something i think i would do anyway, might catch it one day i guess, and in doing so turn it to off, which will blow the speed board it seems,

the direction switch has a 'spare' switch stack now, it handled the interlock function before, i guess i could use them for my own interlock, maybe using a relay to cut main power, so the no volt release switch drops out if i move the knob whilst powered up,

Offline andyf

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Re: KBIC controller probs
« Reply #23 on: October 05, 2011, 04:09:48 AM »
Oh, THAT resistor (said he, not having a clue what it does). According to the components list for the KBIC series, on a 230V model it should be 15K-5W/70°C-5%.

Ive sent the parts list and schematic to your email addy, in case you want to try and work out what has been turning the resistor into a slow-blow fuse.

Andy

Sale, Cheshire
I've cut the end off it twice, but it's still too short

Offline Gazz292

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Re: KBIC controller probs
« Reply #24 on: October 05, 2011, 06:08:45 AM »
thankyou to everyone who has helped me with this problem, and thanks to andy for the schematic,

i've had a little look, but can't figure out what was causing the resistor 17a to overheat, but it was deffo caused by that secondary board, so it can stay out of circuit,

So if i blow the main board by changing direction whilst the chuck is spinning, or i start her up at full speed with some fragile material in the chuck and explodes due to the G-forces, then it's my fault, and i'll either learn from the experiance, or it'll be the last thing i do  :zap:

i'm old enough and daft enough to take responsibility for my own actions, and i firmly believe that i am the one to blame when i do something wrong, not the maker of the machine like some people in the world,
(read a story recently of someone who bought a table saw, was offered the version with a safety devise that stopped the blade and dropped it in the machine if it detected you cut into your hand, he declined as it cost more than the machine without it, he promptly chopped a finger off, then sued the shop for letting him buy the machine without the safety brake  :drool:

Anyway... to be honnest i found the need to set the speed knob to zero every time i wanted to start it up a bit of a pain, i much prefer it now, i set the speed to what i think is good for the material, and leave it there, i get the same speed next time i start up after taking a break to get my legs working again,

and i wont leave the lathes main power on overnight again because i stop it via the speed knob and forget the main switch, well actually the darn thing had cut out on me for about the fifth time that day, and i'd walked off fed up that every time i got the hang of the way i was doing something, it'd die and i'd have to start over again (i've only just made my very first object on the lathe, so im learning a lot fast, but it's so much easier to learn new things if you can't complete what you start)

R17a was already toasty before i left it powered up overnight, but scary to think it could have gone up in smoke,
 
i keep saying i will put in a dedicated power circuit for the bench mounted power tools, a new radial circuit from the consumer unit in the garage thru a no volt release switch, then to the sockets, and some mushroom emergancy stop buttons at knee height along the bench infront of each machine,
hitting one of them will interupt the power feed to the NVR, causing it to drop out, so a reset is needed at the main switch, which will be by the door, so i can turn the circuit off as i leave.

i could even make a cover up that goes over the light switch, opening the cover operates a switch that knocks the nvr off,or i could put a switch in the door lock... or i could just look for a better functioning brain on ebay  :bang: