Author Topic: poorly seig c3  (Read 2543 times)

Offline davidcurtis021

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poorly seig c3
« on: June 06, 2017, 11:19:17 AM »
hi all

hav'nt been around for a while but could really use some help. On Sunday my machine suddenly died in it's sleep. it didn't give any warning symtoms just failed to restart after tea. it appears to be electricly comatose but i can confirm with basic testing that there is power in up to the emergency stop switch the internal fuse is ok and the motor does run when connected to my 18v drill battery.

i also put a multimeter over the transformer and while i got a reading between the two outer terminals on the secondary coil. i get an out of range reading for the centre one. does this mean the transformer is kaput.

is there also anything else simple i should be checking.




Offline John Rudd

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Re: poorly seig c3
« Reply #1 on: June 06, 2017, 12:11:05 PM »
From what I can see on the print side of the board, the centre pin isnt connected to anything....
That said, it could be that the transformer is centre tapped...
Need to see what is on the component side of the board....
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #2 on: June 06, 2017, 01:32:24 PM »
hi
thanks for the help there is definately a connection in the centre i, tried to get a photo but my camera wont stay steady enough,



 i also tried to get some other views of the top.







Offline John Rudd

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Re: poorly seig c3
« Reply #3 on: June 06, 2017, 02:16:11 PM »
What is the chip at the end of the board next to the 2 pin socket?
I'm guess its a 7805 regulator..

With power applied, is there any voltage at the two pin socket?
I looked at the photo above in your album, looks like the secondary of the transformer isnt centre tapped....the two outer connections go to a 4 diode bridge, then the regulator....
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #4 on: June 06, 2017, 03:12:39 PM »
hi
yes that is the number printed on it when i put the multimeter on the underside of the 2 pin socket i got a reading of 56.7mv in dc i assume that is 5.6volts

Offline John Rudd

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Re: poorly seig c3
« Reply #5 on: June 06, 2017, 03:32:17 PM »
Well is it 56 mV or 5.6 Volts? Hmmm....Depends on what range you have set on your meter.....

Ok, looking at the front of the regulator ( where the numbers are...) the connections are; 1,2 &3 left to right.....connect your meter Black lead to the tab, now connect the Red lead to pin1.... What reading do you get? Set the meter to the 20 range DC volts....then transfer the Red lead to pin3, what reading is on the meter?
Apologies if this is all simplistic, but I dont know what electronic knowledge you have....( I'm a retired engineer,with an electrical/electronic background)
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Offline super7

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Re: poorly seig c3
« Reply #6 on: June 06, 2017, 04:11:55 PM »
Is it not strange that you are getting 0 ohms across the secondary coil in the first pic? Is that not indicative of a dead short ?

Offline davidcurtis021

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Re: poorly seig c3
« Reply #7 on: June 06, 2017, 04:13:31 PM »
Hi John

i will go and do as you suggest first thing tommorow the wife wont let me go out and play anymore tonight. please no apologies simplistic is good, in my former life i was a mushroom farmer so my toolkit was more stilson wrench and large hammer. my limited electrical knowledge came from our local electrician who taught me just enough to change a 3 phase motor or to check i was getting power.
i still take a deep breath and count to ten before going anywhere near live power.

incidently the meter range  was set to auto

Offline awemawson

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Re: poorly seig c3
« Reply #8 on: June 06, 2017, 04:15:23 PM »
A transformer winding will usually show very low resistance to DC. Remember that it is an inductor, and that it's impedance at supply frequency limits it's current, not it's resistance at DC. Same with motor windings.

Andrew Mawson
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #9 on: June 06, 2017, 04:22:35 PM »
Is it not strange that you are getting 0 ohms across the secondary coil in the first pic? Is that not indicative of a dead short ?

the reading wasnt exactly zero it fluctuated between zero and 0.003 my understanding is that is normal and a reading that is 0L indicates something amiss

Offline davidcurtis021

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Re: poorly seig c3
« Reply #10 on: June 06, 2017, 04:41:24 PM »
Well is it 56 mV or 5.6 Volts? Hmmm....Depends on what range you have set on your meter.....

Ok, looking at the front of the regulator ( where the numbers are...) the connections are; 1,2 &3 left to right.....connect your meter Black lead to the tab, now connect the Red lead to pin1.... What reading do you get? Set the meter to the 20 range DC volts....then transfer the Red lead to pin3, what reading is on the meter?
Apologies if this is all simplistic, but I dont know what electronic knowledge you have....( I'm a retired engineer,with an electrical/electronic background)

John when you say connect the black lead to the tab do you mean the silver part on top of the regulator. (just a double check before i do anything to make matters worse)

Offline John Rudd

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Re: poorly seig c3
« Reply #11 on: June 06, 2017, 04:45:57 PM »
Is it not strange that you are getting 0 ohms across the secondary coil in the first pic? Is that not indicative of a dead short ?
Super7, with the meter set to uts lowest range in Ohms, the transformer's dc resistance is so low, that it will practically read almost 0 ohms...( the secondary winding that is, because it has so few turns)
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Offline hermetic

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Re: poorly seig c3
« Reply #12 on: June 06, 2017, 04:51:15 PM »
You may be over thinking this! You say you have power to the stop switch, is there power coming out the other side of the stop switch? Did you use this stop switch to stop the machine? If so, check it is not stuck in the off position. Some of them lock off, and have to be reset to work again. Very unusual for something to fail with no power on, and also fail to even give a twitch when turned back on.
Hope this helps
Phil

Offline John Rudd

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Re: poorly seig c3
« Reply #13 on: June 06, 2017, 05:04:46 PM »
Have you got power to the speed control board? ( back to what hermetic was saying.... :thumbup:)
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #14 on: June 06, 2017, 05:22:23 PM »
thanks Hermetic  and john
yes i do have power out of the stop switch  my metholody so far has been to follow the power from the mains, into and out of the emergency stop switch down to the control board and into the transformer then at the transformer output is where i began to suspect i may have found a problem, but as said above i'm at level 0 when talking elecrtricals all i'm really capable of is following instructions and reporting back.

Offline John Rudd

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Re: poorly seig c3
« Reply #15 on: June 06, 2017, 05:27:17 PM »
Ok, so we know your level, we can guide you if you provide the info .... :zap:
Just dont go hurting yourself....240v isnt nice... :lol:
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #16 on: June 07, 2017, 05:09:14 AM »
Ok, so we know your level, we can guide you if you provide the info .... :zap:
Just dont go hurting yourself....240v isnt nice... :lol:

i thought it might help if i provided a diagram showing what i did yesterday as i don't have the proper terminology in my vocablary. possibly make it easier to understand and see where i have made blunders




that is not the number on my control board but the layout is the same in preview the picture looks too small to read apologies for that but i dont know how to make it larger.

john i have also taken the readings you suggested which from the left pin 008.9 centre pin 0 right pin 000.1 regarding the range button pressing it moved the decimal place to the right.

thank you for the patience which you have shown thus far

Offline John Rudd

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Re: poorly seig c3
« Reply #17 on: June 07, 2017, 05:22:06 AM »
So, do you have 5volts dc measured at the connector on the little power supply?

Can you post up a photo of your speed control board please?

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Offline davidcurtis021

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Re: poorly seig c3
« Reply #18 on: June 07, 2017, 07:22:43 AM »
So, do you have 5volts dc measured at the connector on the little power supply?

Can you post up a photo of your speed control board please?
i dont know about the voltage at the 5v connector when i went to measure i was getting inttermitent readings after which i discovered that the inline fuseholder had broken at the end so i had to suspend work till a new one arrives from arc eurotrade which will hopefully arrive tommorow

did take a picture of the control board though which is below.


Offline John Rudd

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Re: poorly seig c3
« Reply #19 on: June 07, 2017, 08:55:59 AM »
So, are you now thinking that the broken fuse holder is the reason why your machine isnt operational?
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #20 on: June 07, 2017, 11:06:03 AM »
So, are you now thinking that the broken fuse holder is the reason why your machine isnt operational?

i' can only wish but as i had a good reading at both ends yesterday morning when i started taking it apart i suspect i have managed to break it somehow and the broken fuseholder is just an aditional problem. however when i get a new fuseholder in place it might be prudent to start investigating from the beggining again.

Offline John Rudd

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Re: poorly seig c3
« Reply #21 on: June 07, 2017, 11:45:47 AM »
Here's a better wiring diagram....


  http://littlemachineshop.com/reference/drawings/4507-XMT-C3Lathe.pdf

It shows the chuck guard interlock, if yours has one...
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #22 on: June 07, 2017, 01:38:58 PM »
Here's a better wiring diagram....


  http://littlemachineshop.com/reference/drawings/4507-XMT-C3Lathe.pdf

It shows the chuck guard interlock, if yours has one...

thanks for that John. it proved very useful as it reminded me that one thing i had'nt checked so far was the microswitch on the chuck guard i dont know whether it is NO or NC but in any case a continuity test showed out of range for both ways so i know that is duff and am more hopeful that it was the root cause of my problem. when my fuseholder comes hopefully tommorow i will put a link across k3 and k4 and pray for success. Do you think that could have been the problem.


Offline John Rudd

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Re: poorly seig c3
« Reply #23 on: June 07, 2017, 02:13:30 PM »
Its very difficult to determine root cause of a problem without having 'hands on' during the investigation....
One can only speculate...
I'll wait until you resolve the fuse holder issue....
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #24 on: June 08, 2017, 08:37:04 AM »
Postman came and went without leaving me with a new fuseholder so took matters into my own hands and constructed a temporary holder from plastic tube



as anticipated other than give stable readings for the multimeter no improvement so next was to bridge the teminals that connected the chuckguard micro switch K3 and K4 on the drawing



On recconeting to the mains and releasing the emergency stop i now have power through the system and a small turn on the speed control brought the motor into life.



just like to say thank you to all who made suggestions and especially John for his guidance.

the upside is now i dont have to spend on  new electrics other than a microswitch i can lavish some cash on giving the machine a complete overhaul starting with the headstock and possible bearing change. followed by getting rid of the horrible digital readouts.


Offline awemawson

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Re: poorly seig c3
« Reply #25 on: June 08, 2017, 08:43:21 AM »
And does the beast now turn ?
Andrew Mawson
East Sussex

Offline davidcurtis021

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Re: poorly seig c3
« Reply #26 on: June 08, 2017, 08:53:37 AM »
And does the beast now turn ?

yes it does. Thank you for asking

Offline John Rudd

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Re: poorly seig c3
« Reply #27 on: June 08, 2017, 09:00:18 AM »
Just make sure you fit the new fuseholder.....and... Fwiw, despite what fuse is fitted, change it to a 3 amp fuse.....These machines tend to be shipped with fuses with a rating higher than necessary.
The result is either a blown control board or motor or both.....you could also check the fuse in the mains plug....again no more than 3 amps should be sufficient
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Offline davidcurtis021

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Re: poorly seig c3
« Reply #28 on: June 08, 2017, 09:09:45 AM »
Just make sure you fit the new fuseholder.....and... Fwiw, despite what fuse is fitted, change it to a 3 amp fuse.....These machines tend to be shipped with fuses with a rating higher than necessary.
The result is either a blown control board or motor or both.....you could also check the fuse in the mains plug....again no more than 3 amps should be sufficient

thanks John

i know for definate that the fuse in the plug is a 5 amp so i'll do that straight away.

Offline John Rudd

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Re: poorly seig c3
« Reply #29 on: June 08, 2017, 09:14:33 AM »
So, what is the justification for a smaller fuse?
Simply put, watts is volt x amps.
The motors on these small lathes are around 300-400 watts. So at max load they will consume no more than about 2 amps....Generally the speed controllers have in built protection to avoid over current, but should something  go awry, last level of protection is the fuse....

Thats my take on it and as it happens, is the same approach adopted by Warco, I'm told from sources on another forum
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Offline PekkaNF

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Re: poorly seig c3
« Reply #30 on: June 08, 2017, 11:21:23 AM »
Time-current characteristics
http://www.littelfuse.com/~/media/automotive/catalogs/littelfuse_fuseology.pdf

Looks like 3,15A fuse blows about 10A in 0,1 sec, would that card withstand 30A for 0,01s?
http://www.farnell.com/datasheets/1447843.pdf

Generally those fuses are fine when they are chosen to blow out on wire short circuit and prevent wires. To dimension these glass tube fuses to protect electronic circuit on small over current or surge load is not easy.

Another issue is selectivity. The mill fuse should blow before plug fuse and plug fuse should blow before mains fuse. Two fuses near same melting current is a bad idea.

Pekka


Offline John Rudd

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Re: poorly seig c3
« Reply #31 on: June 08, 2017, 12:34:50 PM »


Generally those fuses are fine when they are chosen to blow out on wire short circuit and prevent wires. To dimension these glass tube fuses to protect electronic circuit on small over current or surge load is not easy.

Another issue is selectivity. The mill fuse should blow before plug fuse and plug fuse should blow before mains fuse. Two fuses near same melting current is a bad idea.

Pekka

Pekka,
I was merely suggesting that to prolong the life of the machine, the the op change the fuses to a value lower than those originally fitted.
It is cheaper to replace a blown fuse in the event of a fault than have to buy a new motor or pcb.

The manufacturers of these machines will fit protective fuses, albeit with values that are far too high...the number of machines that have come my way for repair have fuses that are far in excess and have not afforded any protection to the motor or electronics....
I did not make my recommendations on a whim, there is evidence from other forums, that members there have had the same recommendation from a major machine tool supplier....
At the end of the day, its no skin off my nose if the op does nothing..however, if I carry out repairs to a machine, I ensure that the equipment fuses are adequate and fit for purpose in order tomoffer any guarantee of repair.

Rant over....
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Offline PekkaNF

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Re: poorly seig c3
« Reply #32 on: June 08, 2017, 04:07:13 PM »
Something lost in translation :wave:

My intention was not to criticize your choice of fuse on this particular instant. Merely to point out some points to greater public that there is some logic on fuse selection.

I have noticed the same thing about fuse size, maybe they rather sell new card/motor than listen rap about burnt fuses. Also the mill might not reach rated power with smaller fuse, but there is risk of burning something under other circumstances.

Cheers,
pekka

Offline tom osselton

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Re: poorly seig c3
« Reply #33 on: June 09, 2017, 12:44:56 AM »
That happened to me on my Craftex mill the doughnut wire wrapped thing (choke?) unsoldered itself and dropped onto wires below! They gave me a different board but the tack has not worked since.

Offline bpud

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Re: poorly seig c3
« Reply #34 on: September 06, 2017, 07:03:18 PM »
I've only just caught up on this thread.  My Sieg C3 had a very similar problem.  A short time after getting the lathe about 11 or 12 years ago the plastic chuck guard was removed, it got in the way all the time.  The switch and metal guard mounting rod were left in place.  Sometimes the rod needed a bit of a tweak to ensure that the switch was open and the motor would run.  The chuck guard microswitch was a bit hair trigger, so it was removed and a small wire link applied to the PCB.  End of problem!!
cheers
Bill

Offline PK

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Re: poorly seig c3
« Reply #35 on: September 06, 2017, 08:17:08 PM »
The problem with specifying a fuse is that it has to:
a: blow at a current * time value (it's energy that blows a fuse, not current)
b: withstand the inrush current at startup. which can be 10-100 times the operating current if you have a DC power supply (like those little lathes do)

For a circuit that always draws the same current, you fix this with an NTC thermistor.  This device has a high resistance when cold and this resistance drops as it heats up. What happens is that the high resistance limits the inrush current at startup to sane values (maybe only 4 -5 times operating current) and then heats up.

For a circuit that draws a variable amount of current (eg a motor speed control on a lathe) it's somewhere between VERY hard and impossible to pick an NTC thermistor with the correct characteristics.

So what do you do?
The cheap way is to pick the smallest fuse that has an INRUSH rating up to the task and just live with whatever its maximum continuous rating is.

We went through this process recently where a product did, in fact, draw a fairly constant current of about 100mA at 220V. However it needed to operate from 24V-250V.  As such it had a big bank of capacitors (to deal with the low voltage application). We measured  inrush at around 150A when we ran from 250VAC...