Sieg sc4 emergency stop switch

GreatOldOne

GreatOldOne

R'lyeh Engineering Works
H-M Supporter Gold Member
Joined
Mar 20, 2014
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418
Hi Guys,

The emergency stop switch has stopped working on my lathe. I’ve taken the physical switch out of the front panel, and checked it for continuity with my multimeter, and it works fine. So something is up further down stream, on the control board.

I’ve googled the issue, and have seen others have experienced the same problem - but the only solution I’ve found is to replace the entire control board... which seems a bit much, considering the lathe works perfectly fine in all other regards.

Has anyone else had this issue? I’m assuming a burnt out component on the board, which I’m willing to hunt down and replace, but If someone else has already got a solve for it, I’d rather not go through lots of probing and schematic noodling if I don’t have to.

cheers

Jason
 
Sounds like this really doesn't qualify as a true "emergency stop switch" since it shouldn't depend on some fussy (possibly cmos) electronics to stop the machine. Anyhow, you really would need to find a schematic or at least reverse-engineer the board to some extent to fix it.
Personally I would add a latching contactor on the mains feeding the board, controlled by the switch to give a true positive cutoff- assuming the control board works otherwise
-mark
 
Hi Jason,

I have an LMS 5500 bench lathe, which is a Sieg SC4 with some customization and a blue and white paint job. It has an internal contactor that is closed to power up the machine when the E-stop is in reset position. When the E-stop is pressed, it deenergizes the contactor coil and the contactor opens, cutting off power to the rest of the machine. The tach readout goes dark and nothing works until the E-stop button is twisted to reset it.

Since your E-stop switch tests okay but is not killing power to the machine as it should, the contactor could be hung in the closed position. There are a number of things that could cause that but I won’t go into that yet. I suggest as a test, reinstall the E-stop if you haven’t already, press it in and make sure it latches in the stop position, as if E-stopping the machine and leave it, don’t reset it. Then plug the machine in and flip the main power rocker switch to “on”. You should hear the hum of the cooling fan for the electronics and the green light should come on, but everything else should be inoperative and the tach should still be dark. If all of this is true so far, the contactor is open as it should be. If the machine is operable at this point, the contactor is closed when it shouldn’t be. To see if it is hung up in the closed position, unplug the machine or flip the power switch off while listening closely for a “click” from inside the control box. If you hear a click, the contactor is probably okay and there is something else wrong in the control circuitry, maybe the board that you referred to. I would try this test before I tore into the circuit board if you haven’t already. Hope this helps. Sorry for the long windedness. (Is that a word?)

Tom
 
Higgite is right, you should try to determine if there is a physical contactor or relay on the board- a visual would help
If there is a small relay it may be hard to hear the click
I have never experienced a relay stuck in the closed position but it is possible- just a really long shot
 
markba633csi said:
Higgite is right, you should try to determine if there is a physical contactor or relay on the board- a visual would help
If there is a small relay it may be hard to hear the click
I have never experienced a relay stuck in the closed position but it is possible- just a really long shot
Click to expand...

If you put the disconnecting switch before the plug, you won't have to debug the circuitry.
Hit the switch and the whole lathe goes to zero power.
 
So, I spent the last couple of hours taking the lathe control board out to take a look at it. The E stop button cuts the line voltage to the external socket on the back of the headstock, and also cuts a 12v dc signal line.

tracing this back to the inputs on the board, and then via the traces on it - it’s exactly as @higgite says above. The signal voltage energises the coil on a relay closing the line voltage contacts - hitting the e stop button cuts power to the coil and the normally open relay should return to open. Only it doesn’t. Here’s the culprit

63222748-1A1A-4CDD-B3EA-D1D36100F124.jpeg


From my Googling, it would appear that these things are a couple of quid each ($3, C$6, 2€, 1 New Republic Credit, 5 Imperial Scrip, 20 Quatloos). I’ll order one and replace it, and see if that fixes things.
 
it is just a simple single pole relay.
you could remove the faulty relay and remotely locate another relay if you so desired, you could use a larger relay too!
coil voltage is 220v, go for a 30 amp @240VAC rating and you'll be just fine
 
All fixed. Of course, because I ordered a replacement relay the damn original one started working again. I must have jarred it loose when I was removing the control board. It must just have gotten hung up, rather than the contacts welding themselves together. :rolleyes:

Ah well - at least I have a spare on hand, and didn’t have the pain of desoldering the original relay from the board. :p
 
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