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Old September 11th, 2019, 07:01 AM   #16

wimpiesplc is offline
Join Date: Feb 2012
Location: Netherlands
Posts: 344
Originally Posted by kalabdel View Post
I took apart an S7-200 to have a look at the POTs and you should be able to get any electronic repair shop to replace them for you. Very easy soldering and the POTs are dime a dozen.
my first question was, and even more seeing these pics, how does a pot break off the circuit board?
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Old September 11th, 2019, 10:28 AM   #17
United States

Busch is offline
Join Date: Sep 2019
Location: Illinois
Posts: 4
The POT was used for temperature control of a plastic welding mechanism (hot knife) for plastic banding straps. Now with the POT broke off the board the hot knife will not get up to temp to weld the straps together. Hence the no output. Maybe I am just wording things differently IDK.

All other functions are working as they are supposed to. It is just this area that is not working as it is supposed to. Because the POT for the hot knife is broke off of the board.

After contacting Signode (the manufacturer of this machine) and telling them what has happened (and of course after I myself went through the diagnostics book) we came to the conclusion that the hot knife is not working because that POT is what controls it.
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Old September 12th, 2019, 02:55 AM   #18
United Kingdom

parky is offline
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Join Date: Oct 2004
Location: Midlands
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Maybe a quick fix would be to put a small temperature controller on it and enable it with a signal from the PLC for example a spare contact off the safety relay or another relay that is energised when system is ready, however, there could be an interlock in the PLC that stops operation until unit is up to temperature but this would require an analogue input to the PLC, this could be overcome be it analogue feedback (temp sensor with analogue output to feed back) or if a digital one a contact off the temperature controller is up to temperature.
This might be a cheaper option.
I would be careful about dismantling the PLC just in case this would disconnect any battery used for backup, not familiar with the 1200 range it could be a battery less unit, in which case there should be no problem.
However if you decide to bite the bullet & buy a programmed unit from the supplier then you could try to repair the other, try & get the code uploaded & keep it as a spare.
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