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Posted by xray on July 10, 2007, 4:05 am
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wrote:
>The problem description sounds EXACTLY
>like a "dirty" pot.
It's not a pot. The same problem is being discussed in
sci.engr.joining.welding . I replied there as I have the same welder
with the same general problem.
It's not a pot because the knob can be turned forever in either the
clockwise or ccw direction, and when it goes wierd and the current
display makes a big jump it then tunes around that new value.
So I think there must be an input device connected to the knob with some
kind of digital pulse output, probably an optical encoder. My PT 185 is
very lightly used and shows a bit of the same problem. My guess is some
kind of design problem from the factory either with the input device or
noise/debounce handling. The problem I see on mine is not bad enough yet
to make me dig inside and try to figure out what is happining.
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Posted by Phil on July 10, 2007, 4:27 pm
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I sent a mail to Lincoln and am waiting for an answer , that's correct it
isn't a POT as in the older welders , I opened the thing up and looks like
the Optical Interrupter is encased in Epoxy , I may jus forget about the the
original Optical Unit and replace it with a 555 IC Pulser with an UP/ DOWN
button , Lincoln will probably want to swap the PC Board and I would end up
with the same problem at a later date , hard to win , I have a local dealer
that swears by Lincoln , I have a Miller TIG/STICK that is over 30 yrs. old
and they gave me detailed schematics and it can be serviced by ME , Thanks
Again .
> wrote:
>
>>The problem description sounds EXACTLY
>>like a "dirty" pot.
>
> It's not a pot. The same problem is being discussed in
> sci.engr.joining.welding . I replied there as I have the same welder
> with the same general problem.
>
> It's not a pot because the knob can be turned forever in either the
> clockwise or ccw direction, and when it goes wierd and the current
> display makes a big jump it then tunes around that new value.
>
> So I think there must be an input device connected to the knob with some
> kind of digital pulse output, probably an optical encoder. My PT 185 is
> very lightly used and shows a bit of the same problem. My guess is some
> kind of design problem from the factory either with the input device or
> noise/debounce handling. The problem I see on mine is not bad enough yet
> to make me dig inside and try to figure out what is happining.
>
>
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Posted by Jon Elson on July 11, 2007, 12:51 am
Please log in for more thread options Phil wrote:
> I sent a mail to Lincoln and am waiting for an answer , that's correct it
> isn't a POT as in the older welders , I opened the thing up and looks like
> the Optical Interrupter is encased in Epoxy
Are you sure it is an optical encoder? I'm wondering if it is
one of the very cheap mechanical encoders, they have a printed
wheel with the quadrature pattern and brushes like inside a pot
to make contact with the wheel. After the contacts get dirty,
they get intermittent. If it is a mechanical encoder, you
should be able to detect the contacts opening and closing with
an Ohmmeter. One clue is most mech. encoders will only have 3
wires, the optical ones will have to have at least 4.
You could probably patch in a better-quality optical encoder if
the above scenario is correct.
Jon
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Posted by Phil on July 14, 2007, 9:22 pm
Please log in for more thread options I will have to take a second look at the PC board Jon , my experience has
bee mostly with Optical and have not used the mechanical type , will get out
the OHM meter and check it out , it looks like a small POT and it does have
3 pins going to the PC board , I have made pulsers that can trigger UP or
DOWN , will try to find something better than the original junk , Thanks Jon
.
> Phil wrote:
>> I sent a mail to Lincoln and am waiting for an answer , that's correct it
>> isn't a POT as in the older welders , I opened the thing up and looks
>> like the Optical Interrupter is encased in Epoxy
>
> Are you sure it is an optical encoder? I'm wondering if it is one of the
> very cheap mechanical encoders, they have a printed wheel with the
> quadrature pattern and brushes like inside a pot to make contact with the
> wheel. After the contacts get dirty, they get intermittent. If it is a
> mechanical encoder, you should be able to detect the contacts opening and
> closing with an Ohmmeter. One clue is most mech. encoders will only have
> 3 wires, the optical ones will have to have at least 4.
>
> You could probably patch in a better-quality optical encoder if the above
> scenario is correct.
>
> Jon
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>like a "dirty" pot.