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PUK2 visor auto dimming problem


#1

Hello all.

To those of you that have or have had a PUK 2 welder, have you had
any problems with the light/auto dimming eye protection not dimming
when the arch fires? Mine was working then on the next firing, I SAW
A REALLY BRIGHT LIGHT for a day or so. Any quick fixes next to me
sending the unit back to the manufacturer?

All advice is apprieciated.


#2

Hi Christina:

I’ve got a PUK3, but mine’s rigged up with a secondary shutter
instead of using their dedicated microscope with the built-in
shutter. (I already had a spare stereo 'scope, so I thought I’d save
a few bucks… Really bad idea.)

Anyway, I suspect my shutter is probably a scaled down version of
yours, and as I’ve had to pull mine apart to frankenform it into
something useful, I’ll share what little I know.

My shutter (and yours, probably) is just a little LCD filter that
flicks opaque when it gets a small DC charge. They’re the ‘auto
darkening’ filters that you get from the welding supply place to put
into a welding helmet. Those use solar panels to pick up enough power
to trip the LCD’s into the opaque setting, and a little optical
sensor to trigger the system when the welder fires. My microscope
shutter is just the LCD filter from one of those, repackaged with a
connector wire to the PUK to trip it. I suspect yours is probably
the ‘full face’ version, in a frame. When I was trying to make mine a
little more useful, I tried one of the welding shields. While it got
plenty dark enough, the response time wasn’t nearly fast enough to
prevent a close up view of the VERY BRIGHT arc. Yeouch! (Only
tried that experiment once…)

This is one of those good news-bad news things.

Good news: the filter’s a very simple system. Check the contact wires
where they hook into the PUK. Make sure they’re clean and seated
right.

If it still doesn’t trip, get a volt-meter and start checking to make
sure the PUK is sending a trigger charge down the line. (pull the
cord, and start feeling out the connections (With the volt meter!) to
see which pair goes DC high when the welder fires. (The PUK 3 has far
more pins on that connector than it needs. Unknown if the PUK2 is
equally profligate, but it seems likely.) I never had to suss out
what the ‘opaque’ charge for the LCD is, but I doubt it’s much. 5VDC
max, probably much less, if it’s getting sustained power from small
solar panels in its welding helmet incarnation. Anyway, you’re
looking for a voltage spike across two of those pins when the welder
fires. So long as you’re getting something there, the welder’s doing
its bit, and the problem’s with the filter. If you don’t get a spike
across any of those pins, call Lampert, as its likely to be the
welder. If you do get a trigger charge from the welder, then it’s the
filter. Unfortunately, the filter’s pretty stupidly simple. Makes it
hard to break, but nearly impossible to fix once it does. The only
thing that might remotely be fixable is if one of the lead wires has
come loose from the LCD sandwiched between the two layers of the
glass filter. If you’re good with a soldering iron, you might be
able to resolder that. The other thing that might be doing it is if
the cord got kinked somewhere, and the wires broke in the cord. Use
your volt- meter to check for continuity between the pin-sockets on
the end of the wire and the two little teeny wires soldered to the
LCD filter sandwich. To do that, you’ll have to very carefully
disassemble the filter frame. Be very careful not to jiggle the
little wires attached to the filter, they’re very fragile. If you
don’t get continuity between the end of the cord, and the wires
attached to the filter, it’s the cord. Not easy to replace, but
easier than the filter. If you’re getting continuity all the way to
the filter itself, it’s the filter, and that’s probably unfixable
short of sending it back to Lampert.

If you get to the stage of thinking about pulling the filter frame
apart, you really want to call Lampert first to see if they have any
better ideas.

Regards,
Brian Meek.


#3

Hi Gang,

One of the problems building your own ‘welding shield’ for a PUK or
pulse arc welder is the response time of the sensor & the filter.

The response time of welding helmets used in arc welding is
typically about 1/20,000 sec. While this is fast enough for a
continuos arc used in arc welding, it’s much too slow for the single
shot arc used in the welders such as the PUK or ABI & others. By the
time the sensor has detected the flash the filter has darkened, the
flash is done. Typically, welders close their eyes when they
initially strike the arc & open them after the arc has started.

I’ve not investigated it, but my guess would be that the control
unit of the PUK & similar welders has a circuit that fires the flash
filter the necessary time before the arc so that the filter is dark
when the flash occurs.

The only solution I can think of if you don’t have a unit that
automatically triggers the filter is to close your eyes before you
step on/press the trigger for the arc.

Dave


#4

Hi Dave:

Yeah, that’s pretty much exactly what my experiment bore out: the
firing circuit isn’t nearly fast enough. The response time on the
one I tested was about 50 milliseconds, and that’s still way too
slow. I’ve taken a PUK shutter apart. The guts of it are the LCD
filter unit from a welding helmet shield, wired directly into the PUK
for both power and triggering.

I didn’t have to get any further than that to get mine modified to
the point where I was happy enough with it, but what it looks like is
that since the PUK knows when it’s about to fire, it triggers the
shutter a few milliseconds ahead of the welding pulse. Quick, simple
and easy. (so long as you’re reading the PUK’s mind.)

If you really needed a bigger shutter, you could probably tickle out
the PUK’s pin-out for that connector, and build something that’d
accept the PUK’s triggering signal, which would solve the timing
issue. In aid of that, (before I gave up) I took my shutter to the
local ‘serious’ electronic geek supply place. No joy at all finding
a connector that’ll mate to whatever that connector on the back of
the PUK might be. It’s a Euro/DIN connector of some flavor, but god
only knows exactly what. Even in the supply catalogs we couldn’t find
anything that’d work. So it won’t be the easiest hack ever
attempted.

I’ve tried the ‘close your eyes’ technique. Not such a hot idea.
Eventually, you will forget… Annoying if using it bare eyed.
Major problem if you’re on a scope.

(Not to say I don’t do it for objects where I can’t fit it under the
scope, but I’m always careful.)

FWIW,
Brian.