fixing the EconoTig
Geo. Dubovsky
start and all foot-pedal control in GTAW mode. Stick is ok and I can
scratch start TIG in ac and dc switch positions, but when the arc
starts, it is at full current. The switch in the foot pedal seems to
cause all of the relays and gas solenoid to kick in ok, just the
rheostat has no control. I think the sig is getting back to the
control board ok.
Does anyone have a schematic or functional block diagram of the
control board, Miller P/N 153385? It seems to have mostly common
electronics on it, so it oughta be fixable (or at least understandable
enough to know how much trouble my wallet is in!)
I went to the Miller web page, but they don't seem to want folks to
talk to them directly, just to authorized service depots. I am in
central VA, and the only depot listed for VA is near DC. Thanks.
geo
brad
the foot pedal completely overides the panel rheostat (not the contactor or
on/off switch)to give the operator current control. Most use a combination
of panel and pedal rheostats to give the current control.I will check this
out,as I am sure I have a shop manual around here somewhere.From what you
describe it appears that the pedal rheostat has gone south. More testing is
definitely in order. I'll get back tomorrow after I've had a chance to look
at the diagrams.BTW-I really haven't worked on a lot of econotigs-seems like
a very good machine with few troubles. Good Luck-brad
Geo. Dubovsky wrote in message <37b869b8...@News.inmind.net>...
Kristian Ukkonen
> I have a '93 vintage Miller Econotig that has lost both high-voltage
> start and all foot-pedal control in GTAW mode. Stick is ok and I can
> scratch start TIG in ac and dc switch positions, but when the arc
> starts, it is at full current. The switch in the foot pedal seems to
> cause all of the relays and gas solenoid to kick in ok, just the
> rheostat has no control. I think the sig is getting back to the
> control board ok.
Just a very simple idea (I have no experience of Miller welders):
Usually the foot-control uses a switch to signal the welder to start
welding cycle (which works in your case) and a adjustable resistor
(rheostat) to adjust the current. It is possible that there are three
connections to resistor (two ends and brush) or just two (one end and
brush)
Now this requires 4 or 5 wires going to TIG welder from foot control.
Now you take your multimeter, switch it to resistance measurement
and check which pin is which on the connector fron foot control.
Two pins have to be infinite-resistance/close-to-zero depending on
whether the control pedal in pushed in or not (just a switch) and
2/3 other pins should have resistance value changing depending on
how much you press the pedal.
So, if you don't get action like that, it is possible that the
resistor is damaged. If the welder uses voltage signal (0..10V or
something) for controlling welding current, normally there
goes 0V and 10V to ends of resistor and the signal is taken
between 0V and brush. If brush have damaged, it is possible that
it is always at 0V (open-circuited really) and if that is full
current (10V would be zero current then), you'd get full current
always. If the welder uses current signal (0..20mA or something)
then things might be different - A big-valued resistor in series
to limit current or something - and open-circuit would cause
infinite resistance and zero current, which might be the signal
for full current.
So check the foot control. Replace the rheostat if it is broken.
They cost about 1-2 usd at any electronics component store.
Check that you get same value (ohms) and either linear or
logaritmic (same as the old one).
If that does not help - check the connector between welder and
foot-control. Clean the connector and the pins. Measure that the
connection is ok.
After this you can be pretty certain it is the welder that has
the problem.
Check how the welder select whether to use welder panel
rheostat or foot-control rheostat. Perhaps this selector
switch is broken? Measure with ohm-meter that it works.
It might be some design like that the foot-control connector
has two extra pins that are short-circuited at the
foot-switch side connector, and when you connect the
foot-switch these pins get connected and current flows
throught them (and relay coil) pulling a relay somewhere, and
thus "automatically" switching remote-control signal input
from welder-panel-rheostat to remote-control-rheostat.
This relay/circuit might be broken?
The common way for PWM ICs to control duty-cycle
is to have a voltage signal (0..5 V) to some pin. This is how
current is set in these welders (usually - the design may be
different in your welder). So next check where the wires from
foot-control connector go, and check that the connections are
ok (the wire has a connector to PCB somewhere). There might be
some isolation device between foot-control and IC (optoisolator
or something). The PWM chip eventually gets the signal. Check
that the signal value changes as you press the foot-pedal. If
it does, then the PWM chip is broken when it doesn't adjust
duty-cycle (welding current). Very, VERY unlikely though. You can
get data-sheets for these ICs (and optocouples) from manufacturers
webpages (UC for unitrode at www.unitrode.com etc.) so you can see
where the remote-control signal should come. Note that the same
signal should change when you adjust current without foot-control
from welder panel - so if the normal adjustment works from
rheotstat at welder panel, the PWM chip works ok.
Don't try to debug the circuits inside the welder if you
don't know what you are doing.. You have to measure things
with voltage on, and there are potentially hazardous voltages
present. However, you pretty much can't destroy anything
by just measuring voltages.
I think the reason why they don't list things like this (or
schematics) in manuals is that they can sell their foot-controls
at totally outrageous prices. Esab foot-control costs 1000usd here.
Even the simple single-rheostat-in-box-with-cable-to-welder
remote control costs 300usd. I do understand that companies have
to make profit, but still.. I _really_ like using the Esab
Aristotig 250 ac/dc welder though (but without foot-control until
I find a used one at reasonable price, or build one). Anyone with
an extra one?? :)
Just ideas,
Kristian Ukkonen.
Geo. Dubovsky
I have rung out the wiring from the foot pedal to the control board;
there are two wires for a switch (they do their switch thing just
fine, apparently) and three wires from a 1k potentiometer. Only two of
these wires are used, one end of the pot and the wiper. This variable
resistance sig is getting to the control board ok, so the problem is
probably in the board.
I am the original owner of this machine and I have all of the manuals
that Miller provided; details of the control board are simply not
included. It is shown as a dotted outline with interconnect details -
no schematic. I am a semi-ancient EE (I had to use a sliderule in
college, but I am not yet eligible for Social Security) and I have no
problem working around kilovolts or tens of kilowatts. But I need a
roadmap, dammit!!:)
If someone has any info on this board, they will save me from throwing
myself at the mercy of the service depot, or at least save me from
having to generate my own schematic from the double-sided board - ugh.
Thanks for all the suggestions.
geo
On Mon, 16 Aug 1999 19:58:28 GMT, g_dub...@ats-forest.com (Geo.
Dubovsky) wrote:
>I have a '93 vintage Miller Econotig that has lost both high-voltage
>start and all foot-pedal control in GTAW mode. Stick is ok and I can
>scratch start TIG in ac and dc switch positions, but when the arc
>starts, it is at full current. The switch in the foot pedal seems to
>cause all of the relays and gas solenoid to kick in ok, just the
>rheostat has no control. I think the sig is getting back to the
>control board ok.
>
Ned Simmons
The lack of documentation of the board itself seeems to be standard
practice. I went thru the same thing on my Airco. It was a matter of
either replacing the board or wading thru the repair with no schematic.
I was lucky. It turned out to be a shorted diode on the board which was
easily detected with a DMM. I'd say it's worth going over the board for
the easy stuff first.
BTW, I'm quite sure the damage was caused by someone setting the output
of the hi-freq too high. Nice Tesla coil right next to a board full of
electronics.
A replacement board was about $80 IIRC.
While I've got your attention, does anyone know who actually made my
Airco Heliwelder V ?
Ned Simmons
Jim Stewart
>
> An update:
> I have rung out the wiring from the foot pedal to the control board;
> there are two wires for a switch (they do their switch thing just
> fine, apparently) and three wires from a 1k potentiometer. Only two of
> these wires are used, one end of the pot and the wiper. This variable
> resistance sig is getting to the control board ok, so the problem is
> probably in the board.
>
> I am the original owner of this machine and I have all of the manuals
> that Miller provided; details of the control board are simply not
> included. It is shown as a dotted outline with interconnect details -
> no schematic. I am a semi-ancient EE (I had to use a sliderule in
> college, but I am not yet eligible for Social Security) and I have no
> problem working around kilovolts or tens of kilowatts. But I need a
> roadmap, dammit!!:)
>
> If someone has any info on this board, they will save me from throwing
> myself at the mercy of the service depot, or at least save me from
> having to generate my own schematic from the double-sided board - ugh.
>
Hi, Geo - I have an Econotig and was about to dig out the diagram.
Guess I won't. (BTW, I also used a sliderule in college, not yet etc.
etc.)
You know as well as I that you *can* draw the schematic, it's just a
double-sided board. Go ahead. This exercise builds character.
(Whattaya mean you already have plenty?)
(When you're done, can I have a copy? Heh, heh...)
-js
--
Ernie Leimkuhler
<br...@microconnect.net> wrote:
> As I remember the econotig is somewhat different than most. It seems that
> the foot pedal completely overides the panel rheostat (not the contactor or
> on/off switch)to give the operator current control. Most use a combination
> of panel and pedal rheostats to give the current control.I will check this
> out,as I am sure I have a shop manual around here somewhere.From what you
> describe it appears that the pedal rheostat has gone south. More testing is
> definitely in order. I'll get back tomorrow after I've had a chance to look
> at the diagrams.BTW-I really haven't worked on a lot of econotigs-seems like
> a very good machine with few troubles. Good Luck-brad
> Geo. Dubovsky wrote in message <37b869b8...@News.inmind.net>...
The first generation Econotigs had this setup, but the second generation
reactivated the dial for max power control.
> >I have a '93 vintage Miller Econotig that has lost both high-voltage
> >start and all foot-pedal control in GTAW mode. Stick is ok and I can
> >scratch start TIG in ac and dc switch positions, but when the arc
> >starts, it is at full current. The switch in the foot pedal seems to
> >cause all of the relays and gas solenoid to kick in ok, just the
> >rheostat has no control. I think the sig is getting back to the
> >control board ok.
> >
> >Does anyone have a schematic or functional block diagram of the
> >control board, Miller P/N 153385? It seems to have mostly common
> >electronics on it, so it oughta be fixable (or at least understandable
> >enough to know how much trouble my wallet is in!)
> >
> >I went to the Miller web page, but they don't seem to want folks to
> >talk to them directly, just to authorized service depots. I am in
> >central VA, and the only depot listed for VA is near DC. Thanks.
> >
> >geo
--
STAGESMITH PRODUCTIONS
Custom Metal Fabrication
ABANA AWS IATSE Local 15/488
Renton, Washington, US
Ernie Leimkuhler
(Ned Simmons) wrote:
This was posted a while ago, and may help.
> > Airco welders
> > with serial numbers starting with two letters
> > and followed by 6 numbers are made by miller.
> > the two letters tell the year of manuf. A=0,
> > B=1 and so on. the letter I is skipped so that
> > HJ=1978. in early 70's they used 70-xxxxxx that
> > was 1970. prior two the 70's they had one
> > letter instead of two.
best of luck
--
STAGESMITH - Custom Metal Fabrication - Renton, WA, US
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