AL spoolgun stuck on high

Karl Townsend wrote:

Didja try the gambits offered in the Owner's Manual
on page 16?
www.millerwelds.com/om/o1308n_mil.pdf

Low, high, or erratic wire speed.
   Readjust front panel settings (see Section 3-1).
   Place Low Range/Full Range switch in correct position (see Section 3-1).
   Change to correct size drive rolls (see Section 4-5).
   Readjust drive roll pressure (see Section 2-12).
   Replace inlet guide, contact tip, and/or liner if necessary (see Sections
4-4, and 4-8).
   Check position of input jumper links (see Section 2-9).
   Have Factory Authorized Service Agent check main control board.

--Winston

wrote:


4-4, and 4-8).

Probably good to point out the basics. I hadn't double checked the
input jumper. Its OK

Karl Townsend wrote:

(...)


Suspect a broken wire or open connection between RC4-4
and the pot on the gun.

Advise photograph existing wiring, unplug and re-plug
connections.  Please consider good quality contact
cleaner treatment of connectors, too.

--Winston

wrote:


Good suggestion. I'll get some contact cleaner and try this.

Karl Townsend wrote:

LPS or better.  Not Radio Shack brand!

:)

--Winston

On Thu, 04 Aug 2011 11:50:52 -0500, Karl Townsend


Maybe blown SCRs. See what they measure anode to cathode (and with
leads reversed) on a multimeter using the diode (ohms) range. With
power disconnected, obviously, or the meter will be smoked.

On Thu, 04 Aug 2011 13:24:06 -0400, Spehro Pefhany


You'll have to dumb this way down for me.

On Thu, 04 Aug 2011 13:12:09 -0500, Karl Townsend


I also should point out the standard gun works fine. If I follow the
prints right it uses the same SCR??? to control wire feed speed.
Please know, I can hardly read a print.

Karl

On Thu, 04 Aug 2011 13:12:09 -0500, Karl Townsend


Is there a part marked Q1 on the PCB that is connected to the motor
terminal (59) ?  That should be a 10A SCR if I got the right
schematic.

On Thu, 04 Aug 2011 14:28:16 -0400, Spehro Pefhany


No sign of smoke by this device. The are four pins on Q1 so I did ohms
both ways (a diode gives different reading depending on which way)
accross each pin:

top pins gives 144 K ohm
bottom pins 137 K ohm
right side 0 ohm
left side 6.1 K ohm


You must have found a more complete schematic than I have. Where did
you find it?

Karl

On Thu, 04 Aug 2011 14:32:29 -0500, Karl Townsend


I'm guessing it's similar to the Snap-on 250A welder:

www.800abcweld.com/pdf/mm250sl_service_manual.pdf

    As wired (based on the schematic you posted the URL for) this is
not a rheostat, but rather a potentiometer.  (I expected that because
rheostats are seldom that high in resistance, but I had to check the
schematic to be sure.)

    The difference between a pot and a rheostat is that a pot uses
all three terminals to divide a voltage to an variable output.  A
rheostat is in effect only a two terminal device -- a variable resistor
used between two points (though sometimes the CCW end will be connected
to the wiper to minimize how high the resistance shoots when the wiper
makes poor contact.)  And because a rheostat is usually (though not
always) running with more current, it will frequently be constructed as
a wirewound on ceramic instead of the carbon resistance track common
with pots.

    So -- did you check all three pins?  It should be 10K between
pins 50 and 51, and pin 30 should measure resistance to the two other
pins which add up to a total of 10K.  I suspect that pin 51 is not
making connection, so you will get full speed all the time.  They don't
say, but I expect that you should measure 10V DC (though it may be 5VDC
or some other value) between pins 50 and 51 at the pot.  With the
voltmeter connected between pin 51 and the wiper of the pot (pin 30) you
should get a voltage which varies as you turn the pot from fully CCW to
fully CW.


    The one marked IPM (which I presume is "Inches Per Minute")?  I
wasn't sure at first whether you were talking about the drawing as it
popped up in the PDF reader or after rotating so the lettering on the
drawing was right side up.


    Check the full connection of all three points of the pot to the
control.

    Good Luck,
        DoN.

--
                  Remove oil spill source from e-mail
          (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
           --- Black Holes are where God is dividing by zero ---

DoN. Nichols wrote:

(...)


Apparently that circuit works fine.
Karl mentioned that the local controls work properly when the
spoolgun interface is not connected. That is, just using the
built-in wire feeder and IPM pot you cited.

We still both hypothesized the same thing. If there were a break in
Circuit 33, RC4-4, then the welder would be commanded to go to
full speed all the time when the spoolgun was connected.


If there was a way to check those connections at the
welder control board, that would be very interesting
information indeed.  Either way, it could not hurt to
disconnect the control board and wash down the connectors
with some good quality connector cleaner.  LPS!

--Winston

Thanks DoN and Winston. I'll check all this out.

Karl

Karl Townsend wrote:

Please keep us posted, Karl.

--Winston

wrote:


VICTORY!!!

Well, sort of. The female amphenol plug is the loose connection. I ran
a drill bit in/out to remove swarf and dirt. Then sprayed BrakeKleen.
Put plug on real tight. It works. My solution for now will be to put a
bracket on the side of the welder to hold all the spoolgun cable. Then
never take the connection apart again.

Failing that, I'll hire somebody to re-solder on a new amphenol plug.

Karl

Karl Townsend wrote:

YeeHaw!  :)

--Winston

    Great!


    Out of curiosity -- is the plug fitted with soldertail pins or
crimp pins?

    And is the female connector on the panel or the spool gun?

    It is a good idea to tie a plastic baggie around the connector
when it is not plugged into the panel.

    Good Luck,
        DoN.

--
                  Remove oil spill source from e-mail
          (too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
           --- Black Holes are where God is dividing by zero ---

wrote:


Soldertail. I don't do this.


On the panel.