Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

You haven't mentioned much about what or how he's welding except that it
involves a wire feeder, but if he is using solid steel wire with gas shielding,
he could be losing the shield from either an electrical or mechanical problem.
That will give a sputtering, bubbly and ugly weld.

You may need to answer a few of the following to get more specific help.

Is it mild steel or aluminum, you are welding?
Are you using solid wire, flux core?
Are you indoors or out in the wind?

Before you go too far with the hard stuff, check out the obvious. You need a
steady flow of shielding gas for welding with solid wire. Too fast of a rate can
cause suction of air into the flow. Clean metal helps a lot.

There are others that frequent this newsgroup that can probably be more
helpful but I have a couple of suggestions. If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections. If not
they can easily heat up and cause problems. Also, have you checked that the
wire is feeding smoothly? If it's skipping or hanging up in the liner it
can cause problems.

Also, if he's using gas make sure he has consistent flow.

Best Regards,
Keith Marshall


"The universe is full of magical things,
patiently waiting for our wits to grow sharper."
-Eden Phillpotts, A Shadow Passes, 1934
"Alex Wiecek" wrote in message
om...
Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

"Keith Marshall" wrote in
:

There are others that frequent this newsgroup that can probably be
more helpful but I have a couple of suggestions. If you haven't
already checked, make sure the gun and the ground cable have firm,
clean connections. If not they can easily heat up and cause problems.
Also, have you checked that the wire is feeding smoothly? If it's
skipping or hanging up in the liner it can cause problems.

Also, if he's using gas make sure he has consistent flow.

Best Regards,
Keith Marshall


"The universe is full of magical things,
patiently waiting for our wits to grow sharper."
-Eden Phillpotts, A Shadow Passes, 1934
"Alex Wiecek" wrote in message
om...
Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has
a solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the
real test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for
processing. So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex




Alex i had the same problem at work the voltage was fine then it would
change five volts next time i put down the weld. It turn out to be the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is 20
volts. I dont know if this helps. im dont work on welding machines but i
do know what happen to me.


shipyard worker

On Tue, 16 Sep 2003 07:36:43 GMT, mylo wrote:

On 15 Sep 2003 18:55:57 -0700, (Alex Wiecek)
wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

Check voltage on contactor, line and load side!

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

check ground to work piece

IIt could also be a bad roll of wire!
if the wire is solid and not flux core it could be the gas solenoid!
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Oh, almost forgot , you want to keep the proper distance from the work
piece! I added that because you did'nt indicate whether he was an
experienced welder! I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

On 15 Sep 2003 18:55:57 -0700, (Alex Wiecek)
wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld



sounds simple bit check the welding wire for rust or feed problems
doug

Hello everyone...

First of all, I'd like to thank each and every one of you for taking
your time and advising me as to which direction to take to tackle this
problem.
In order to alleviate any confusion, I thought I'd come up with one
reply and address all your questions.... here it goes..

Zorro writes:

You may need to answer a few of the following to get more specific
help.

Is it mild steel or aluminum, you are welding?
We tried both.

Are you using solid wire, flux core?
Mmmm... I don't know.

Are you indoors or out in the wind?
Indoors.


Keith Marshall writes:
If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections.
If not
they can easily heat up and cause problems. Also, have you checked
that the
wire is feeding smoothly? If it's skipping or hanging up in the
liner it
can cause problems.

From what I could tell, the wire is feeding smoothly. He would know
better and I'm sure he'd see it first as he is a proffessional welder.

Also, if he's using gas make sure he has consistent flow.

This suggestion came up a few times. I'm trying to remember whether or
not he tried using a different tank. But I will check this next time
I'm in his shop.


Shipyard Worker writes:

Alex i had the same problem at work the voltage was fine then it
would
change five volts next time i put down the weld. It turn out to be
the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it
will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is
20
volts. I dont know if this helps. im dont work on welding machines
but i
do know what happen to me.

One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.


mylo writes:

Check voltage on contactor, line and load side!

The contactor is at the back of the unit? Or are you talking about the
power switch?

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

I'm sure he would have noticed it. He is a very experienced welder.

check ground to work piece

Good idea.


IIt could also be a bad roll of wire!

We tried three different rolls....

if the wire is solid and not flux core it could be the gas solenoid!

This suggestion came up a few times... hmmmmm...
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Well.. apparently he used another welding machine on the same circuit
and it worked fine for him.

I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?
I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate
it.

Alex VE3GOP

Alex Wiecek wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

This sounds to me like you've got either an obstruction in the regulator
or the tank valve isn't allowing adequate flow.. it sounds like the
shield gas is accumulating in the system but the reg. isn't supplying
enough volume, it's not keeping up with the demand. It recovers between
attempts to weld and again stores that 5 second amount of gas. This is
assuming that you're stopping to look and dial the machine each time it
go wacky and then the thing works for a bit again, but I'd say that
there's little in the machine and the supply of power that'll give what
sounds like the typical case of a lack of shield gas.

Does the machine have a real flowmeter (with a little tube and a ball in
it to indicate volume) or is it one that has a gauge to indicate flow?
If it's the gauge type you might find that there's an orifice on the
inlet, this could do exactly what you're describing.. as could foreign
matter in the regulator inlet

John

On Wed, 17 Sep 2003 04:41:58 GMT, "Keith Marshall"
wrote:

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?

I don't see how it could.

I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Not personally but I've certainly heard of them and was going to point you
to a site that repairs them at a reasonable price but their site is dead so
they may have gone out of business. It was http://www.welderboards.com in
case it's just a temporary problem with their site.

I just thought of something you might try to rule out a gas problem though.
Try a spool of fluxcore wire without the gas. Be sure you switch the
polarity first, usually by swapping the ground lead and the gun lead inside
the welder. That of course is assuming that the polarity *can* be switched
on that unit. If you still have the same problem it's definitely not a
problem with the gas solenoid, regulator, flow valve or tank.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"
"Alex Wiecek" wrote in message
. com...
Hello everyone...

First of all, I'd like to thank each and every one of you for taking
your time and advising me as to which direction to take to tackle this
problem.
In order to alleviate any confusion, I thought I'd come up with one
reply and address all your questions.... here it goes..

Zorro writes:

You may need to answer a few of the following to get more specific
help.

Is it mild steel or aluminum, you are welding?
We tried both.

Are you using solid wire, flux core?
Mmmm... I don't know.

Are you indoors or out in the wind?
Indoors.


Keith Marshall writes:
If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections.
If not
they can easily heat up and cause problems. Also, have you checked
that the
wire is feeding smoothly? If it's skipping or hanging up in the
liner it
can cause problems.

From what I could tell, the wire is feeding smoothly. He would know
better and I'm sure he'd see it first as he is a proffessional welder.

Also, if he's using gas make sure he has consistent flow.

This suggestion came up a few times. I'm trying to remember whether or
not he tried using a different tank. But I will check this next time
I'm in his shop.


Shipyard Worker writes:

Alex i had the same problem at work the voltage was fine then it
would
change five volts next time i put down the weld. It turn out to be
the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it
will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is
20
volts. I dont know if this helps. im dont work on welding machines
but i
do know what happen to me.

One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.


mylo writes:

Check voltage on contactor, line and load side!

The contactor is at the back of the unit? Or are you talking about the
power switch?
The contactor is just a power relay! follow the power cable in from the
back of the unit, the contactor should be located right after the
voltage selection terminal! At least all the machine i've worked on
had a contactor lincoln, linde, ltec and miller! How old is this
machine? I did'nt see it on www.lincolnelectric.com

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

I'm sure he would have noticed it. He is a very experienced welder.

check ground to work piece

Good idea.


IIt could also be a bad roll of wire!

We tried three different rolls....

if the wire is solid and not flux core it could be the gas solenoid!

This suggestion came up a few times... hmmmmm...
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Well.. apparently he used another welding machine on the same circuit
and it worked fine for him.

I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?
I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate
it.

Alex VE3GOP

It took me a few minutes to find the manual, but its on the lincoln
web site !!! I've have'nt looked at it yet , but if I come up with
something I'll past it on too!!!!!!!!!!!


On Wed, 17 Sep 2003 06:22:54 GMT, mylo wrote:

On Wed, 17 Sep 2003 04:41:58 GMT, "Keith Marshall"
wrote:

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?

I don't see how it could.

I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Not personally but I've certainly heard of them and was going to point you
to a site that repairs them at a reasonable price but their site is dead so
they may have gone out of business. It was http://www.welderboards.com in
case it's just a temporary problem with their site.

I just thought of something you might try to rule out a gas problem though.
Try a spool of fluxcore wire without the gas. Be sure you switch the
polarity first, usually by swapping the ground lead and the gun lead inside
the welder. That of course is assuming that the polarity *can* be switched
on that unit. If you still have the same problem it's definitely not a
problem with the gas solenoid, regulator, flow valve or tank.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"
"Alex Wiecek" wrote in message
.com...
Hello everyone...

First of all, I'd like to thank each and every one of you for taking
your time and advising me as to which direction to take to tackle this
problem.
In order to alleviate any confusion, I thought I'd come up with one
reply and address all your questions.... here it goes..

Zorro writes:

You may need to answer a few of the following to get more specific
help.

Is it mild steel or aluminum, you are welding?
We tried both.

Are you using solid wire, flux core?
Mmmm... I don't know.

Are you indoors or out in the wind?
Indoors.


Keith Marshall writes:
If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections.
If not
they can easily heat up and cause problems. Also, have you checked
that the
wire is feeding smoothly? If it's skipping or hanging up in the
liner it
can cause problems.

From what I could tell, the wire is feeding smoothly. He would know
better and I'm sure he'd see it first as he is a proffessional welder.

Also, if he's using gas make sure he has consistent flow.

This suggestion came up a few times. I'm trying to remember whether or
not he tried using a different tank. But I will check this next time
I'm in his shop.


Shipyard Worker writes:

Alex i had the same problem at work the voltage was fine then it
would
change five volts next time i put down the weld. It turn out to be
the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it
will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is
20
volts. I dont know if this helps. im dont work on welding machines
but i
do know what happen to me.

One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.


mylo writes:

Check voltage on contactor, line and load side!

The contactor is at the back of the unit? Or are you talking about the
power switch?
The contactor is just a power relay! follow the power cable in from the
back of the unit, the contactor should be located right after the
voltage selection terminal! At least all the machine i've worked on
had a contactor lincoln, linde, ltec and miller! How old is this
machine? I did'nt see it on www.lincolnelectric.com

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

I'm sure he would have noticed it. He is a very experienced welder.

check ground to work piece

Good idea.


IIt could also be a bad roll of wire!

We tried three different rolls....

if the wire is solid and not flux core it could be the gas solenoid!

This suggestion came up a few times... hmmmmm...
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Well.. apparently he used another welding machine on the same circuit
and it worked fine for him.

I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?
I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate
it.

Alex VE3GOP

On Wed, 17 Sep 2003 07:10:36 GMT, mylo wrote:

It took me a few minutes to find the manual, but its on the lincoln
web site !!! I've have'nt looked at it yet , but if I come up with
something I'll past it on too!!!!!!!!!!! I feel pritty stupid after looking at the schematic,
it don't have a contactor it uses scr's to switch power to the work as
you already indicated!! At any rate the schematic for the control
board is included in the manual!!


On Wed, 17 Sep 2003 06:22:54 GMT, mylo wrote:

On Wed, 17 Sep 2003 04:41:58 GMT, "Keith Marshall"
wrote:

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?

I don't see how it could.

I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Not personally but I've certainly heard of them and was going to point you
to a site that repairs them at a reasonable price but their site is dead so
they may have gone out of business. It was http://www.welderboards.com in
case it's just a temporary problem with their site.

I just thought of something you might try to rule out a gas problem though.
Try a spool of fluxcore wire without the gas. Be sure you switch the
polarity first, usually by swapping the ground lead and the gun lead inside
the welder. That of course is assuming that the polarity *can* be switched
on that unit. If you still have the same problem it's definitely not a
problem with the gas solenoid, regulator, flow valve or tank.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"
"Alex Wiecek" wrote in message
e.com...
Hello everyone...

First of all, I'd like to thank each and every one of you for taking
your time and advising me as to which direction to take to tackle this
problem.
In order to alleviate any confusion, I thought I'd come up with one
reply and address all your questions.... here it goes..

Zorro writes:

You may need to answer a few of the following to get more specific
help.

Is it mild steel or aluminum, you are welding?
We tried both.

Are you using solid wire, flux core?
Mmmm... I don't know.

Are you indoors or out in the wind?
Indoors.


Keith Marshall writes:
If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections.
If not
they can easily heat up and cause problems. Also, have you checked
that the
wire is feeding smoothly? If it's skipping or hanging up in the
liner it
can cause problems.

From what I could tell, the wire is feeding smoothly. He would know
better and I'm sure he'd see it first as he is a proffessional welder.

Also, if he's using gas make sure he has consistent flow.

This suggestion came up a few times. I'm trying to remember whether or
not he tried using a different tank. But I will check this next time
I'm in his shop.


Shipyard Worker writes:

Alex i had the same problem at work the voltage was fine then it
would
change five volts next time i put down the weld. It turn out to be
the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it
will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is
20
volts. I dont know if this helps. im dont work on welding machines
but i
do know what happen to me.

One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.


mylo writes:

Check voltage on contactor, line and load side!

The contactor is at the back of the unit? Or are you talking about the
power switch?
The contactor is just a power relay! follow the power cable in from the
back of the unit, the contactor should be located right after the
voltage selection terminal! At least all the machine i've worked on
had a contactor lincoln, linde, ltec and miller! How old is this
machine? I did'nt see it on www.lincolnelectric.com

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

I'm sure he would have noticed it. He is a very experienced welder.

check ground to work piece

Good idea.


IIt could also be a bad roll of wire!

We tried three different rolls....

if the wire is solid and not flux core it could be the gas solenoid!

This suggestion came up a few times... hmmmmm...
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Well.. apparently he used another welding machine on the same circuit
and it worked fine for him.

I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?
I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate
it.

Alex VE3GOP

I'm gonna guit while I'm behind! Iwas wrong again, there is no control
board schematic , just a wiring diagram, but i did notice a couple of
thermastats you might want to look at! Sorry I could'nt help more!!

On Wed, 17 Sep 2003 07:35:17 GMT, mylo wrote:

On Wed, 17 Sep 2003 07:10:36 GMT, mylo wrote:

It took me a few minutes to find the manual, but its on the lincoln
web site !!! I've have'nt looked at it yet , but if I come up with
something I'll past it on too!!!!!!!!!!! I feel pritty stupid after looking at the schematic,
it don't have a contactor it uses scr's to switch power to the work as
you already indicated!! At any rate the schematic for the control
board is included in the manual!!


On Wed, 17 Sep 2003 06:22:54 GMT, mylo wrote:

On Wed, 17 Sep 2003 04:41:58 GMT, "Keith Marshall"
wrote:

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?

I don't see how it could.

I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Not personally but I've certainly heard of them and was going to point you
to a site that repairs them at a reasonable price but their site is dead so
they may have gone out of business. It was http://www.welderboards.com in
case it's just a temporary problem with their site.

I just thought of something you might try to rule out a gas problem though.
Try a spool of fluxcore wire without the gas. Be sure you switch the
polarity first, usually by swapping the ground lead and the gun lead inside
the welder. That of course is assuming that the polarity *can* be switched
on that unit. If you still have the same problem it's definitely not a
problem with the gas solenoid, regulator, flow valve or tank.

Best Regards,
Keith Marshall


"I'm not grown up enough to be so old!"
"Alex Wiecek" wrote in message
le.com...
Hello everyone...

First of all, I'd like to thank each and every one of you for taking
your time and advising me as to which direction to take to tackle this
problem.
In order to alleviate any confusion, I thought I'd come up with one
reply and address all your questions.... here it goes..

Zorro writes:

You may need to answer a few of the following to get more specific
help.

Is it mild steel or aluminum, you are welding?
We tried both.

Are you using solid wire, flux core?
Mmmm... I don't know.

Are you indoors or out in the wind?
Indoors.


Keith Marshall writes:
If you haven't already checked,
make sure the gun and the ground cable have firm, clean connections.
If not
they can easily heat up and cause problems. Also, have you checked
that the
wire is feeding smoothly? If it's skipping or hanging up in the
liner it
can cause problems.

From what I could tell, the wire is feeding smoothly. He would know
better and I'm sure he'd see it first as he is a proffessional welder.

Also, if he's using gas make sure he has consistent flow.

This suggestion came up a few times. I'm trying to remember whether or
not he tried using a different tank. But I will check this next time
I'm in his shop.


Shipyard Worker writes:

Alex i had the same problem at work the voltage was fine then it
would
change five volts next time i put down the weld. It turn out to be
the
scr but how they describe it is one regulate the voltage in and one
regulate voltage out. but if the voltage going in is not right it
will
confuse the voltage going out. example: 32 volts in standered, but
actually it is 28 then the output should be 24 but in reality it is
20
volts. I dont know if this helps. im dont work on welding machines
but i
do know what happen to me.

One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.


mylo writes:

Check voltage on contactor, line and load side!

The contactor is at the back of the unit? Or are you talking about the
power switch?
The contactor is just a power relay! follow the power cable in from the
back of the unit, the contactor should be located right after the
voltage selection terminal! At least all the machine i've worked on
had a contactor lincoln, linde, ltec and miller! How old is this
machine? I did'nt see it on www.lincolnelectric.com

check wire feeder for proper wire tension! do this by removing the
ground from the work and make sure your wire pushes the gun from the
work piece!

I'm sure he would have noticed it. He is a very experienced welder.

check ground to work piece

Good idea.


IIt could also be a bad roll of wire!

We tried three different rolls....

if the wire is solid and not flux core it could be the gas solenoid!

This suggestion came up a few times... hmmmmm...
assume the machine is single phase, if it's a 3-phase machine you
might be losing 1 leg of the line!

Well.. apparently he used another welding machine on the same circuit
and it worked fine for him.

I have both welding and electronics background and
most of the machines i,ve worked on usually ends up to be your
consumables , tips, liners, wire, etc! And the user! The 2 major
component i've have to replace are contactors and diodes! You can
usually burnish the contacts inside the contactor!!

OK...let me ask you this: if there was a problem with the gas feed
to the gun, would this cause voltage variations and the control
board's inability to properly regulate the output voltage?
I checked the SCRs using a low power load, they worked fine but I
wonder if their behaviour would be different under load?
Have you ever seen control board failures?

Once again, thank you all very much for your help. I really appreciate
it.

Alex VE3GOP

On 16 Sep 2003 19:11:07 -0700, (Alex Wiecek) wrote:
One thing I should mention, and I forgot in my original posting, is
that I had my voltmeter sitting on the filter caps. The measured
voltage was about the same as the one on the dial. While he was
welding, the voltage held up pretty good until the weld started to
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.

It is very unlikely to be a microprocessor problem with those symptoms.

To me it indicates a high resistance developing as some poor connection
heats up in the circuitry feeding the filter capacitors. If you have an IR
temperature gun, look for hot spots when the welder malfunctions.
(If you don't have a noncontact temperature probe, unplug the welder
and *immediately* feel around for hot spots when it acts up.)

Likely places to look would be the bolted connections to the SCRs,
primary or secondary connections to the transformer, the circuit breaker,
etc.

I know you said you checked the filter capacitors, but they could still
be at fault. One or more of them could be developing a high ESR as
they heat up under full load. But I'm betting on a loose or corroded
bolted connection somewhere in the circuit before the capacitors.

Gary

The contactor is at the back of the unit? Or are you talking about the
power switch?
The contactor is just a power relay! follow the power cable in from the
back of the unit, the contactor should be located right after the
voltage selection terminal! At least all the machine i've worked on
had a contactor lincoln, linde, ltec and miller! How old is this
machine? I did'nt see it on www.lincolnelectric.com


Mylo... there is no relay. All I've seen is a knife type power switch.
I did consider cleaning that thing off at one point but if the switch
was dirty,
I would most likely have problems with the logic +5 volts on the
control
board. The +5v is solid as a rock...with no ripple.
The machine is about 13 years old, you can find the block diagram at
http://content.lincolnelectric.com/p...S/obsomenu.pdf.
Model number is WM-250

thanks
Alex

(doug) wrote in message . ..
On 15 Sep 2003 18:55:57 -0700, (Alex Wiecek)
wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld



sounds simple bit check the welding wire for rust or feed problems
doug

Hi Doug...

Being an experienced welder, I'm pretty sure he would have noticed
feed problems
but this sure is worth exploring. We tried three different spools of
wire with the same effect.

Alex

JohnM wrote in message ...
Alex Wiecek wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

This sounds to me like you've got either an obstruction in the regulator
or the tank valve isn't allowing adequate flow.. it sounds like the
shield gas is accumulating in the system but the reg. isn't supplying
enough volume, it's not keeping up with the demand. It recovers between
attempts to weld and again stores that 5 second amount of gas. This is
assuming that you're stopping to look and dial the machine each time it
go wacky and then the thing works for a bit again, but I'd say that
there's little in the machine and the supply of power that'll give what
sounds like the typical case of a lack of shield gas.

Does the machine have a real flowmeter (with a little tube and a ball in
it to indicate volume) or is it one that has a gauge to indicate flow?
If it's the gauge type you might find that there's an orifice on the
inlet, this could do exactly what you're describing.. as could foreign
matter in the regulator inlet

John

John...

if I recall correctly, the weld goes from good to wacky to good to
wacky in a rather predictable cycle. During all that, I've been
measuring the voltage accross the bank of capacitors and while the
weld was good, the voltage measured a steady DC voltage with small
amount of AC ripple on it.
As soon as the weld begun to screw up, the DC voltage varied all over
the map and the AC component was about 6 VAC. To me this indicates
poor regulation due to an overcurrent condition or the inability of
the control board to regulate the output voltage or even perhaps one
of the SCRs going wanky.
Both SCRs were bench tested good although I was only able to test them
at much lower current.
I wonder whether or not the problem with the gas supply might have
something to do with voltage regulation but I can't really see why it
would.
I don't know what sort of a flowmeter this machine has. I took a quick
peek at the user's manual at
http://content.lincolnelectric.com/p...S/obsomenu.pdf
but haven't seen anything there. I might have missed it.

Alex

On 15 Sep 2003 18:55:57 -0700, (Alex Wiecek)
wrote:

Hi all... thanks for reading this.
I'm wondering of someone has experienced this problem or perhaps has a
solution to it.
I'm not a welder in any way, so please excuse some of my decriptions
below. Since I specialize in electronics, my friend has approached me
to check his welding machine out as it has been doing weird things
lately.
He is using a Lincoln Wirematic 250 welding machine and what happens
is that it will lay a nice weld for about 5 or so seconds which will
be followed by sputtering, bubbly and a rather ugly weld, this would
be followed by a nice weld once again and so on so forth... The
sputtering can actually be heard by an untrained ear.
There are four filter capacitors that parallel the gun to the ground.
All of them check fine on my cap meter at 30,000 microfarads ( I did
check them separately). There are also two SCR's that are used to
control the output voltage. I checked them and they seem fine,
although those have been checked in a low current application - about
500 mA, since I had no access to a 150 A source to give them "the real
test".
All that's left is the transformers, chokes, clamping diode (checked
OK), a shunt resistor and a control board.
I don't have the schematics for the control board but was able to
follow a few traces to see where the control signals are going to and
where the current and voltage sampling enter the board for processing.
So far the board seems fine but I can't be 100% sure.

Can anyone help me with this? Am I being led down a garden path by
looking in the wrong place? Has anyone ever experienced such a
problem?

All your replies would be mostly appreciated.

Thank you.
Alex

Hello Alex,
I would like to suggest that you fault find this unit
as though it was a normal electronic power supply.

To do that you would connect up a load resistor
to the output terminals and monitor the current
flowing in the resistor with an ammeter and monitor
the DC Voltage across the resistor with an Oscilloscope.

Now you can take all the time you need without
worrying about wasting wire and gas as you would
have removed the wire and turned the gas off.

From your junk box you could probably find resistors
of a few ohms to test the unit with a light load of
a few amps. Then parallel your resistors to obtain
a load current of several amps.
If the intermittent or rhythmic problem does not show
up with low current then test with a higher current.

Finding a cheap high current load is going to be
a problem. Maybe you could scrounge a few
yards of thin stainless steel mig wire from somewhere
and wrap it tightly round a house brick. Use some
screw tight electrical connections to hold some thick
copper insulated cable to the stainless wire and
submerge the brick dummy load into a bucket of water.

Maybe you will need a few buckets with brick loads,
in series and then in parallel to experiment with
different heavy load currents.

With your load current flowing you now have plenty
of time to poke, prod, look for hot bad joints
and make measurements.

That would be my approach Alex,
Regards,
John Crighton
Sydney

Maybe you will need a few buckets with brick loads,
in series and then in parallel to experiment with
different heavy load currents.

I think you just need the bucket of water as a load resistor. Measure the
resistance pure and add salt or baking soda as needed to reduce resistance to
the desired experimental level. To get even "fancier", put screws into the
bucket sides below water level to use as electrodes! Replace them as needed.

On 17 Sep 2003 03:34:51 -0700, (Alex Wiecek)
wrote:



if I recall correctly, the weld goes from good to wacky to good to
wacky in a rather predictable cycle. During all that, I've been
measuring the voltage accross the bank of capacitors and while the
weld was good, the voltage measured a steady DC voltage with small
amount of AC ripple on it.
As soon as the weld begun to screw up, the DC voltage varied all over
the map and the AC component was about 6 VAC. To me this indicates
poor regulation due to an overcurrent condition or the inability of
the control board to regulate the output voltage or even perhaps one
of the SCRs going wanky.
Both SCRs were bench tested good although I was only able to test them
at much lower current.
I wonder whether or not the problem with the gas supply might have
something to do with voltage regulation but I can't really see why it
would.
I don't know what sort of a flowmeter this machine has. I took a quick
peek at the user's manual at
http://content.lincolnelectric.com/p...S/obsomenu.pdf
but haven't seen anything there. I might have missed it.


I'd think that if the weld goes wacky it would definitely affect the
voltage. During normal welding the wire is shorting to the puddle in a
high speed smooth manner. But when loosing shielding gas the weld
becomes much rougher with the wire shorting in a unpredictable manner.
The welder can only do so much trying to keep the voltage up. At some
point it has to drop.

Wayne Cook
Shamrock, TX

To me it indicates a high resistance developing as some poor connection
heats up in the circuitry feeding the filter capacitors. If you have an IR
temperature gun, look for hot spots when the welder malfunctions.
(If you don't have a noncontact temperature probe, unplug the welder
and *immediately* feel around for hot spots when it acts up.)


Good idea Gary. I'll keep that in mind.

Likely places to look would be the bolted connections to the SCRs,
primary or secondary connections to the transformer, the circuit breaker,
etc.


SCRs were taken off for testing. Transformer is a likely suspect.
Circuit breaker can probably be ruled out as he was using another
welding machine on the same circuit. Although the power switch of the
welding machine in question might have something to do with it.

I know you said you checked the filter capacitors, but they could still
be at fault. One or more of them could be developing a high ESR as
they heat up under full load. But I'm betting on a loose or corroded
bolted connection somewhere in the circuit before the capacitors.


The capacitor issue. I had the same feeling. I mean after 13 years of
high current operation and they still maintain their original
capacitance?
We might just change the caps as well as the SCRs on spec. Just
because...

But sure enough we will check all the connections...

Thanks Gary!

Alex

I wonder whether or not the problem with the gas supply might have
something to do with voltage regulation but I can't really see why it
would.
I don't know what sort of a flowmeter this machine has. I took a quick
peek at the user's manual at
http://content.lincolnelectric.com/p...S/obsomenu.pdf
but haven't seen anything there. I might have missed it.


I'd think that if the weld goes wacky it would definitely affect the
voltage. During normal welding the wire is shorting to the puddle in a
high speed smooth manner. But when loosing shielding gas the weld
becomes much rougher with the wire shorting in a unpredictable manner.
The welder can only do so much trying to keep the voltage up. At some
point it has to drop.


Hi Wayne...yes, this is a possibility that I will definitely explore.
I've seen many people mention the gas flow problem and maybe I'll get
lucky with this thing? I will try to meet up with him tomorrow to see
if I can spend some more time with his machine.

Thanks Wayne.

Hello Alex,
I would like to suggest that you fault find this unit
as though it was a normal electronic power supply.


Hi John...well, when you think about it, it really is a power supply.

To do that you would connect up a load resistor
to the output terminals and monitor the current
flowing in the resistor with an ammeter and monitor
the DC Voltage across the resistor with an Oscilloscope.

Now you can take all the time you need without
worrying about wasting wire and gas as you would
have removed the wire and turned the gas off.

From your junk box you could probably find resistors
of a few ohms to test the unit with a light load of
a few amps. Then parallel your resistors to obtain
a load current of several amps.
If the intermittent or rhythmic problem does not show
up with low current then test with a higher current.


Finding a cheap high current load is going to be
a problem. Maybe you could scrounge a few
yards of thin stainless steel mig wire from somewhere
and wrap it tightly round a house brick. Use some
screw tight electrical connections to hold some thick
copper insulated cable to the stainless wire and
submerge the brick dummy load into a bucket of water.

Maybe you will need a few buckets with brick loads,
in series and then in parallel to experiment with
different heavy load currents.

With your load current flowing you now have plenty
of time to poke, prod, look for hot bad joints
and make measurements.

That would be my approach Alex,
Regards,
John Crighton
Sydney

John, that's a fantastic idea. Problem is with resistors... I might
be able to scrounge a few here and there but I'm not sure how high
I'll be able to bring the amperage without smoking them.
I do have a 50 ohm/200 W load resistor for ham radio applications and
that should give me a few amps of load there.
But then again, I would probably want to go the other route (ie. brick and
a wire) as I really don't want to blow my dummy load.

But nevertheless, excellent idea there John. Thank you!

Alex

mylo wrote in message . ..
I'm gonna guit while I'm behind! Iwas wrong again, there is no control
board schematic , just a wiring diagram, but i did notice a couple of
thermastats you might want to look at! Sorry I could'nt help more!!


Hi Mylo... yes, that's the manual I was talking about. You got the
wiring
diag but no control board. I think that's a non repairable item but I
might be wrong. This thing is covered with a thick layer of conformal
coating.
I did check the thermostats but I'll check them again....short them
out if I have just to make sure all is ok.

thanks!
Alex

sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.

It is very unlikely to be a microprocessor problem with those symptoms.


Gary, one more thing...

The control board has quite a few feedback inputs. I was able to trace
a current sensing input as well as the output voltage one. There
might, or might not be a phase detector input as well which would
allow the micro to sync itself with the incoming AC phase and thus
fire the SCRs at a proper time.
I was kinda guessing that perhaps one of those inputs got messed up,
which would make the micro go awry and screw up the firing sequence.
Now that a few days have passed I question myself whether the
transition from good to bad and back to good weld was uniform and
predictable or random.

Alex

How about high intensity lamps for active/passive loads.

Not so much the screw in type, but they work - filament type not gas
type...

I was thinking SUN GUN or long strip glass tube with coil lamps.
Parking lots have them ..... Lighting store. - Electriction might have
some
junk/second hand holders - buy a couple of lamps - 1kw lamp goes a long
way.

Martin
--
Martin Eastburn, Barbara Eastburn
@ home at Lion's Lair with our computer
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder

On 17 Sep 2003 19:21:41 -0700, (Alex Wiecek) wrote:
sputter and burp. I've noticed DC voltage variations and quite an AC
ripple (about 6VAC). To me this indicates an excessive current flow or
the fact that the microprocessor is firing the SCRs at the wrong time
thus not regulating the output voltage properly.

It is very unlikely to be a microprocessor problem with those symptoms.


Gary, one more thing...

The control board has quite a few feedback inputs. I was able to trace
a current sensing input as well as the output voltage one. There
might, or might not be a phase detector input as well which would
allow the micro to sync itself with the incoming AC phase and thus
fire the SCRs at a proper time.

I was kinda guessing that perhaps one of those inputs got messed up,
which would make the micro go awry and screw up the firing sequence.
Now that a few days have passed I question myself whether the
transition from good to bad and back to good weld was uniform and
predictable or random.

My feeling is that such a desynchronization would very quickly result
in the SCRs being blown. In other words, the odds favor both legs
being active at the same time, which would present essentially a
dead short to the transformer secondary.

Gary

OK guys... the Wirematic saga continues. I haven't had time to look at
the machine for a few days and this might have helped things....
Today, I either had a brainstorm or a brainfart... and remembered
something that now I think I should have investigated further when I
took the SCRs out for testing.

When I removed the SCRs for bench testing, I've noticed that the
surface of both SCRs as well as the surface of the heatsink where the
SCRs make contact with, have either signs of pitting or corossion.
Where there was a bump in the heatsink, the corresponding point on the
surface of the SCR would have a dip.
At first, I didn't even think that this is pitting or corossion. My
initial thought was that this allows the SCR to sit tightly against
the surface of the heatsink and/or allows precise repositioning of the
SCR in case it is ever removed, etc.
Now, don't laugh as I have NEVER worked on high current equipment and
I really don't know what to expect when examining such problems.

Now that I'm thinking about it, it doesn't make any sense to me. You'd
expect to have a clean point of contact between the SCR and the
heatsink to allow the maximum transfer of current from the SCR to the
heatsink (and consequently to the gun). The uneven surface that I'm
seeing there is probably a result of moisture getting in there and
corroding the surface of both, or a sign on sparking.
It may not be as critical in low current equipment but I'd think that
it would make a heck of a difference in instances where a very high
current is needed at a steady voltage.

Can you guys confirm this for me? I am planning to go back to my
friend's either tomorrow or the day after.

Your thoughts would be muchly appreciated.

Alex