Lincoln Idealarc Tig 300/300 - No Joy

[burnt_fingers]

I picked up this Lincoln Idealarc Tig300/300 a few months ago, no idea when it was working last but the last owner told me it does not work.
Lincoln Idealarc Tig300/300
CODE: 7288
SERIAL: AC-343342
It has the hand amptrol- no pedal
It's labeled single phase and I wired up a 220 plug and switched the input power from 460 down to 230 and have spent the past 2 months cleaning up the connections, tracing out each wire with the schematic and in between trying to get it to weld.
It starts up nice and smooth, fan runs fine, contactor locks up quick, I have 117vac at each leg.
I'm using the same outlet my other 220v welders run fine on and can rule out input power.

With the welder running I have 120v ac at the panel outlet, 70 vdc at the stinger in all the current ranges, polarity changes as expected with the polarity switch.
Can only weld on max with no current control.
I couldn't find any bad components on the L-5269B circuit board but to completely rule it out I picked up a refurbished L-5271 board. checked with Lincoln support and verified this replacement was suitable for the code 7288 machine, it looks almost identical to the original board except for 2 buss fuses which the old board doesn't have.
I checked the big diodes and the scr board and didn't find anything out of place.

Made no difference running with the new board, I cant get an arc in anything other than max with no current control.

Yesterday, I plugged the hand amptrol in, left the panel switch on the stick setting, and no matter if was set to remote or panel it welds now in all ranges but with no current control either by the panel or the hand amptrol.
Seemed like I was getting somewhere because it really stick welded great other than not having the fine control to dial it in, I was able to make some nice welds with various rods in both AC & DC.
Next I checked the T10812-34 current control pot on the panel, in circuit 0-5k ohms- out of circuit 0-13k.

Afterwards I took the hand amptrol apart and found all 5 wires in the 5 pin amphenol connector were twisted up all shorted together with no insulation.
I cut the cable back and wired it per the schematic, the micro switch is working fine, the T10812-60 current control pot reading 0-45k out of circuit.

Now that the hand amptrol wiring is not shorted, I plug it back into the panel and now when I run it Im back to it only welds on max with no current control.
Somehow the short, (assuming it was to ground) made it weld in all the ranges with no control?

Pilot relay is clean, wired correctly to the schematic and seems to be working fine when you switch ranges and also when I strike an arc you can see/hear the relay engage distinctly.
The panel/remote switch checks out with a meter as did all the other front panel switches.
Im at a loss as to how to proceed?
I can read a meter, methodically follow directions and will start right from scratch again if you have the time and knowledge to help me dope this out.
Doug


Photos/docs for the welder can be seen here: http://sdrv.ms/1hWHq1Q
The schematics are L5208T and L5268T grab them here: http://sdrv.ms/1ivBkKM

[burnt_fingers]

Checked the 2 bypass condensers up front and the 2 stacked in front of the power rectifier, values all closely match the L5268T schematic and all 4 have good grounds.

[burnt_fingers]

Put the old control board back in to do some experimenting this morning.
Welder started up and actually ran perfect for a little while, burned a few small rods in the lower ranges, the current control pot on the panel was working fine then lost the arc and back to square 1.
jumped #10 at the remote switch to ground and all ranges have the expected current and welds great but no current control.
tried to edit my previous post, don't know how to do this.
Doug

[burnt_fingers]

I don't have the privileges to edit my previous posts.

I found if I jumper #10 to ground where it connects with the panel current control pot at the remote switch(red arrow) - everything works.
Cant figure out why, but ran it quite a bit this way today and everything works, afterflow timer, solenoids, current control, remote amptrol.
tried different dia rods in all the ranges makes beautiful welds this way, nothing overheating, and no damage found on the control board(s) and the welder seems to be working perfect.
Any reason not to leave the jumper on and run it this way?
Doug


L5268.T control circuit

[ccawgc]

You have a open wire between the plug on the pcb and the rheostat on the front panel.
That is what you are jumpering. With the panel switch in local you should be able to test the rheostat at the pcb plug. See your diagram for pin numbers. You will have to chase the wire and find the break or bad connection point.

[burnt_fingers]

Hello ccawgc, thanks for helping me.
The front panel current control rheostat wires are #10 & #5.
With the extra jumper I added removed, switch in the panel position, remote amptrol unplugged and the plug to the pcb unplugged, checking resistance between #10 & #5 at the plug,
rheostat at 0 reads 13kΩ and as the pot is turned up to 10, I get a smooth change down to 1.2Ω - pretty much what I measured with the pot out of circuit.
I did the wiggle test on the plug & wiring and couldn’t get any variations on the readings.

the temporary jumper I experimented with connects #10 where it junctions at the remote toggle switch to the ground side of the AC receptacle which is common with the 120v xformer, scr/diode board, the fan & the pilot light and the chassis common at the pcb.
I checked resistance from there to other (grounded) locations of the chassis assuming something's not bonded and its all proper with no resistance.

[irish fixit]

It's possible you're getting a good reading with a meter but it's failing under load. It's fairly common for a bad connection or switch to read good with a meter but be pulled down under load. I ran into that the other day on a circuit breaker. It tested good till we actuated the control. Then it fell from 12v to 4v. Sometimes you've just got to check voltages instead of resistance.

[burnt_fingers]

Good point Wayne, thanks for the help.
I wired the circuit from the pcb plug to the remote/panel switch with a good strong 12vdc equipment battery into a utility light that should put a draw on it, just a quick flicker then nothing. worked the pot and couldn't get it to light up.
light is nice and bright at the panel switch running the juice through the harness from the pcb plug without the rheostat in line.
I'll have to get a new rheostat, the original is marked Allen Bradley T10812-34 and if Im reading the schematic right it shows 10k- when I get a new one, I'll be back with some news!
thanks fellas.
Doug

[irish fixit]

Glad you found it. Sometimes these type of faults can drive you nuts finding them.

[burnt_fingers]

I swapped in a big ohmite ceramic rheostat I had and setup the test circuit again from the plug at the pcb to the remote switch on the panel with 12v and a light, it lit right up with brightness adjusting as expected with the pot.
connected all back up to run and naturally you know what happened next.
NOTHING, she powers up fine, welds on max only with no control and nothing but a trickle in the other ranges.
Again, if I connect my experimental jumper from #10 at the remote switch to ground on the ac receptacle it welds in all the ranges and all seems to run fine.
Guess this leads me back to the pc board.

I have 2 boards, I couldn't find anything burnt or obviously bad on either one and I'd like to get the diagnostic experience and troubleshoot the boards myself, instead of sending it out, plus it's seems that most of time, I read the board comes back repaired, guy puts it back together, machine welds for 10 nano seconds and then its back to the same old story again.

In over my head now but I do know there are a bunch of smart guys here that I'm hoping will jump in to offer guidance to keep me on the right track.
I have a Tektronix 2232 scope I'm getting familiar with, a good waveform generator, dc power supply, various meters.

I'm open to and hoping for suggestions on how to proceed tracing out the newer L5271 board.
There are signs of previous damage, where a resistor blew and was replaced before I received it.



L5268T is not the exact proper schematic, but its very close minus the fuses.
grab a high res .pdf here: L5268T.pdf


I circled in red where I have 80+ volts dc at #23 from the diode/scr board- Is that the voltage in to the pcb that powers the current control?

Diode/SCR board outlined in green
PC board outlined in blue
#10 & #5 at the front panel/remote switch- 10k current control rheostat in yellow.


I have to trace out the pin-out of the 15 pin molex connector, then unless someone has a better plan, I'll try to divide & conquer.
starting where #23 enters the board, put some voltage to that pin at the connector and then try to follow it, split the board into sections I can test and verify to see if I can find the bad component(s).
Doug

[burnt_fingers]

I'm checking with Lincoln support to see if there may be another schematic for the updated board.

My first question on the schematic is the arrow symbols, they look like sideways chevron with 2 stripes.
Stripes with a number? this corresponds to each harness wire respectively? 2,5,10,21,22,23,24 &25 - And what do the arrows signify?

Thanks Doug

[burnt_fingers]

A few reference photos of the L5271 control board.
pin 1 the trace is gone and they jumped it with solid wire.

[irish fixit]

I'm checking with Lincoln support to see if there may be another schematic for the updated board.

My first question on the schematic is the arrow symbols, they look like sideways chevron with 2 stripes.
Stripes with a number? this corresponds to each harness wire respectively? 2,5,10,21,22,23,24 &25 - And what do the arrows signify?

Thanks Doug

The double arrows represent a plug. In this case the molex plug on the board.

Your high resolution pdf of the schematics is pretty close to unreadable on my end.

[burnt_fingers]

That's all Lincoln gave me, this was for the original pcb, they said will get back to me if they find there was an updated version for the L5271.
opened with adobe reader you should be able to zoom in adequately.
Ok on the plug symbol, Thanks!
that means 8 out of the 13 connections are already marked.**edit Located the rest of the "chevron" plug symbols- thanks Wayne

most of the components on the board I can identify so far but this item below, there are a pair of these above the fuses, I don't know what they are:
both identical, im looking on the schematic tonight to match up the symbols with this pair.
The terminals seem to be marked K A G

[gnm109]

I think that the items marked "K A G" are the two SCR's for the board. Anyway, they look like SCR's that I've used on my model railroad to control currents in various modules that I use. I have a couple of old Troller power packs that supply 0-12 VDC and there is an SCR in each one, along with a rectifier to provide the DC. Just a guess. Hope it helps.

I used to own a Lincoln Idealarc 250/250 TIG/Stick and I'm sorry I sold it. They are a great unit when running properly. Hope you get it fixed!


EDIT: Those are definitely SCR's.

http://www.weldingmart.com/lincoln-e...s-scr-s15161-6

[irish fixit]

Those are scr's. They're on the left side of your diagram.

[irish fixit]

I think that the items marked "K A G" are the two SCR's for the board. Anyway, they look like SCR's that I've used on my model railroad to control currents in various modules that I use. I have a couple of old Troller power packs that supply 0-12 VDC and there is an SCR in each one, along with a rectifier to provide the DC. Just a guess. Hope it helps.

I used to own a Lincoln Idealarc 250/250 TIG/Stick and I'm sorry I sold it. They are a great unit when running properly. Hope you get it fixed!


EDIT: Those are definitely SCR's.

http://www.weldingmart.com/lincoln-e...s-scr-s15161-6

Yeah but there LOTS cheaper places to buy them. Never buy stuff like that from a welding supply. Go to a electronics supplier of some form. Heck even Amazon has that beat by a mile.

http://www.amazon.com/NTE-5556-600V-.../dp/B0002FRLVY

[irish fixit]

Here's a pretty good circuit symbols page. It at least allows you to click and get a explanation of what the device is. It doesn't have all the symbols unfortunately.

http://www.rapidtables.com/electric/...al_symbols.htm

Here's another.

http://en.wikipedia.org/wiki/Electronic_symbol

[irish fixit]

Ok. I'm having a hard time following all the logic on that board. I can't see how jumpering pin 10 to ground isn't just burning up the board actually. That should be the hot side from what I can make out.

One question. Have you found any info on adjusting the two trim pots on the board?

They are hooked into the circuit near pin 10 and would be prime suspects to me. You might make note of there starting position and try moving them back and forth a couple of times to clean there connection putting them back where you found them.

You might also check continuity on the little choke coil attached directly to pin 10 and the two trim pots. It might be burned out.

At least that's where I would start. It's hard for me to follow all of this without the machine right in front of me and my electronics knowledge is just enough to get me in trouble. I'm pretty good at repairing but not so good on theory.

[irish fixit]

Ok. Done some more looking. Looks to me like ground goes into the board via wire 1 at pin 6. I can't find that pin in the control board schematic as of yet but you might check on how good a connection that wire is making to the board.

[irish fixit]

I'm starting to get some of this untangled now.

First off I'm fairly certain that wire 10 should be the positive side of the control circuit.
Have you tried the soft start switch? If you have then you might want to check and make sure it's making good contact and sending power into the circuit board when on.

[gnm109]

Yeah but there LOTS cheaper places to buy them. Never buy stuff like that from a welding supply. Go to a electronics supplier of some form. Heck even Amazon has that beat by a mile.

http://www.amazon.com/NTE-5556-600V-.../dp/B0002FRLVY

I made no recommendation where to buy them or if he should buy them. When I worked more with electronics, they were very cheap. Radio Shack still sells them. The issue would be finding SCR's that are the same electrically as the named part number. If a change is made to a different, allegedly equivalent part number, the entire board might have to be readjusted (read resistors, capacitors). That would be devilishly hard without a test procedure.

[burnt_fingers]

Very much appreciated fellas!

Ok. Done some more looking. Looks to me like ground goes into the board via wire 1 at pin 6. I can't find that pin in the control board schematic as of yet but you might check on how good a connection that wire is making to the board.

The #1 ground is bonded at the chassis right below the diode/scr board- 1-4 runs from the terminal strip on the diode/scr board to the molex, the rest of the wiring comes in thru the main harness to the molex.



I agree there should have been fireworks when I grounded #10 - at the point now where I'll not do that again. don't want to continue creating my own problems.

I'll keep looking for the bad parts on the 2 boards I have, it doesn't matter to me right away if it welds or not I have other machines to weld with.
In between troubleshooting I'll keep cleaning up the sheet metal so I can paint it when it warms up.

the 2 chokes at #10 & #5 test out good for continuity, I read up about a small circuit I can build with a 100Ω resistor and then with my waveform generator & scope using voltage drop/frequency readings there's a formula to measure the choke capacity but I haven't tried it yet.

buying parts at a welding supply would be like buying small block chevy parts at the marina for your boat, not good for the wallet but they usually did the research for you and you get the right stuff, sometimes its worth a little more but you can always do the leg work yourself.
I always kill myself to try and get exact replacements, but sometimes 40 years later its completely impossible or you're just putting back in 40 year old parts that may not be as good as a modern replacement and not likely this circuit is going to be fussy about precise values as long as its close to the original design.

I'll check the small trim pots, the schematic shows 50k and 10k ? hard to read, but the part numbers look to me like 20k & 5K?
excellent point to start with, possibly the wiper in those pots are acting just like the current control pot was on the panel, seems fine with the meter but no good with current. - thank you kindly- Doug

[burnt_fingers]

All the caps, transistors, trim pots & the pulse transformer off completely and test out good, except the transistors they're off but I haven't checked each one yet, most everything else lifted out of circuit tests good so far.
testing each item under power with a signal gen, scope & bench supply @40vdc
Found one resistor that someone replaced where the board was previously burnt, was the wrong value for that location. should have been 10 ohm and they used a 460ohm instead.
5K trim pot is pretty close, 20K has a problem, they both adjust smoothly going up/down, one half of the 20k is reading too low.

Located an Active SCR test procedure for the Lincoln DC1000.
I used it to test the larger SCR's on the diode/scr board a few weeks ago, its straightforward and easy to follow,
.xps file wouldn't allow me to attach, grab it here - Active SCR Test.xps

no smoking gun yet - Doug

[burnt_fingers]

Started putting the board back together, most everything including the 2 SCR tests out good.

this part below however had nothing written on it to identify, on my other board in the same position its labeled V150LA10A
searches up as a varistor.
I read various descriptions and tests, most mentioned putting voltage through it and then reading what passes through.
the data sheet I read for the V150LA10A listed 200vdc max so that's what I went up to.
Tested with my Jackson 112 condenser tester as the power supply it will put out up to 500vdc.

I didn't get the sense from what I read, that the voltage passed was supposed to be reduced, but that's whats happening.
45vdc in = .32vdc out
93vdc in = 2.3vdc out
196vdc in =19.4vdc out

Is the varistor working properly or just add this part to my shopping list for new parts and replace it or other tests?

Back to work! - Doug