Lincoln Idealarc Tig 300/300 - No Joy

[burnt_fingers]

So it seems after disassembly & testing, 3 inductors,1 trim pot & 3 transistors are bad on my board.
Lincoln support got back to me and the L5268T schematic is all they have even though it doesn't match this board exactly, its close.

Located the data sheet for the ge varistor I posted above, read through the information and the test results compare with the power specs, I think that part is ok.

Found 4 out of 5 transistors are open and 3 inductors have 0 inductance, Im sourcing out those parts to compare the new part readings to the old part.

The replacement AB current control rheostat got here, there's a seller on ebay right now $6 delivered.




Still need to ID and replace these 3 transistors, I checked 2 GE semiconductor manuals from 1971 & 1977 and they're not in there.
So far coming up empty on the search engines for the GED0 part numbers.
The T1006 cross references to NTE102A, but Id rather go with the same parts if possible.
In it to win it,
Doug

[burnt_fingers]

No progress identifying 3 of the five transistors I posted above.

Raines Iron gave me a big break and sent me photos of his L5269 board with those 3 transistors and the 2 SCR marked.
Solid Trevor! that really helped me out.



hunting down and ordering multiples of each part so I'll have spares on hand and the parts are just starting to trickle in.

I noticed the schematic doesn't match either of the 2 boards I have exactly, each revision Lincoln changed the control board.
It appears the only schematic they can provide is L5268, the boards are L5269, L5269B & L5271 so at least 3 revisions that I know of.

I'm going to put the newer board that doesn't match the schematic L5271 on the shelf for now and focus on the older board I have L5269B that at least matches the scheme for the most part and is almost exactly the same as Trevors.

The schematics are L5208T (welder) and L5268T (control board) grab them here: http://sdrv.ms/1ivBkKM

I'm still studying the schematic in an attempt to understand at least the basics.
which part is the actual power supply for the control circuit? where it enters & exits? what the control voltage should measure and from where?
The transformers are labeled H1, H2 & H3

H3- 76vac appears to be the primary welding current that powers the dc control coils.
H2 - 120 v powers the ac receptacle, fan and then leads to the diode/scr board and then directly to the control board, completes the circuit back to the diode/scr board.

H1 - ? Can anyone tell me what this H1 transformer circuit is for?




Also curious to know why some of the diode symbols in the control circuit (below) are circled and marked with 20v values?
Those diodes are circled in red, the 2 scr/pulse transformer circuits are circled in green.

I verified the diodes at those locations on the board, but they aren't any different than the other diodes that aren't circled?

[59halfstep]

Has there been any progress?

Charlie

[burnt_fingers]

Hi Charlie,
The short answer is no progress.
After all the dis-assembly,re-assembly and part replacements, still have the exact same problem, welds only on high with no control.

New parts for the control board arrived, transistors, inductors, resistors, put one of my control boards back together after isolating/checking every individual part, verifying the circuits and replacing parts I didn't believe were any good with exact replacements, cleaned up all the grounds and made sure the chassis parts are all bonded properly to each other & ground.
Got the new current control rheostat wired in on the panel and measured that circuit with the molex unplugged between pin #5 & #10 at the connector.
1-10 dial scale reads 10kΩ at 1 and lowers smoothly to 2Ω when you turn it up to 10.
Put it all back together and it's no different than before.

The machine will operate perfectly if I run a jumper from #10 at the panel remote switch to the ground side of the ac receptacle.
With the jumper on, she welds fine tig & stick, ac/dc in all the ranges with current control working both at the panel & the foot pedal.
High freq is working great as are the solenoids, soft start and switching between tig & stick - all seems to be right where it should be.

welded AC tig aluminum 120amps for a 2-3 hours continuously this week with the temporary jumper in place, nothing smoked or got warm, It did throw my 50 amp breaker during some long hot welds, but I reset it, gave it a few min break and went right back to welding and it didn't trip again.

I'm definitely open to suggestions, nothing I've done so far changed the original problem.
I'm tempted to send a board out, pay the $125 to "repair" wait a few weeks to get it and see if it makes a difference, but my gut feeling tells me it wont change.

Made a little progress on the machine in another way, bought a used procon pump and mounted it, the cart is the reservoir and will hold 40 gallons, right now I have 25 gallons of used red auto coolant in it and the pump is regulated to 50psi, I put serviceable fine mesh stainless screens on the input & output of the pump.
The few hours of welding I've done with it this week the torch is very cool to the touch and gets cold moments after you stop welding but its been cold outdoors and the coolant is probably 35-40 degrees right now, summertime temps will be a better test for that.

here's a few photos of the off topic cooler, I think its a Bernard cart?

[gnm109]

I would certainly make that jumper permanent and go with it. you say it works with the jumper? You win.

As to a 40 gallon water cooler....that's a little too much. I use 2.5 gallons in my Bernard and maybe 3 in my homemade water cooler. It has yet to overheat in the 15 years or so that I've used a cooler.

[burnt_fingers]

Beginning to work my way through and understand the circuits, It seems to me that grounding #10 is bypassing at least some or all of the control boards functionality, which indicates something on the control board must not be working.
The welder is not really needed and I can always jumper it to run it temporarily if I do need to use it, the jumper doesn't seem to destroy anything.
Fixing this correctly and hopefully pounding a little info between my ears is where I'm at right now.

[gnm109]

Beginning to work my way through and understand the circuits, It seems to me that grounding #10 is bypassing at least some or all of the control boards functionality, which indicates something on the control board must not be working.
The welder is not really needed and I can always jumper it to run it temporarily if I do need to use it, the jumper doesn't seem to destroy anything.
Fixing this correctly and hopefully pounding a little info between my ears is where I'm at right now.

I was a technical writer at Litton company for 10 years in the 1970's. They made running changes on their printed circuit cards quite often. They often used haywires (permament jumpers) on the backs of the boards to update existing items. Once they passed test, they were potted in and out they went to the customer.

Looks like you are doing a nice restoration. I was sorry that I sold my former Lincoln 250/250 Tig/Stick until I saw this thread and realized that parts are in short supply.

[AWPMAN]

Burnt Fingers,
My 300/300 is code # 7723 It has the L-5271 board.
The wiring diagram # is L-5764. I would get a copy and compair what you have.
Seems possible the wiring at remote switch may be crossed. This diagram shows it better. Mine is pinned out looking at the front of switch.
AWPman

[burnt_fingers]

Thanks for the info AWP, I'll get with Lincoln today, good possibility on the remote switch, it was modified by a previous owner instead of one DPDT switch they put in 2 SPDT switches side by side, the wiring as it is checks out exact with the schematic but I've been a little suspect of the arrangement.

[burnt_fingers]

Kevin @ Lincoln support replied: "I am attaching two prints. The L5764 that you requested but based on your code number 7723 I see the L5429 in the one you want"

Good thought AWPMAN, I compared the remote scheme and looks to be the same on all 4 prints, L5764, L5429 and the scheme for my machine L5208 & L5268.

Also seems to match the wiring that was done on my machine exactly, even though they used 2 separate spdt switches.
There is some additional info on both L5764 and L5429 that helps to explain the circuits better, they show an additional floating diode(and another diode) on the diode/scr board and that was driving me nuts because mine seems to follow this scheme from that print better than the one I have.

they also show line voltage compensation & control coil current sense to/from the control board, if I can match that up with mine will help to isolate some of the circuitry if nothing more than to at least help understand what's there and what it does.

I put all the prints here - L5208, L5268, L5764, L5429

[burnt_fingers]

Here’s a Recap so you don't have to go through all the previous info:

I got a Idealarc Tig300/300 code 7288 in not working condition and the previous owners couldn’t get it to weld either.
The welder was complete and didn't look like anyone hacked into it recently.
Took some time to dis-assemble it, small sections at a time and cleaned and traced out every connection and re-assembled.

Didn’t find anything bad except corrosion and general crustyness you would expect to find here in NY with a 40 year old machine that spent its life In a factory and then a while outdoors covered up.
by the end of the first day I got it to start up, fan runs fine, contactor locks right up, all the front panel switches checked out, HF is strong and good voltage at the stinger.
At this point wouldn’t weld unless it was on high and then there’s no current control just wide open.
After a few weeks I came across a replacement/rebuilt control board, verified with Lincoln support it would work with my machine because it’s a different part # and so I bought it. original board is L5269B and the replacement is L5271

Put the rebuilt board in, same issue: would not weld unless it was on high and then there’s no current control.

Decided one day to mess with the remote hand amptrol that came with the machine, it’s the original Lincoln unit on a 25ft tig torch and it looked ok. I plugged it in switched it to remote and it welded in all the ranges stick & tig but no fine control at the amptrol. Then I noticed the amphenol plug was loose and if I wiggled it would stop welding, took the connector apart and found all 5 wires bare, no insulation left and all were twisted together.

I fixed the amptrol connector, plugged it back in and then was back to where I started, wouldn’t weld unless it was on high and then there’s no current control.
That’s when I realized the amphenol connector was grounding #10 and that made it weld, tried a test jumper between #10 and ground on the ac receptacle and now I find she welds perfect, no smoke, nothing hot and welds in every range with good control.
Welded quite a bit this way over the past month, tig or stick, in all polarity and ranges and recently found a nice original pedal and that works great too as long as the jumper is on.

Next, I spent longer than I care to mention carefully dis-assembling both boards one at a time and isolating to check individual components, mapped out and marked the emitter, collector and base for all 5 transistors to correspond with the schematic, all five transistors were installed correctly and matched the scheme, found a few parts that seemed to not measure out well and I located exact replacements, resistors, capacitors, inductors and got all new transistors anyway even though they checked out, put both boards back together with new parts and double checked point to point with the schematic and here I am again.
Wont weld unless it is on high and then there’s no current control OR I can jumper #10 at the panel to ground on the ac receptacle and she welds seemingly perfect.
It acts like a bad control board, seems to me to indicate with the jumper on that I’m completing that circuit possibly losing some or all of the control boards functionality and that makes it weld.
But the fact that its acting the same with 2 separate control boards leads me to believe it might be something else. But what?

I verified the pilot relay is working properly, afterflow timer works perfectly, all the panel switches checked out good, replaced the front panel rheostat and that circuit checks out.

I know I can bite the bullet and send one of the boards out, wait 2 weeks, pay $125 and then find out and know for sure it was either the board or she’s still up to the same tricks. my gut feeling tells me its not the board.
There’s more value to me getting the repair experience including being able to rebuild the control boards than actually using the welder, I have other machines I can use.

If you have ideas, I'll try almost anything, by now its been a few months, I know every stitch of wiring inside/out and every component throughout the machine.

Doug

[irish fixit]

I assume you've checked the diodes on the diode and scr board. If not I would definitely start checking there. If the right ones where out then it might act the way your describing (if I'm reading the schematic right).

[burnt_fingers]

I did initially, a couple months ago now, took the diode/scr board out, setup a test circuit with 12v and a light following a Lincoln test procedure, scr's both checked out good gates latched and held, checked the diodes with only a multimeter on the diode setting and that leaves me wondering now., looking it over its still a little on the crusty side, It's isolated properly from the chassis.
I'll go back thru it and clean it up good, making sure the diodes are ok with current and verifying the wiring.

Been bothering me that I count all the diodes and have had 2 extra of the large diodes on that board, now that I have another schematic L5429 I got this morning, this scheme shows 3 diodes & the 2 scr , I think this follows my board better than what I was using and I'll make sure the diodes are working/wired right.

One more thing, its a little bit beyond my understanding at this point or even if its relevant but I've been using a calibrated tek digital storage scope to check voltages/waveforms and mostly to get a feel for the scope and see how useful that would be if at all for repairs like this.
I noticed without the jumper the output at #10 on the scope is a full wave dc rectification real clean signal and it doesn't weld, then when I put the jumper on the waveform changes to a half wave instantly also real clean and then the unit welds fine?.
I didn't take photos but this picture from the web illustrates the 2 waveforms I'm seeing with and without the jumper to ground.
The AC/DC waveforms at the stinger look clean & proper.

thanks for the help!! Doug

[burnt_fingers]

Took the diode/scr board out, disassembled to isolate each part and all the diodes test ok with no shorts or opens and current is flowing in the proper direction

thanks a lot AWPMAN for mentioning the L5429T schematic, my diode board had 2 floating diodes that wasn't shown on the L5268 schematic Lincoln sent me but matched that 5429 scheme perfect.

I would certainly make that jumper permanent and go with it.

Yep! throwing in the towel, made a sturdy permanent jumper between #10 on the remote switch and ground at the ac receptacle on the panel.
buttoned up all the sheet metal and stick welded a couple hours replacing bad areas of a frame on a dozer blade this afternoon.

machine runs like a swiss watch, nice smooth arc running 1/8" set on medium range with 30 foot of extension cord.
Ranks among the nicest stick welders I've ever used since my dad taught me to weld in the 1960's.

Not what I would normally call a proper repair or be satisfied with, but it works, nothings getting fried, it sounds and welds great in all modes.
that's going to have to do for now, I could have bough a new dynasty for all the hours put into this old girl
.
When it finally starts to warm up outdoors, I'll finish cleaning up the sheet metal and give it some new Lincoln gray and in the meantime going to use the hell out of it and see what happens.
thank you kindly for all the replies & troubleshooting help to everyone VERY much appreciated, Doug

[irish fixit]

I know you probably won't want to hear it but looking at it again there's another thing I see that could be checked. It's the 10k pot between wire 10 and 5 along with the switch on wire 5.

Since grounding it makes it work I started looking at the ground side. It looks like ground goes from the neg side of the rectifier through a 5k resistor, through another 1k resistor, possibly a diode (can't really tell on the schematic), a 5mh coil, to the remote switch (which this one needs to make contact when remote is disconnected), through the 10k pot, and then to wire 10.

That's the path I trace out on the 5268 schematic which is the only one with enough detail to trace all the way.

[AWPMAN]

Burnt fingers,
Ive had my 300/300 24 years. It went threw a hurricane in 89.Roof blew off building and it still worked.
I wondering if the 5 wires coming off of the diode board are correct. I see they list as 1234 but is this from the front of the board or back. 12 hour days so give me a few to get some photos and post.
AWPman

[ccawgc]

The jumper is shorting out one diode in the power supply bridge.
Post 40 may have a good thing to check.
PM me your e-mail I may have found something that will help you.

[burnt_fingers]

Right Wayne, I didn't want to hear it, but I'm over it now. HA!
I'm either going to need to see a shrink or a late night out to celebrate after this ordeal.



Trust me guys, Im a good listener and can translate all of your suggestions into action.
Whatever is causing the trouble, if its due to something on the pc board, its bad on both of the boards I have.
I couldn't find any other threads that dealt with this problem and was brought to a favorable resolution.


The wires going from the molex to the diode/scr board are printed on the wire jacket 1,2,3,4 and #1 is ground according to all the schematics, 2 & 3 go to the large scr gates and 4 joins the hot side of the 115ac between 2 diodes of the full wave rectifier.
and it does follow the scheme correctly when I trace out each one, so I believe they're in the right order, left to right 4,3,2,1


AWPMAN, if you get your cover off, I'd like to see a good photo of your L5271 control board for comparison.

What I think I know so far is the power supply is 115vac that goes into a full wave rectifier, the schematic leads you to believe the rectifier diodes are on the diode/scr board because of the dotted lines, but actually the 4 diode bridge is on the top left of the printed circuit control board.
I have 115ac coming in on #4 and coming out of the bridge circuit its 115dc where it continues into a pair of 47K 2w resistors there the voltage is reduced almost half with about 66dc volts going to the anodes of both small scr.
At this point I get fuzzy on what happens next, current sensing, switching and exactly how each of the 5 transistors applies to the scheme.

I'm going to re-visit and isolate the bypass capacitors and test each one on the bench with current, I think the 2 that are on the big power rectifier must be working fine if they were problematic I wouldn't be welding at all, there are 2 others that I've checked already but I'll double check them to be sure.

Great bunch of guys here, thanks for the help, Doug

[AWPMAN]

Burny Fingers,
Your picture in post 12 matches the wiring of my machine plug at the molex connector. The board is wired 4321 also matches. Keep posting seen some good replys and ideas.
AWPman

[irish fixit]

Ok. I've still not totally made sense of this circuit but I'm getting closer. However here's what you're bypassing with your wire.

The red line is your bypass connection. The other two lines are the circuit paths that you're bypassing. Which depends on the position of the soft start switch.


As you can see you're bypassing one of the diodes on the diode/scr board (and by going around that I think you're really going around two of them). There's also R16 trim pot on the control board, the second resistor left of Q1 (which is the soft start transistor).

I'm of the opinion that you've got at least two bad diodes on the diode/scr board. They may test good but be breaking down under voltage/load. It's the only thing that makes any real sense to me right now. It would explain why both control boards act the same way and why the bypass works (sort of).

[burnt_fingers]

I agree completely with how you mapped the jumper behavior, however the diodes that get bypassed with that jumper are not on the diode/scr board.
ccawgc called it a few posts back, those are power supply diodes that get bypassed.
The conclusion of the power supply diodes getting bypassed also match my scope readings where the waveform changes from fullwave dc without the jumper to halfwave dc measured at #10 when I add the jumper.
with that in mind and looking at the "jumper on" circuit map you created, it would seem to indicate something in area of the pc board outside the jumpered area to the right is bad and breaking the circuit.

I've checked the rectifier bridge diodes and I have 115ac into the bridge measured at #4 and #1 and 115dc out of the rectifier measured @ #23(+) and the 5k resistor(-)


What was confusing me is the schematic leads you to believe those power supply rectifier diodes are on the diode/scr board because its shown outside the dotted lines that designate the control board, It was a while into this before I realized that the 4 diode full wave rectifier bridge is on the top left of the printed circuit control board and also took a while for me to realize my diode/scr board doesn't match L5268.
I did a head count on all the diodes and although Im close now, it still doesn't add up with the schematics, so clearly they were in development and the schematics didn't keep up with the changes.
That also holds true with the 2 boards I have, the early board is L5269B, sort of follows the L5268 scheme pretty close, but the L5271 board does not follow it and Lincoln doesn't seem to have a revision for this updated board.

my diode/scr board matches L5429T I got from AWPMAN exactly.
there are 2 floating diodes and a third diode between the pos/neg leads to the control coils as well as the 2 large scr. this differs from L5268 where that scheme shows only one floating diode and the 2 large scr.
I feel pretty confidant the diode/scr board is working as designed.

[AWPMAN]

Burnt fingers,
Please post or pm the schematics in pdf for me. The link wont load.
AWPman

[burnt_fingers]

The schematics are L5208T for the welder code7288 and L5268T is for the L5269-B control board download here: http://sdrv.ms/1ivBkKM
Those files are too large to put here as attachments, some older browsers and mobile devices have trouble and may not load that Microsoft storage location, send a pm to me with your email and I'll send them to you directly.

I also uploaded the schematics to tinyupload, click the link and then when the page loads look for the pdf file name/download button:
welder L5208T

control board L5268T

[tommyjoking]

I sold on old 300/300 to a friend of mine years ago, he has never put it to use and I know he would sell it for $500 you pick up. The machine is in perfect working order except for the HF...needs a new cap soldered in behind the transformer. Just throwing that out there as I know it just collect dust in his shop.

[AWPMAN]

Pin 21 to 23 is closed shows resistor wire but its .4 ohm fluke meter. Let me review diagram will send more of what Id check.