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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: 7288SERIAL: AC-343342It has the hand amptrol- no pedalIt'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.DougPhotos/docs for the welder can be seen here: http://sdrv.ms/1hWHq1QThe schematics are L5208T and L5268T grab them here: http://sdrv.ms/1ivBkKM
Reply: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.
Reply: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
Reply: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?DougL5268.T control circuit
Reply: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.
Reply: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.
Reply: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.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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
Reply:Glad you found it. Sometimes these type of faults can drive you nuts finding them.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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.pdfI 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 greenPC 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
Reply: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
Reply:A few reference photos of the L5271 control board.pin 1 the trace is gone and they jumped it with solid wire.
Reply:
Originally Posted by 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
Reply: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 Waynemost 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
Last edited by burnt_fingers; 01-29-2014 at 09:58 PM.Reason: symbols are helpful to know
Reply: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-s15161-6Last edited by gnm109; 01-29-2014 at 10:23 PM.Miller Millermatic 252Miller Syncrowave 200Liincoln AC-DC 225Victor O-A Set
Reply:Those are scr's. They're on the left side of your diagram.
Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:
Originally Posted by 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
Reply: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.htmHere's another. http://en.wikipedia.org/wiki/Electronic_symbolMillermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply:
Originally Posted by irish fixit
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
Reply:Very much appreciated fellas!
Originally Posted by 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.
Reply: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 @40vdcFound 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.xpsno smoking gun yet - Doug
Reply: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 V150LA10Asearches 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 out93vdc in = 2.3vdc out196vdc in =19.4vdc outIs 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
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
Reply: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/1ivBkKMI'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 & H3H3- 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?
Reply:Has there been any progress?CharlieCharlie
Reply: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?
Reply: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.Miller Millermatic 252Miller Syncrowave 200Liincoln AC-DC 225Victor O-A Set
Reply: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.
Reply:
Originally Posted by 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.
Reply: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
Reply: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.
Reply: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
Reply:Heres 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 couldnt 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.Didnt 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 wouldnt weld unless it was on high and then theres 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 its a different part # and so I bought it. original board is L5269B and the replacement is L5271Put the rebuilt board in, same issue: would not weld unless it was on high and then theres no current control.Decided one day to mess with the remote hand amptrol that came with the machine, its 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, wouldnt weld unless it was on high and then theres no current control.Thats 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 theres 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 Im 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 shes still up to the same tricks. my gut feeling tells me its not the board.Theres 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
Reply: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).Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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
Reply: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 directionthanks 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.
Originally Posted by gnm109
I would certainly make that jumper permanent and go with it.
Reply: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.Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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. AWPmanLast edited by AWPMAN; 02-18-2014 at 09:45 PM.
Reply: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.
Reply: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
Reply: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
Reply: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).Millermatic 252XMT 304'sDynasty 280DXHypertherm PowerMax 1250Miller Trailblazer 302 EFIOptima PulserXR feeder and XR Edge gun and more athttp://members.dslextreme.com/users/waynecook/index.htm
Reply: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.
Reply:Burnt fingers, Please post or pm the schematics in pdf for me. The link wont load.AWPman
Reply:The schematics are L5208T for the welder code7288 and L5268T is for the L5269-B control board download here: http://sdrv.ms/1ivBkKMThose 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 L5208Tcontrol board L5268T
Reply: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.
Reply: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.Last edited by AWPMAN; 02-21-2014 at 07:19 PM. |
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发表于 2021-9-1 23:16:23