POP! Burnback with MultiMaster 260 with nearly every start

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In 2001 I bought an ESAB MultiMaster 260, the finest welding machine I had ever laid hands on. It is the early version with the tan face. In MIG mode it had been really great, but it sets in my unheated barn shop so it is out of the rain and snow, but sure experiences environmental temp extremes. However about 2 years ago it began to have occasional problems with MIG mode. When I'd pull the trigger to begin a bead, It would create a loud "pop" sound as if a surge caused a hard burn back into the tip. I tried all sorts of adjustments and thought I was losing my welding ability (age, shaky hands, etc). I had good friends try to weld with it and we found a few minor problems, but the problem continued and became more frequent. Our welding supply shop suggested new wire, new liner, new contact tips, higher gas flow, etc. Intermittent problem continued and got more frequent. I took it into their repair shop, they installed another new liner and it worked well for the tech. I brought it home and the problem continued and got to the point where it is doing the hard burn back when first triggered 11 times out of 12 starts. So I have needed to use the stick welding mode for all needed welding since... and that mode works quite well (thankfully!). But I want this machine to MIG as it should.Specific machine details: Burn back dial used to be set at about 4, now at 0. Inductance module added and set about 1/4 rev from "0" position. No pulse module. Common wire first used .035 usually at 19-20 volts preset about 250-275 ipm. Now loaded with .025 17-18 V ~ 400 ipm. I went with the smaller wire to do some sheet metal repair in tractor fenders, but the .035 is my go-to for most everything else. I seldom weld new steel. Most of my work is repair on older equipment. I run 75/25 argon/CO2 mix gas. The electrical supply is single phase 240V 50A. It has never tripped the breaker.In reading other discussions on the WW forum, I see some discussion of failed SCR causing a surge, but they only related the surge to input power tripping the panel breaker. Do the SCRs come into play when in the stick mode? My stick mode seems to work well.Machine Serial number:  MORJ037137Thank You, Thank You! for any help you can suggest.     Paul in MN
Reply:I had a failed SCR in a Lincoln 250, that would start out good, then weld cold and pop like you described. It continued to get worse and had to replace the SCR.Do you have a run in setting on that machine? If so turn it off, make sure your wire is not slipping on the drive roll, or switch to knurled drive roll to test, have somebody watch the wire feed to make sure the drive is not stalling while welding, I have seen wire drive motors have issues and cause burnback or the motor drive board is going out.ESAB Rebels 215 and 235, ESAB HELIARC 281i, ESAB ET 301i, Hypertherm 85 and 45XP, Thermal Arc 185, TD 60i, HTP PRO PULSE 300
Reply:Since the Esab 260 is a chopper power supply, where are the SCR in it? It's a IGBT front end,and standard transformer machine.. (Super Switch is what Esab calls it) Never looked at a wiring diagram though..  I do know the 460 multi-power uses the same main board I also know a good running Esab 260/300 has a arc start that is rarely equaled.Last edited by Brand X; 10-10-2018 at 08:20 PM.Esab/Lorch ET-220iEsab 160i caddyThermal LM-200 Lincoln feedersThermal Pee-Wee 85sThermal 60i- 3phase /RPC powered (Beast)Thermal Drag-gun 35CINE 1500 Klutch 140i
Reply:Jaws...Thanks for your reply. In this case, once I get the weld started, it seems to run as long as I want to make that particular bead. Then it craps out as I start the next bead. I do not think there is any adjustment for run-in. A good friend who is an electrician and good hobby welder, and a very good mechanic has checked out the wire drive as I have triggered the torch. We did find some stickiness in the motion of the wire spool and solved that problem. We have run many tests with wire feeding by holding it back at the torch end, by turning down the preset voltage and then grabbing the wire between fingers to see if it would push, and now it does push with even speed and firmly without bird nesting. There was a problem with the spool sticking and the drive rolls slipping, but that is now solved. Unfortunately the "surge" burnback is occurring almost 100% of the time now. I will try the same tests again when this dog-gone rain stops, hopefully tomorrow.Thanks for your response!Paul in MN
Reply:Brand X,Thanks for your thoughts and response. I do have a copy of the schematic for this machine, but it is out in my barn shop. I do know the schematic shows SCRs and supposedly they are mounted on the big heat sink with the fan cooling them. I have visually checked out this area particularly looking for any possible mouse  or insect nests (thankfully none), and have blown out a small amount of barn dust. The fan works well. For the age of this machine, it seemed remarkably clean inside. Someone suggested checking the SCRs by removing them and checking them with an Ohm meter. I can do that, but I do not know what the acceptable values are, or if there are other tests to be done while they are out of the machine. I am suspecting that something has gone out on the main board which controls the SCRs. A good friend (described in above post) has a lab grade capacitor checking meter, and he isolated the 4 large capacitors, finding all within tolerance for their original specified capacitance as specified on the schematic (somewhere near 37,000 uf IIRC). My suspicion has now turned toward the main board. Are main boards available for this machine??I liked this MIG function so well that I convinced both of my sons to buy similar machines (a black face MM260, and a black face MM300). So we are deeply invested in the MultiMasters in our 3 shops. Those 2 machines are running excellently.Thanks for your thoughts and response.Paul in MN
Reply:Call Esab. Also get a # from the board, and see if these guys can help..https://www.innovatcorp.com/2018_pc_...air_price_listEsab/Lorch ET-220iEsab 160i caddyThermal LM-200 Lincoln feedersThermal Pee-Wee 85sThermal 60i- 3phase /RPC powered (Beast)Thermal Drag-gun 35CINE 1500 Klutch 140i
Reply:I hadn't thought about getting the number off the board, thinking that the machine serial # would be sufficient. But I will get the board # and then call ESAB tech support.Thanks for your encouragement.Paul in MN
Reply:Brand X,I hadn't read your post carefully enough at first to understand that the website citation you included is for a board repair company. I had no idea such a business existed. I have viewed their website and it looks like they work on many boards way beyond the welder industry. They look like a real treasure.Thank You!Paul in MN
Reply:Hi, I have a ESAB MultiMaster 260 which seems to have the same exact problem as yours.  Were you ever able to find a fix for yours?Rob
Reply:

Originally Posted by Rob1965

Hi, I have a ESAB MultiMaster 260 which seems to have the same exact problem as yours.  Were you ever able to find a fix for yours?Rob
Reply:The Esab 260 has one of the best arc starts on any machine ever made. The Migmaster 250 can be hit, and miss on arc start. Setup is everything, but some had issues no matter what. Although the Esab 250 Plus, and 275 really never had one issue there.Esab/Lorch ET-220iEsab 160i caddyThermal LM-200 Lincoln feedersThermal Pee-Wee 85sThermal 60i- 3phase /RPC powered (Beast)Thermal Drag-gun 35CINE 1500 Klutch 140i
Reply:

Originally Posted by Brand X

The Esab 260 has one of the best arc starts on any machine ever made. The Migmaster 250 can be hit, and miss on arc start. Setup is everything, but some had issues no matter what. Although the Esab 250 Plus, and 275 really never had one issue there.