Dialarc 250 AC/DC fried?

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Greetings,I purchased on old (mid-80s) Dialarc 250 AC/DC (no HF) stick welder about a year ago on bookface.  The machine worked just fine but I hate the plug type receptacles and wanted to convert it to Dinse-type in order to be able to use the a common set of leads between machines.  When I opened the box up, I noticed that the rheostat was in less than great shape and could see the play between the dial and the arm on the rheostat so I decided to replace that as well.  I could feel it giving a little bit previously when changing amperage but this was the first time that I'd seen it.  I found a replacement 15-Ohm 150-watt rheostat to replaced it and bought a new dial as well for good measure.  I changed out the plugs for new Dinse-type terminals and changed out the rheostat and dial and fired it up.  The machine fan started just fine, like it always has, but when I tried to start an arc to test it out, I heard a very quiet  and then the fan shut down.  There was also the slightest smell of ozone, but no flashes, no smoke, nothing else.  I checked the terminal cables and they weren't touching.  I know that I hooked the rheostat up correctly because I went directly from removing one wire from the old rheostat to replacing it on the new one.  Nothing was cross-wired, nothing else was done to the machine.My question is, based on this very admittedly limited information for a neophyte welder repairman, what are the chances that I've fried a board or something similarly expensive?  I didn't pay much for the welder and am really not interested in dropping hundreds of dollars in repair costs if it can even be repaired, but I would like to have it operational again.  Any idea how expensive it is to have somebody even look at an old dinosaur machine like this one?  I love the thing and am hoping that it can be fixed.  Something about the ungodly heavy transformer machines just appeals to me.Anyway, thanks for your time!Lincoln 305 LPGLincoln Power MIG 260Miller Dialarc AC/DCPrimeweld TIG 225Forney 180STLincoln WeldPak 100Primeweld Cut-50DP
Reply:Sorry mods--double tap.  Please delete.Lincoln 305 LPGLincoln Power MIG 260Miller Dialarc AC/DCPrimeweld TIG 225Forney 180STLincoln WeldPak 100Primeweld Cut-50DP
Reply:The Dialarc has no boards. It is a very simple design called a mag amp (magnetic amplifier). There are I believe 2 diode bridges in that machine, that is the only silicon that can fail. One diode bridge is low voltage low amps, to power the control circuit (the circuit the rheostat is in). And the other diode bridge is low voltage/high amps, to rectify the welding current from AC to DC. Other than those 4 diodes, there are 2 circuit breakers (one is for thermal protection) and a few ancillary resisters and capacitors for filtering purposes. Check the circuit breaker and thermal protection first. You could also remove and test the diodes. After that it is really about testing that the transformer is getting power and not shorted out.

Miller Multimatic 255
Reply:

Originally Posted by Louie1961

The Dialarc has no boards. It is a very simple design called a mag amp (magnetic amplifier). There are I believe 2 diode bridges in that machine, that is the only silicon that can fail. One diode bridge is low voltage low amps, to power the control circuit (the circuit the rheostat is in). And the other diode bridge is low voltage/high amps, to rectify the welding current from AC to DC. Other than those 4 diodes, there are 2 circuit breakers (one is for thermal protection) and a few ancillary resisters and capacitors for filtering purposes. Check the circuit breaker and thermal protection first. You could also remove and test the diodes. After that it is really about testing that the transformer is getting power and not shorted out.


Reply:In looking at the schematic, if the fan isn't operating the power switch may have failed or you blew a breaker in your main panel. The circuit breaker inside the machine shouldn't affect fan operation.Miller Multimatic 255
Reply:You are correct.  I blew the circuit breaker.  I realized it when I put the Dialarc to bed and plugged in my MIG welder to finish a job I was working on.  I'll plug it in again tomorrow and see if the fan at least starts up.  I still need to figure out where the short is.  One strange thing that I forgot to mention-when I pulled the old rheostat off, a large 1.5"x1.5" 3/4" chunk of metal fell from somewhere near the rheostat.  I didn't see where from because I wasn't looking inside the machine at the time because I was not expecting anything like that to be there.  The metal chunk has a hole drilled in the middle of it.  I am guessing that it was maybe used as a spacer though I don't know why it would have needed one.  The new rheostat is the same size and didn't need one.  Is it possible that this might have been used as a ground?Thank you for all of the help.  It is much appreciated!Lincoln 305 LPGLincoln Power MIG 260Miller Dialarc AC/DCPrimeweld TIG 225Forney 180STLincoln WeldPak 100Primeweld Cut-50DP
Reply:Maybe not a ground as much as a spacer would be my guess, since no ground connection is indicated on the schematic. But 12V71 is right. Make sure you didn't accidentally ground out one of the welding leads when you installed the DINSE connectors. That happens a LOT to folks. Something shorted out your machine causing the breaker to trip. Could be that chunk of metal you dropped in there if you didn't pull it out, could be the DINSE connector or it could be a bad diode. I would chase them in that order. When checking your DINSE connectors, if you have a welding lead that has continuity to the case (test with an ohm meter) that will be one of your problems.Miller Multimatic 255
Reply:Roger.  Thanks for the tips.  It will likely be the weekend before I have time to dig back into this thing.  I appreciate the suggestions though.Lincoln 305 LPGLincoln Power MIG 260Miller Dialarc AC/DCPrimeweld TIG 225Forney 180STLincoln WeldPak 100Primeweld Cut-50DP