Miller Spotwelder WT-1530 control problem

Tue, 31 Aug 2021 10:13:57 GMT

go to see Welding Machine for Miller Spotwelder WT-1530 control problem

I have a three other portable miller spotwelders mostly given to me , fixed them all, just low voltage contact troubles.  The WT-1530 has an external timer box with some component vibrating crazily.  Any ideas as to which one it is?  Can't seem to isolate the sound.  I have the schematic from page 11 of the owners manual: OM-742A.  Downloadable from Miller.http://www.millerwelds.com/om/o742a_mil.pdfThanks,Alan
Reply:Are you talking about a soft buzz or a loud buzz?A soft buzz while welding is normal, a very loud buzz is not.If you can find and borrow an oscilloscope It can be used to check the operation of the SCRsCheck to see if they are firing equal in on time and amplitude.Get a clamp Amp meter and see what the current is in each SCR. I am going to guess that one SCR is either shorted or not firing at all.
Reply:Oh it's not normal!  It's a horrible racket from the whole box vibrating loudly.  It's not spotwelding, just making this sound.  While I do have a scope, it will be easier to try the amp clamp if I can get it around the cable.  As I recall my stick welder is making a similar noise but quieter presently, in the past  replacing the SCRs fixed the problem.  The contacts on my stick welders SCRs needed cleaning when I replaced them also, could that have contributed to their failure?Is there a surplus house that handles these large SCRs cheaper?Thanks,Alan
Reply:The big currant devices in there are diodes, I would have to break the case open to see what they are, not specified in this manual.  The thyristers and scrs are little things I could never get an amp clamp on, they are soldered on the board.  Could a miss-firing thyristor or scr could make the big diodes produce the sound?Thanks,Alan
Reply:The large devices are the SCRs. There are set up so, one fires on the positive half and the other fires on the negative half of the sign wave. This way they can turn on and off the AC primary voltage. Just put the clamp meter on the SCR lead to measure the current flow in each. A thyristor and  a SCR are two different names of the same device.Because of how they are wired, they can be used like a light dimmer to control the weld amps.A 150 amp stud diode and 150 amp SCR will look the same at first look. But the SCR will have small red and white wires. These are the gate control wires.Checked the service and parts manual. Q1 and Q2 are listed as diodes with bracket.Part number 106 634. These are the SRCs. See if there is a different 6 digit number on them.Miller has obsoleted this part number and the complete pc board part number.(038 437).New parts can be got from digi-key, newark, and ect. of you can have it repaired by one of the pc board repair places.
Reply:thanks, Ill hunt some down. Will post when working.Alan
Reply:Reread your post and yes it is possible that one large SCR is not being gated on.If one is on and the other is off. The spot welder will make a loud noise and even trip breakers.You can't measure the weld current, it is thousands of amps. you can look and the open circuit weld voltage and the SCR gate signals with the o-scope. If one is not firing you will see it in the weld voltage. Spot welders are AC. Around 3 VAC open circuit.The Large SCRs can be tested using a flash light bulb and batteries. Hooked up right you can turn the Light bulb on and off. Just unbolt them one at a time and test them on the table.If you want more detailed information I have a sheet that I can e-mail you. Just PM your address to me.
Reply:I have a portable miller WT-150 Pc board 038 437 with  problem  of SCR (Part number 106 634)Checked the service and parts manual. Q1 and Q2 are listed as diodes with bracket but i like know which is replacement (ECG =? ,   NTE =? , Voltage =? , Amp =?)6 digit number on them:  International Rectifier (IR) 022260 México 9129