Shopmaster 300 troubleshooting
RSS | Subscribe | Contact Us | Advertise | About Us
Results 1 to 17 of 17
  1. #1
    Join Date
    Feb 2012
    Posts
    10

    Shopmaster 300 troubleshooting

    Hey guys, looking for some help with my Shopmaster. It's a 1994 model I bought used. Machine was working fine, now it just blows the breaker on startup. I flip the switch and the breaker instantly trips, fan doesn't even spin up. Any ideas where to start? It does this regardless of which process I select.

    Any help would be greatly appreciated! My local miller place says it's "probably a capacitor" but looking at the electrical circuit that makes no sense since the only caps are on the welder output side and it's tripping prior to striking an arc

    Thanks!!

  2. #2
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    2,525

    Re: Shopmaster 300 troubleshooting

    the cap bank is only used in mig, so if it trips in stick the caps are not the cause.
    But inspect the top of all the caps. look for burnt screw heads and holes in the vent plugs.
    Cap banks do fail this way with age.
    But on your welder we need to check the weld SCR/ diodes. see if any are shorted.
    By disconnecting a few wires we can make sure the transformer and the diode/ SCRs are all good. One more ware point to check is the mode switch blades. Make sure they are bot burnt to the point where they no longer make connection. When these welders are used in only one mode all the time, they have a bad habit of burning open. Just one contact set in the middle of the switch.

  3. #3
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Thanks for your reply! I will check the above and report back. I hope to tear into it tonight.

    Looking at the circuit, I can troubleshoot the SCR pucks with a continuity/diode test correct?

  4. #4
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Other than this(top one):



    The entire cap bank tests fine. Even the defective screw head didn't make it inop. Looks like it just loosened up.

    SCR pucks also test good, connected meter to anode/cathode on the connector that hooks to PC1....Found a resistor that got a little warm on PC1. Still reads 1Kish ohm but I don't know if they are in series/parallel with other resistors I'm going to desolder it and see if it tests out.



    Also checked mode switch blades - none are burnt and have automotive type grease on the blades. I checked continuity across the blades they engage with in each mode and they were OK
    Last edited by ELake; 02-22-2012 at 07:32 PM. Reason: Added PC1 picture and mode switch info

  5. #5
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Stupid question.....

    You use the jumper links that match your machines front panel voltage range correct?

    I brought the thing home from the shop a couple months ago and just recently went to use it again (I work out of town for months on end) I must have been about 12 beers deep when I decided to relink from 460 to 230 - my machine is 200/230/460 and I had the 2 links on the bottom 4 terminals......Rooting around I see that L2 is fed from wire #17 which is 5 posts from the bottom so this wasn't linked with the transformer and the manual says for my front panel voltage that they need to be linked (from bottom up) 2&3 and 4&5 I feel like an idiot.

    Going to get a replacement resistor tomorrow, was able to salvage the cap by retapping (m5x.8) and filing down the carbon. Resistor tests good off of PC1 but the color codes are burnt off of it and it's probably on borrowed time anyway

    While I've got it apart any other tests I could perform would be great but I'm thinking it's a simple input jumper problem.

  6. #6
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,575

    Re: Shopmaster 300 troubleshooting

    Correct on the jumper link question. One could say you "jumped" the gun but hopefully you dodged the bullet.

    Good save on the caps and as for any further testing you said the SRCs tested good so I'd suggest a second or third look see to verify nothing else is questionable after replacing the resistor - prior to anymore - plug it in and pull the trigger (turn the machine on).

    If that's resistor R98, it should be a .25W, 4.7K.

    Correction: R99 = .25W, 1K ohm.
    Last edited by duaneb55; 02-23-2012 at 12:22 AM. Reason: added resistor info
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    SA-200 Blackface Code# 8638
    Star Jet 21-110

    Two term limit - one in office, one in jail.

  7. #7
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Cool thanks

    Resistor in question is R90, appears to be a 1k 1/4 watt. How critical is accuracy? Was going to replace with one from radio shack.

  8. #8
    Join Date
    Mar 2010
    Location
    Ceres, California
    Posts
    2,525

    Re: Shopmaster 300 troubleshooting

    An ohmmeter can only find out if a SCR is shorted and the gate is intact.
    R90 is in the collector of Q13. If R90 is burnt Q13 maybe bad. Q13 is in the remote voltage / current path. It could have been damaged by a shorted foot control or feeder cable.
    Put the welder in panel control to bypass Q13. It may be necessary to remove 13 if it is shorted out. This should allow welder to work in panel control. The panel control signal goes through Q13 and then out to the remote control and selector switch.with the remote selector switch the panel signal goes around Q13, but it is still in circuit and can cause problems if shorted.
    I hope you sanded the cap terminal AND the buss bars. Then put a thin coat of aluminum connect grease before assembly. Other wise the connection will fail and arc out again after a short while.

  9. #9
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,575

    Re: Shopmaster 300 troubleshooting

    Quote Originally Posted by ELake View Post
    Cool thanks

    Resistor in question is R90, appears to be a 1k 1/4 watt. How critical is accuracy? Was going to replace with one from radio shack.
    Image is very difficult to make out and I was reading it as R99 (between R98 and R168 ?) but if in fact it's R90, it's a 1/4W, 100ohm and should be matched. ccawgc will have all the information you should need.
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    SA-200 Blackface Code# 8638
    Star Jet 21-110

    Two term limit - one in office, one in jail.

  10. #10
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Quote Originally Posted by ccawgc View Post
    An ohmmeter can only find out if a SCR is shorted and the gate is intact.
    R90 is in the collector of Q13. If R90 is burnt Q13 maybe bad. Q13 is in the remote voltage / current path. It could have been damaged by a shorted foot control or feeder cable.
    Put the welder in panel control to bypass Q13. It may be necessary to remove 13 if it is shorted out. This should allow welder to work in panel control. The panel control signal goes through Q13 and then out to the remote control and selector switch.with the remote selector switch the panel signal goes around Q13, but it is still in circuit and can cause problems if shorted.
    I hope you sanded the cap terminal AND the buss bars. Then put a thin coat of aluminum connect grease before assembly. Other wise the connection will fail and arc out again after a short while.
    Makes sense, 14 pin remote to s-21 feeder has been electrical taped/spliced ever since I've owned it

  11. #11
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Quote Originally Posted by duaneb55 View Post
    Image is very difficult to make out and I was reading it as R99 (between R98 and R168 ?) but if in fact it's R90, it's a 1/4W, 100ohm and should be matched. ccawgc will have all the information you should need.
    Yes it is between r98 & r168 and is 100 ohms (oops)
    Last edited by ELake; 02-23-2012 at 10:20 AM.

  12. #12
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    Got it put back together, fan spins up. I'm not able to use it in CV right now due to a broken feeder pin but in CC I noticed that no matter what amperage setting I put it on it is always at maximum. 1/8 rod was glowing red after I struck an arc.

    Going to test the amperage/voltage pot and chase it back down..good thing it is easy to tear apart

    I saw where another user had a similar issue and it turned out to be a rectifier. A forum member hooked him up with a manual which I'm guessing is more advanced than the one from miller - the owners manual says replace PC1 or HD1. I'm going to test HD1 first with directions from the other thread PIN 1 & 3 with connector disconnected and power off should read 1500-2000 ohms

  13. #13
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    HD1 is OK.

    Does anybody have a tech manual for this? My serial # starts with KC. Instead of posting on here after every move and looking for more suggestions, I could work through the advanced drawings in the tech manual and troubleshoot easier. My email address is emlake@gmail.com

    Thanks
    Shopmaster 300 w/ S-21 feeder
    Single ph converted CP-250TS w/ S-51E feeder
    SP125 Plus
    Spectrum 375 xtreme
    7x12 Kalamazoo Bandsaw
    Clausing DP

  14. #14
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,575

    Re: Shopmaster 300 troubleshooting

    Give Miller Customer Service a call (920-734-9821) with your full SN and ask them if they'll email you the Technical Manual for it. They're generally willing to do that for machine owners.
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    SA-200 Blackface Code# 8638
    Star Jet 21-110

    Two term limit - one in office, one in jail.

  15. #15
    Join Date
    Feb 2012
    Posts
    10

    Re: Shopmaster 300 troubleshooting

    I got it working - transistor Q3 was burned out causing Q13 to not operate properly. When in CC/AC the remote switch feedback wasn't being routed properly in pc1.

    Big shout out to ccawgc for the assistance! His first reply nailed it!!
    Shopmaster 300 w/ S-21 feeder
    Single ph converted CP-250TS w/ S-51E feeder
    SP125 Plus
    Spectrum 375 xtreme
    7x12 Kalamazoo Bandsaw
    Clausing DP

  16. #16
    Join Date
    May 2008
    Location
    Orange, TX
    Posts
    11,575

    Re: Shopmaster 300 troubleshooting

    Awesome! Good job in the fix.

    ccawgc does know his stuff.
    MM200 w/Spoolmatic 1
    Syncrowave 180SD
    Bobcat 225G Plus - LP/NG
    MUTT Suitcase Wirefeeder
    WC-1S/Spoolmatic 1
    HF-251D-1
    PakMaster 100XL
    SA-200 Blackface Code# 8638
    Star Jet 21-110

    Two term limit - one in office, one in jail.

  17. #17
    Join Date
    Nov 2009
    Location
    Hellinois
    Posts
    4,776

    Re: Shopmaster 300 troubleshooting

    Tagged

    for reference
    "Where's Stick man????????" - 7A749
    "SHHHHHH!! I sent him over to snag that MIC-4 while tbone wasn't looking!" - duaneb55
    "I have bought a few of Tbone's things unlike Stick-Man who helps himself" - TozziWelding
    "Stick-man"

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
RSS | Home | Penton Media | Contact Us | Subscribe | For Advertisers | Terms of Use | Privacy Statement