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Syncrowave 300 - HF runs constantly.

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  • #16
    holy smokes, that an expensive part.

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    • #17
      Originally posted by Sked View Post

      OK. That sounds more like where I thought I'd be going. I may take a shot at replacing them, but looking into the PC2 boards raises another question. My machine has an older 039 195 board (mine is actually marked 039 196) as shown in the parts list from a 1975 owners manual. The Service Parts Manual I received a couple days ago is dated 1991 and does cover my serial number machine. On the subject of the PC2 Board the manual states for 052 790, the only PC2 Circuit Card shown, "This Circuit Card Replaces All Previous Circuit Cards And Is The Only Card The Factory Recommends Repairing". I notice there are no transformers, relays, or thyristors on this newer Circuit Card. I'm wondering if updating is the way to go. Thoughts?
      Could be, just seems like a lot of money. I'm not afraid to spend good $ on quality welders, (only Miller, Hobart, and an old Lincoln Century from 20+ years ago around my place) but it kills me to spend $500 on repairs when the individual part that's bad is only a few bucks. Of course, the key is finding the right component to replace.

      Don't know about Miller-not enough experience on different machines, but in the world I came from such guidance often meant there was an unreliable design that got updated. Like battle plans that don't survive first contact with the enemy, sometimes designs that look good in plant don't fare so well in day-to-day service-it can happen to anyone-less likely if you're good. (See comments/threads on Longevity-it had my interest for about 10 seconds, then I bought a Dynasty 200.) If you plan to use the welder a good long time, maybe it's worth the $500; the upgraded board may prevent future problems. Of course, you could spend the bucks then have the other board go bad-always a risk to be weighed with an old machine. Concern is that without actually troubleshooting the machine, it would be a real bummer to spend the $ and then find a shorted wire somewhere. Do you, or someone you know, have any troubleshooting/repair skills, including down to the component level on the board? If it's Q301, the part is probably about $5 (just a guess). Doubtful you can get it under the Miller part number at this point, but it's a generic part. Allied, Digi-Key, Mouser, etc. should have it, going by the specs on the parts list-should be able to find something that will work.

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      • #18
        Originally posted by Aeronca41 View Post
        My next guess would be a shorted Q301 Thyristor on PC2.
        AND THE ANSWER IS:

        The problem of the constantly running HF was caused by a bad Q304 THYRISTOR on the PC2 Circuit Board. Thanks Aeronca41 for pointing me in the right direction.
        And to explain completely, the HF problem and the dirty welds I mentioned in the original description of my problem were not related. The dirty welds were caused by a leak in the gas hose running to the torch.
        Thanks to all for your input.

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        • #19
          Outstanding! Tough when you have two simultaneous problems to find, but you did it.

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          • #20
            Low and behold as most of you all know, the syncrowave 300 has had its issues when it comes to the high frequency
            l have been able to let my girl sit alone in the corner for years until now and am trying one more time
            There is no tag to tell the serial number but after several conversations with Boone at Miller in the Tig trouble shooting department, it has been narrowed down
            He suggested ordering a service tech manual TM-350
            Not being a factory service center, they would not sell me one but I was able to find one on line and it is on its way
            The conclusion at the moment is either the high frequency transformer, or the capacitors are failing once heat becomes a factor
            When cold, I have HF on start and continuance
            When welding DC straight and the HF is in start, I have a perfect arc and the machine seems to be welding fine
            As the minutes go by, the HF arc begins to get shorter and shorter until it goes away completely and then I have to use the lift arc option
            I can tell that at least one or more of you involved in this thread knows how to read the schematics, something of which I admit cannot do
            Where I stand at the moment is I have unhooked all of the wiring at the lower junction strips and have cleaned the the CR 1 and CR 2 relays
            My plan is to relocate the relays into a separate box that I will fabricate here so that they will not be filling up with dirt and straighten out the wiring from the rats nest that is was
            The majority of the wiring is almost impossible to read due to the pour stencil printing
            As an example, telling the difference between the number 31 and 81 wires is a hair puller
            If I have the wires matched to the numbers, some have to be separated on their own circuit to be the correct path rather than be all tied together
            I have several that I need help separating correctly
            Numbers 31, 32, 81, 61, 68, and 86 that come to mind at this moment
            I have hope than someone can get me headed in the right direction before I burn something up that I will regret
            Thanks in advance, Randy
            Last edited by dt38k; 07-10-2019, 10:56 PM.

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