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330 a b/p HF Problem

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  • Aeronca41
    replied
    Ahhh--what a difference the right diagram makes! There is a fuse in the HF circuit in that model, but not in the other (models') diagrams I looked at. Without a manual and pictures of physical layout, I can't tell you where the fuse is but if you look at the schematic, upper left, right where the power lines come in to the main transformer, there is a switch S1 (the POWER switch), with three wipers tied together with a dotted line. The later models only had a 2-wiper power switch, and only one fuse there. You are looking for the fuse on the right (looks like F1) in the schematic diagram. So, you could have a blown fuse, a bad connection, or that portion of the POWER switch could be bad. Locate and check the fuse, and then ohm out the POWER switch if that's not it. I'm betting on the power switch being flaky--and the fuse may have blown due to current surges as it flaked in and out. Also, if the fuse looks OK, you still need to check it with an ohmmeter. I have found a number of very old fuses over the years that looked good but were not when checked with an ohmmeter--I think the end of the fuse element must get internally disconnected from the end caps somehow due to age and vibration. Never bothered (or had time) to take one apart to see what happened.

    And, as I continue looking at the diagram, there is something really strange. It appears that for whatever reason, they have placed the fan motor in series with the HF transformer primary. Does the fan work? It looks like a bad fan could shut down the HF. Not something I would have expected. Ya gotta love sleuthing through these old monsters! I have to wonder if there is a mistake in this diagram, though. Seems the fan would only run while HF is active, and no other time, which just seems wrong. If I were guessing, I'd guess the fan is NOT supposed to be in series with the HF transformer, and there should be a connection dot on the diagram where the line that runs to the right from the top of the fan motor crosses the line coming down out of the left fuse (looks like F2). That would make a whole lot more sense.

    Ryan, don't tell Helga I called her a monster--I know how sensitive she is about her weight!
    Last edited by Aeronca41; 06-03-2019, 07:33 AM.

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  • ryanjones2150
    replied
    There's probably another diagram on the inside of the lid there. Wayne will know what it says. To me, it looks like someone spilled their bowl of ramen noodles.

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  • Jmcghee
    replied


    Same idea but looks older to me. Also noticed the diagram for the first time when I grabbed that pic:

    Attached Files

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  • ryanjones2150
    replied
    Does she look like this when you lift her skirt up in front?
    Attached Files

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  • Aeronca41
    replied
    Pretty far for in-person assistance. :-)

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  • Jmcghee
    replied
    I’ve got a machine shop, but no oscilloscope unfortunately

    I’m in central Illinois

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  • Aeronca41
    replied
    That sounds good. I'm almost positive the diagram I have is not the right one. I would suspect it's awfully close but better to be sure we have the right one. If they send you one, send me a PM and I'll give you an email address to send it to. (Actually, I just found it's in a PM thread when we were working on your other welder.)

    STANDARD is good--takes more stuff out of the circuit. I'm guessing you're going to find a bad connection or something similar--the switch, transformer, output coupling coil, a couple of caps, and wiring are about all there is that's unique to the HF circuits. You said you're already changed out the caps, so that's probably eliminated. If there's a short in the transformer, that may be more difficult to find--and would be a very unlikely, but not impossible, failure. Might find it with an ohmmeter, but it may require an oscilloscope and a pulse generator, which most people don't have lying around the garage. I may have asked this before, but where are you located? I'm in upstate NY.

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  • Jmcghee
    replied
    Originally posted by Aeronca41 View Post
    What does your meter read when you just touch the leads together? 0.5 ohms seems high for a working switch. Maybe it's just your meter or leads. If the switch reads the same as you get with the leads shorted together, then I think its probably OK.
    The meter reads the same (.5) just touching the leads together with nothing in between.

    Ill call tomorrow and verify the serial/manual/year. The machine “feels” and looks old (similar to my other welder which miller verified as 1966) for whatever that’s worth. Not sure if this helps date it, but it does have the gold star sticker on the front.

    I ran a stick bead and it purrs like a kitten. Similarly, it’ll scratch start tig (dc carbon steel) beautifully as is... just no HF start.

    I guess I should’ve added that I don’t have a pedal so that’s not part of the equation (remote switch is in “standard” and nothing plugged in). I do have a remote contactor and have tried everything with and without it with seemingly no difference.


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  • Aeronca41
    replied
    Ohm’d the switch out, & it appears to me at least to be working correctly. .5 in both directions, and wiggling it around with the meter leads clipped didn’t create any sort of intermittent failure.


    What does your meter read when you just touch the leads together? 0.5 ohms seems high for a working switch. Maybe it's just your meter or leads. If the switch reads the same as you get with the leads shorted together, then I think its probably OK.

    I downloaded a schematic diagram. But, when I think about it, I'm not confident the diagram I have is correct. The "single letter" serial number seems to me to relate to a really old machine but the only serial number range I can find that fits in the list of documents I find on the web site implies that the diagram I'm looking at would be for one of the newest machines. So, before I have you go poking around in there, and finding something unexpected and surprising (perhaps in a bad way), please call Miller, give them your serial number, and ask if O340P_MIL is the correct manual for that serial number. I have a hunch it isn't. If not, ask them to email you the correct manual and you can forward it to me. They are really good about that.

    BTW, I assume this thing will stick weld OK. Remember the manual warns against turning on the HF when stick welding--no arcs to the operator desired! Please verify stick works first if you haven't.

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  • Jmcghee
    replied
    It does yeah... I reset the gap to .009 at the get go

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  • BukitCase
    replied
    Forgive me for chiming in when I know exactly jack squat about this particular machine; does its HF by any chance get generated by a spark gap? ... Steve

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  • Jmcghee
    replied
    Ohm’d the switch out, & it appears to me at least to be working correctly. .5 in both directions, and wiggling it around with the meter leads clipped didn’t create any sort of intermittent failure

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  • Aeronca41
    replied
    Originally posted by ryanjones2150 View Post
    Case in point, my Helga had a bad start-off-continuous switch.
    So, THAT'S where I heard of those switches going bad before.


    "Serial is W527655 which I believe puts it at 1970. Aeronca41- you actually walked me through a problem with my other welder (wound up being a diode) about a year ago... not sure if you recall."

    The name was familiar, but I had forgotten the welder....things don't stay in the old brain as much as they used to, but I never really had that good of a memory--which my wife often noted..... ;-)

    Will take a look at the drawing for that serial number later today or this evening.

    If you ohm out the switch, be sure to use clip leads so you can maintain good contact while you wiggle the handle around and see if the ohmmeter jumps. May be intermittent as Ryan says.

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  • ryanjones2150
    replied
    I discovered mine was the problem causing intermittent fluttering of the HF. Set it to continuous and went to wiggling the switch and replicated the problem. I think I actually have a spare switch laying around out there in the shop. Mine is a 74 model.

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  • Jmcghee
    replied
    Serial is W527655 which I believe puts it at 1970. Aeronca41- you actually walked me through a problem with my other welder (wound up being a diode) about a year ago... not sure if you recall.

    I hadn't really considered that the switch could be fried, seems like a pretty simple contraption to go bad. I have a meter, and what I’d call a base-level knowledge of electrical (wired my shop, RPC, 460 transformer, etc)

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