330 a b/p HF Problem

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

Hey guys-

I just picked up a 330 a b/p to replace my old(er) Dialarc and am working on getting it all set up. I wired everything in, set up the torch, ground, etc & fired it up. HF was in the “start” position and it fired up as it should, & quit when I struck an arc. After working once on that initial test, the HF won’t kick on at all under any settings. The caps were leaking some so I replaced them with “known good” caps (same exact model from a machine with functioning HF) and nothing changed at all. Still no HF in start or continuous, ac or dc. Is there something else (fuse etc) in that circuit I could’ve fried after that first initial test? Something else I don’t know about?

Thanks in advance!

[Aeronca41 Senior Member Find all posts View Profile Close Aeronca41]

Need your serial number to look at the correct diagram, but picking one at random, I don't see any fuses in that circuit. The HF circuit is not very complicated (especially in continuous mode--that mode takes a LOT of parts out of the circuit), and I would first suspect bad contacts in the "START-OFF-CONT" switch. Have heard of those switches going bad before. How are you at electrical troubleshooting? Do you have a digital multimeter and know how to use it? If so, disconnect the wires from the switch (be sure to label them first!) and then ohm out the switch with the meter. That is not a foolproof test, because I have seen cases where the contacts fail to carry enough current to really work, but test OK with an ohmmeter. Not common, but it happens. Are you confident and safe working around live circuits? Do you have the manual? Do you know how to read schematic diagrams? There are plenty of people here who can help you through it if not.

[ryanjones2150 Senior Member Find all posts View Profile Close ryanjones2150]

Case in point, my Helga had a bad start-off-continuous switch.

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

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)

[ryanjones2150 Senior Member Find all posts View Profile Close ryanjones2150]

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.

[Aeronca41 Senior Member Find all posts View Profile Close Aeronca41]

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.

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

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

[BukitCase Senior Member Find all posts View Profile Close BukitCase]

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

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

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

[Aeronca41 Senior Member Find all posts View Profile Close Aeronca41]

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.

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

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.

[Aeronca41 Senior Member Find all posts View Profile Close Aeronca41]

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.

[Jmcghee Junior Member Find all posts View Profile Close Jmcghee]

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

I’m in central Illinois

[Aeronca41 Senior Member Find all posts View Profile Close Aeronca41]

Pretty far for in-person assistance. :-)

[ryanjones2150 Senior Member Find all posts View Profile Close ryanjones2150]

Does she look like this when you lift her skirt up in front?