By ssbn727
Date 01-24-2008 10:07
Edited 01-24-2008 10:12
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Hi mad380se!!!
First of all, Weldcome to the forum!!!
If everything is like you describe, then it's definitely somewhere in the High requency circuit... Like Dave mentioned, it's more than likely the HF capacitor that's shot but, make sure the HF transformer is working properly before one assumes that it's the capacitor... Most important is to have someone that is competent in troubleshooting electro- mechanical & electronic components because, if the person diagnosing the components doesn't follow the schematics properly when testing under a load, that person is sure gonna get zapped!!! In other words, if you do not know how to troubleshoot components with electricity going through it - for heavens' sake, leave it to someone that does!!! Let us know how you make out, and all the best to you. Oh I almost forgot, make sure the spark gap is correct according to factory specs, nad check hte surface of the gap electrodes to see if there is any pitting because, one might have to also replace the electrodes in order to get optimal HF output.
Respectfully,
Henry
You should see an intense blue sparking at the points where You set the .008" gap. As Henry points out You need to check the rest of the HF circutry as well, and it operates at extremely high voltage, so it is not a job to be taken lightly. The capacitors are not cheap, I am trying to locate a direct source for them, I think I have determined the manufacturer but havn't tried to buy any directly yet. If anybody has a source other than Miller, I would like to know.
Well, for your other unanswered question:
No, you should not be able to scratch start on A/C with a sinewave machine. I do not know if that is possible even with a conventional squarewave machine, but it would be possible with a good inverter squarewave machine (the waveform needs to be -really- "square" for the arc to be maintained past the zero crossing). I know my Dynasty supports lift-arc for A/C, and the HF isn't continuous either.
All great advice. I don't want to step on anyone here, and this probably won't help, but:
Could there be anything conductive between the the points (gook, dust, or worst of all grinding dust containing metal whiskers). At the voltages of the HF, just about anything is conductive (even AIR, because this needs to produce an arc to jump through it). Just one tiny whisker of grinding dust (just pass a magnet of the dust near your grinder, and you'll recognize it from the furry friend you just made), could short the points and stop the spark.
So, the gap points need to be clean, and dry. If they're exposed to the ventilation in your machine (as they are in mine), and not sealed, regular blowing out with air may be required. If you must, its best to clean them with electrical contact cleaner, or something that leaves no residue, like acetone, but keep the flammability issue in mind with something that is supposed to spark. :)
There are a number of other places that the HF could be lost to ground, but if you're not seeing a spark between the gap points (in a dim room), then the problem is somewhere within the HF circuitry. Now, when you say you hear noise . . . I've always associated something between a buzzing and ticking, as coming directly from the spark in the gap. The arcing sound is pretty distinctive (these are microscopic sized thunderbolts afterall), and if you're hearing it, but not seeing a spark at the gap, then it could be arcing elsewhere (not good).
Dave:
My company deals in electronics. I you can get me a part number for the capacitor, I should be able to get a datasheet, and cross reference a replacement. Maybe even source something.
all great posts so far, alot of good info. So, I got home from work and decided to dig a little deeper. I noticed when i turn off the lights (with the covers off on the machine) i could see arcing or a glowing coming from the HF transformer when i press the foot control. I'm assuming that this may not be a good thing? ALso, when i first gap the points then turn the machine on and press the pedal there is arcing at the gap points. Then the next time i press the pedal nothing happens, no spark at the points. So, the problem may be the transformer then? I spoke with an electritian in work and he said that the transformer really shouldnt be arcing or glowing. What do ya think?
Hummm. Aurora Borealis inside your machine. :)
I don't know how to interpret that, but I do know that voltages that create that effect can put you in a world of hurt.
There definitely should not be any arcing other than between the gap points, and coming from your tungsten.
A constant but ridiculously dim "glow", could be a corona discharge. Not that I'm telling you to put your nose inside the machine, but do you smell ozone?
I don't know if the voltages in an HF circuit are high enough to support this, BUT, I do know that the energies available in the HF path are VERY low for safety purposes, so it doesn't take much of a current leak at all, to stop it from working.
Personally, I would find any glowing parts, and liberally coat with dielectric varnish, but I'm not saying that would help you . . .
Be sure that the transformer is clean, just as rlitman mentioned about the points and the mounting board, this goes for all the components & wires, it doesn't take much to conduct this high voltage.
Hey there, thanks for the help everyone. I ended up replaceing the HF transformer. Looks like miller doesnt make my orginal hf transformer, but they had a replacement. The machine works great now. $200 smacks from airgas and I'm on my way.
rlitman, the cap specs are .02 MFD 10000 volt. I copied the complete info from one I saw in a picture of another manufacturers HF board. CDM F2B .002 MFD 10000PWV 6.2 Amps 1 MHZ F2100B202JM 0036 I suspect the manufacturer is Cornell-Dublier. For a picture [of sorts] look at the parts diagram for any Miller TIG welder or HF box. This is on the back burner as it is not for My primary machine, but any help would be appreciated.
Ok, the .02 threw me off. Miller's diagrams show .002MFD. That's 2000pF for researching this one.
The part number F2100B202JM is Cornell-Dublier, and looks to be around $290. Ouch.
It appears as if Cornell-Dublier is no longer making rectangular mica caps, at ratings above 8kv, so I don't think a new direct match is available.
They do make -cylindrical- mica caps at 10kv and above though.
292100B202JO0 looks like a good fit at 10kv peak rated, and 13A @1Mhz
293150B202JO0 is rated at 15kv peak, and 20A @1Mhz
294200B202JO0 is rated at 20kv peak, and 22A @1Mhz
I'll try to look into pricing for these crosses tomorrow.
Thanks, .02 was a typing eror on My part as You figured out.
Ok, the 292100B202JO- is a cylindrical cap, approximately 2.5" in diameter, and also 2.5" in length.
The trailing number (0, 1, or 2), is for the number of diamond shaped mounting flanges. Without flanges, it has a 1/4-28 threaded hole. It is of the axial style.
The specs look good to me, but without actually seeing the board, or how the cap is hooked up (its a little unclear in the manual from Miller), I couldn't guess if this would fit or not. The large size might also be a problem. The diagram is also not clear if an axial cap could work.
Unfortunately, the 10kv rectangular caps originally used appear to be long out of production. They are available, but ouch . . .
Anyway, allamerican.com (with whom I have no affiliation, and no prior dealings) has a few of these cylindrical caps for just over $100 each. Yeah, its a lot for a single cap, but this is way outside of the norm for a typical cap. I don't actually deal with the electronics portion of my company, but when I showed the specs to someone in purchasing who found it for me, I got a whole lot of strange looks and questions about such a weird part.
At $100 ea. it probably isn;t worth reworking the board to make them fit, My machine uses 2 of them. This is an odd value cap, but every HF machine and box I have seen the schematic for uses them. Thanks for Your help.
Well, that was for the closest current production replacement. Those things can be pricy.
I've seen DIY HF circuits done with "doorknob" transmitter caps. If you're not looking for an exact fit, these can be had for less.
Have a looksie at eBay Item number: 250210872369. That is 40kv and 2000pF for $28 shipped.
Also, remember that caps are additive in parallel. So, so long as you have a high enough voltage, you could get away with ceramic caps (much cheaper than mica), and just use a
few.
eBay Item number: 250211175756 is for six ceramic caps rated at 15kV, but only 1000pF. All for around $20
And these are really small enough to fit anywhere at 5/8" diameter, and nearly flat.
I do have to say though, that there are a lot of counterfeit parts coming out of China (where these eBay items are from), so I would be wary.
For a project for myself, fine, but -I- wouldn't install these in a customer's machine without some sort of testing (say hooked across the leads of an 8kV neon transformer for a few hours, before verifying capacitance).
Thanks for the suggestions, these are for an old Airco that is the same as a Miller 360 A B/P. I now have a Sincrowave 300 in good shape, so I won't mess with the old machine untill I get some "spare" time.