Old 180 SD HF stuck on

[Tweekster]

I work on old car stuff so I run into this all the time, impurities pure and simple.

See the higher levels of black and orange soot around the weld, that's the impurities burning off. Grind and clean more, even the back side, because once the weld puddle penetrates it'll pick up the backside...

[Tweekster]

it either works or it doesn't.

Push the pedal, get a HF spark, then the arc starts, and the HF spark stops the arc continues.

You can tell by the way it sounds.

[Tweekster]

I weld 18ga to 16ga, 1" to 3"dia. stainless and aluminum tubing quite a bit, and I would have to say the hardest thing is get your bench set up so you can support your hands comfortably and be able to control the torch precisely, move around the tube and keep the tube from rolling on you....

[Tweekster]

1/4" masonite templates, bolted or clamped on with washers for a slight space above the metal to save the template.

[Tweekster]

Thanks, that's kind of what I thought. I have a micro drill I use for RC models, and have plenty of solder wick, so I better get to scraping....

[Tweekster]

After a few of nights of learning and testing, it looks like it's U8, the CD4098.

What methods are people using to remove the conformal coating? Solvent or mechanical means? It seems to be polyurethane based, but I could be wrong.

TIA

[Tweekster]

kcstott is correct.

Per the NEC (National Electric Code) all subpanels must have a separate common and ground running back to the main panel, so all grounds terminate at one point, the main panel. The subpanel needs to have 2 busses installed, one for common and one for ground, and all...

[Tweekster]

And that's why it's been sitting in the corner for 5 years, it cost more to fix than it's worth on the used market. Sad thing is, it's in perfect condition, looks like the day it came out of the box, inside and out.

I'm only selling it for $500 (just the box), if I can fix it.
...

[Tweekster]

Much appreciated! I'll work on it more tonight myself.

I have a good DMM and a scope, just to get my brain wrapped around gates and opamps. I understand the concepts, and have played with a couple of circuits before, just never had to troubleshoot one....

[Tweekster]

I'm at work and need to check my schematic....wouldn't that let the HF turn on with the peddle, but will it ever turn off once the weld is started?...

[Tweekster]

I killed the AC to the HF transformer right at the start, then put a cheapo meter across it to monitor it for a change.

As soon as I turn the power on in either TIG mode the HF is on, the pedal still controls the welding output, but does nothing for the HF. The HF turns off in stick...

[Tweekster]

Finally had a chance to get back on the troubleshooting.

Circuit Board #190772

Across RC1-7 and RC1-8 I got .5 Mohms/40+ Mohms forward and backwards, Q3 looks okay.

Across pins 4 and 6 of OC1 I get 85 Mohms forward and backwards, that looks okay.
...

[Tweekster]

Thanks! I'll give it a shot.

I'm a self taught audio amp guy, so these control circuits are a little new to me.

[Tweekster]

5 years ago my 180 SD had the HF start stick on, and being in the middle of a project, I used that for justification to the Wife to buy a Dynasty 200 DX. The 180 SD has been in the corner ever since.

A friend now wants to buy the old 180 SD if I can fix it. I have the 180 SD Tech...