Problem With Unitweld Hitbox Pulse TIG Welder TIG200P

[bullet308]

Hi:

First of all, allow me to concede that I was a dumb ass...I bought this thing off of eBay, trying to shave off a few dollars versus a new one...this one is apparently a return, and I think I know why it got returned...This is a link to the new one I should have bough...

https://www.ebay.com/itm/TIG-welding-machine-200A-inverter-tig-pulse-welder-ARC-digital-control-3-IN-1-/152619468542

This is a rather sophisticated little TIG  machine, highly programmable in terms of giving very precise control over the current going into the workpiece. This, of course, makes it obscenely complicated by the standards of a welder. At least five or six circuit boards.  :-/

So, I plug it into a known-good 50a 220v outlet and it powers up normally. The fan makes the requisite wooshy sound, the front panel lights up and seems to be behaving normally. So I set it to MMA ("stick") welding mode, hook the ground clamp up to the utiilty trailer I am going to weld up, swing down my helmet, and...

<bzt>...makes a welding noise for about 1/50th of a second, and the unit shuts down.

I cycle the power switch...nothing. I unplug it for a while, then power it back up, and the fan and front end power up normally for about a minute, then it shuts itself back off again.

Now, I have it plugged in with the covers off...same behavior: powers up for a minute and then powers itself back off.  When I cycle the power switch now, I hear a faint <tick><tick><tick> sound from the lowermost board, which is the power supply. It sounds a lot like an old mechanical clock running.

I leave it plugged in and leave it for awhile and it powers back up for a minute and shuts down. Interestingly, if I leave it powered down for just a minute or two, it will come on for a few seconds and power itself back off...As if something is heating up and then tripping, and then cooling and resetting...?

I have written the manufacturer but have no idea what kind of factory support I am going to get for this thing and have already resigned myself to having to repair it. If somebody could provide some ideas what these symptoms correspond do, I would very much appreciate it.

-Tom

[bullet308]

Okay, Lets see if some photos will encourage folks to suggest on how I might troubleshoot this thing...

The only anomaly I have spotted so far was the otherwise unmarked black box that is denoted as RX1 on the boards silk screen...I would have thought it was a relay at first glance, but it is apparently not. I was thinking it might be a diode, but what the notation RX1 indicates, I do not know.

The covering over whatever is under there is loose...At first, I thought it was a bad solder job because the whole thing seemed to be lose and rocking side to side on the board, but it turned out it was just the cover...

Whatever that component is, it only has two leads running into the board and when I check it with the multimeter, it shows open.

It takes 220v mains power and breaks it down into a variety of different voltages for different systems, but whatever is tripping, it is shutting down everything instantly,...I am thinking it is related to RX1 or the big relay that is right next to it, which is adjacent to the lug where the mains positive wire comes into the board. It then runs through that big blue ceramic cap, then RX1, then the relay. 

The relay seems to be the most likely thing to be making the clicking sound I hear, but what does RX1 contribute to the problem...?

[bullet308]

Added an inverted version of the back of the board to make it easier to trace things and have marked some of the more critical parts.

I would have though RX1 would be a diode, but I have never seen a board with components denoted as "RX"...

[Andy Watson]

Without a schematic it will be very difficult to fault-find. It's a daunting task but your best bet might be to trace-out the circuit on that board - otherwise it's guesswork and luck.

My guess would be that RX1 is a thermistor. When you power-up it prevents high surge currents as the main capacitors charge. After a short while RX1 will/should be shorted-out by a relay - probably that blackbox with the label "C" on top in your first photo. My guess would be that this relay is not operating correctly and therefore not connecting the "main" power to the circuit.

Does this bear any resemblance to your unit?
http://www.9722356.ru/_ld/0/10_278_AC_DC200-31.pdf

[bullet308]

I cant access the full manual at work, but it reads like it is similar in concept (all I could get was the Google cached version...will try again when I get home.

The importers were kind enough to send me a manual that kinda' sorta' had a diagram in it, but it it was obviously simplified greatly and had no labeling to the parts depicted. I will upload when I get home as well.

The symptoms include the machine powering up normally from cold start, running about 1 minute and shutting back down again. The less you wait before restoring power, the shorter the time it runs before shutting down, as if something  is heating up and shutting the power off, presumably at that relay.

If you power it back up before it "resets", you hear a faint clicking from something, either the relay or that mystery RX1 part...I don't see anything else that could account for it.

[bullet308]

Let me ask another question while I am at it...

Could this have something to do with polarity of the AC mains? I did my level best to follow all provided instructions but could I have things reversed? Would that cause the thermistor or whatever to heat up? I would have though something really loud and expensive would happen if you wired in 240v backwards...

[Andy Watson]

The importers were kind enough to send me a manual that kinda' sorta' had a diagram in it, but it it was obviously simplified greatly and had no labeling to the parts depicted.

That sounds like the manual that I linked to

It does not matter which way you wired the 240V - it's A.C.

[bullet308]

Okay, so at least I didn't smoke it completely...

The manual you linked to is vastly better than the one I was sent...and they are similar machines, but nothing like an exact match...