Lincoln IdealArc Tig 250 HF Problems

[treed67]

Ok guys, I got a question. I just bought a used Tig 250 that welds fine, but the HF isn't working. So far I have:

Checked HF Capacitor to be good.

Checked the spark Switch

Checked contact gap

Checked for shorts to ground.

Checked that I am getting 115v to the primary side of the high voltage transformer (with the transformer disconnected.) The problem is that when I connect the primary leads to the high voltage transfomer, I only have around 3 or 4 volts coming into it.

The primary side of the hv transformer measures around6 ohms and the secondary side measures about 8K ohms.

Do I have bad hv transfomer or could something else be breaking down when the transfomer is connected?

[kazx9r]

6ohms doesn't sound good, I'm not an expert but those are the two little transformers sitting on the right lower side?

Here's my thread,

http://weldingweb.com/showthread.php?t=110581

If you call Lincoln Bill is the guy you'll get redirected too, not very impressed with there service.

Member ccawgc knows his $hit.

[treed67]

Kazx9r, I had already read your thread. The high voltage transformer is the one setting on the 3 plastic insulators (left front corner of machine). Its right beside the HF chokes, HF capacitor, and HF transformer (big Coil with small inner coil). I have a feeling 6 ohms isn't right either, but was hoping someone had tested one before or know what the ohms should be. One wire that feeds it comes from the spark switch and the other comes from the main transformer. If I check voltage, I have 115V coming to it as long as it isn't hooked up. When I hook it up, it drops to like 2 or 3 volts. That really leads me to believe that it's the problem. I just wanted to know for sure how to find out as that transformer is like $250. I have heard of people using ones from neon signs and stuff. If that is the problem...does anyone know of a source for a cheap transformer that will work. From my research, It appears it's 115v in and 3000v out. Do you need to stay close to 3000v on the output?

[kazx9r]

Now I know the one, I took it out to test mine, I recall somewhere in the kilaohm range on both but will have to recheck to be sure. $250 seems kind of high for such a small transformer, I don't know where one would get that. Can't be too much wattage in there, the wires are like 14 gauge.

[treed67]

Well, I figured out more. I removed the covers on the relays (timer board). The gas relay was kicking in but not the hf relay. I pushed it with a screwdriver and bam the points start arcing. The problem is in the board as I checked and the relay isn't getting any power. The only confusing part it that I had 115 volts to the transformer as long as the transformer wasn't connected. Must have been backfeeding from somwhere. Anyone have any experience with reparing a timer board? It's $288 online...so I think repair is best option.

[ccawgc]

The 115 volts you are seeing, comes from a bypass filter across the relay contacts.
As long as the circuit is open you will see the 115 volts. 6 ohms is about right for a 115 volt AC transformer coil.
Now before you think about repairing the pcb, measure the AC voltage at plug 2 pins 6 and 9.
should have little or no voltage until remote control is closed. Always turn of HF or unplug the primary when testing with a DVM around the HF system. The HF will kill your meter.
You must have 115 volts at this point or the timer pcb will not work at all.
This supplies the power to the 24vdc and 10 vdc power supplies.
If the weld mode switch has a bad contact it can keep the timer pcb from working.
wire 209 gets its power from from that switch. No power on wire 209, timer does not work.
No HF, NO gas flow.
There is a good machine diagram in the owners manual IM-315A Plus pcb diagrams.
Functions to the plugs on the pcb are the same. some of the parts on the pcb may be a little different. Make sure the pcb has all its inputs before thinking the pcb is bad

[treed67]

Thanks a bunch ccawgc. I will check what you suggested. I think that I must be getting 24v to the pcb because the gas relay is kicking in....although I have tested the pcb the best that I can and am not finding a bad diode or resistor. Also I cannot find the 315A manual. The only one that I can find is 315 and the print is hard to read for the pcb board. Does anyone have a location for 315A?

[kazx9r]

http://www.lincolnelectric.com/en-us...r-manuals.aspx

Sorry I can't help much, my thing is shot...so not very motivated to do anything.

[treed67]

Well, I'm completely confused now. I have tested the pcb the best I can and don't believe anything is wrong with it. Here is the kicker. I flipped the inert gas to stick and then back to inert gas and it started working. It would worked everytime for 10 or 15 times and then quit. Sometimes it would be a little delayed when I hit the pedal. Now the only way that can make the high frequency kick in is....hold the pedal down and flip the switch to stick and then back to inert pretty quickly. I twill kick in for like 2 or 3 seconds and then back out. This make any sense to anyone? I don' think the pcb is bad since it worked a few times. The problem on the pcb is that the negative side of the 12 volts isn't making it to the relay. It's making it all the way to the switching transistor, but never on to the relay. I'm assuming something causes a drop of the current on the 3rd leg of the transistor to make it switch. The voltage never drops and it never makes up a connection.. Wish I would have tested it while it was working to see exactly how it works. Please help...this thing is driving me nuts.

[kazx9r]

The relay on the timer board?

[treed67]

The HF relay on the timer board isn't getting the negative side of 24 volts. It is stopping at the transistor before it gets to the relay. I believe the transistor isn't getting the correct signal to close it's switch....but signal comes from the IC (operational amplifier) and I can't figure out the schematic to see it the IC is getting its correct signal or not.

[treed67]

I think I have found the problem on my Timer PCB. I think the capacitor C105 is bad. Here is what I have come up with. If I hit the pedal after it has been turned off for a while, it will take about 15 seconds for the HF to kick. If I get back on the pedal pretty quickly after releasing, It starts immediately. If I wait longer it turns into a delay. I put the volt meter on C105 and monitored it. Once the voltage on C105 gets up to 6.4 volts the transistor will switch and throw current to the relay. After you release the pedal, the voltage starts falling pretty quickly on the capacitor all the way down to 1 volt. The other caps maintain their voltage. If you hit the pedal again, the HF will kick in once the cap is charged back up to 6.4 volts. The capacitor is 25V 16uf and it looks like a tantalum capacitor to me. Is it ok to replace it with an electrolytic capacitor that isn't the exact specs. Maybe a 15uf or a 22 uf? The 16uf tantalum cap is going to be hard to find and cost quite a bit more.

[kazx9r]

Interesting you run this by ccawgc

[treed67]

Nope, no on ever really offered any ideas on testing the actual PCB. I just studied the schematic and went to testing. I actually welded with it a little yesterday and it works once the drained capacitor charged up. Just gotta hit the pedal a little early. Works in the start mode and continuous. Should be good once my capacitor gets here. I actually have someone coming to look at my big Air Products (Miller) 300 today. That thing has been a good one, but a huge beast. I think I'm going to like the Idealarc though.

[ccawgc]

Looks like C 105 is the preflow timer. When these caps get old they take longer to charge up to the point where the transistor turns on. So it takes longer and longer for the HF to fire.
Try to find a cap with similar ratings So the charge curve will be close. Electrolytic caps are not the best choice for timing circuits. Tantalum is first choice, Second choice are the orange drop or the polyester and yellow ones.
If you want to disable the preflow timer, just replace the cap with a resistor that has a 6 volt drop on it. There are a bunch of mail order electronic suppl houses that can supply what you need. Newark, digikey, mouser ect.

[treed67]

Thanks a bunch. It seems to work fine..just have to wait for that capacitor to charge up. I ordered one with idential specs in tantalum. I should be good to go soon. Thanks again.