L-Tec Heliarc 250HF High Frequency Start Problem

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Hi everyone, I've been reading these forums for a long time but this is my first post. I'm a hobby welder, I got into welding few years back with a mig welder but after taking some night classes, I decided I want to dive into tig welding. Last week I bought a used L-Tec Heliarc 250HF Plus welder after successfully tigging both aluminum and steel in the sellers shop. When I got it home the high frequency had ceased to work.  I cleaned the points and set the spark gap, still no luck.  I can't see anything happening at the points. No sparks at all.  I turned off the lights and gave it a go to see if maybe the hf was grounding out somewhere but I didn't see anything. The machine still stick welds fine, and I have both current control with the pedal and gas flow if I use the pedal while scratch start tigging on steel. I tried swapping out tig torches as well thinking my torch was bad and still no luck. I'm hoping someone has a thought about what I can test or try to get this welder up and running well again? Thanks for any and all help.Ryan Sent from my SM-G930V using Tapatalk
Reply:Do you have the manual for the machine? Get one if you can. ESAB may have them online. You can email the tech support if you can't find a manual. I've had good response times from them recently. I just did a quick search for L-TEC Heliwelder 250 and came up with a manual from 1995, on ESAB's site. You mention setting the spark gap, was that spec from the manual? And what did you set it to? If you have the manual, there may be a section in the troubleshooting area related to no HF spark. Sounds like you have a good handle on the TIG procedure, but it doesn't hurt to list all your machine settings, or even a picture of the front panel for the TIG setup.Last edited by redbeerd; 03-27-2018 at 11:58 AM.AHP AlphaTIG-200X Miller Multimatic 215
Reply:Thanks redbeerd, I did get a manual for the machine.  It said to set the spark gap to .025, I used feeler gauges to set it. I'll get a picture of my settings when I get home from work. Thanks again, -Ryan
Reply:Here are few pictures including the nameplate, a pic of the hf assembly and the machine settings. I have it set to A.C., HF set to continuous, balance and arc force roughly at the midpoint, and in tig mode. This was to weld aluminum. Here is the web address of the manual I have been  using. Hope that link works. Thanks, Ryanhttps://www.google.com/url?sa=t&sour...noARl_ja__76L4



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Reply:Thanks for the manual link. It worked. Did you try TIG welding with the HF switch in START mode? Used for welding on steel. Try that first, then the following.So, on page 17 of the manual, section 5 Troubleshooting, part "J".

It sounds like you've tried the first 2 options.  Onto the third if you haven't done so already. Hope you don't have to get to #4. And looking at the schematic on page 18, you'll notice that some items appear to have been written in by hand. I don't see on the schematic where the "HFS" (Hi Freq Switch) is. But, physically, it's on the front panel toward the top and has 3 positions, OFF, START, CONTINUOUS. Page 10 in the manual has a description of it. You should check that just in case. To test you should make sure machine is unplugged, then isolate the switch from any connections and test the switch and the wiring for continuity and resistance. But, since you are getting gas flow when in TIG mode, it sounds like the switch may be working, and there could be an issue with the "Logic P/C Board" p/n 675421. Which, I have no idea how it works, or if it's even available as a replacement. But, if you're in the machine already, you may want to look around inside for any obvious signs of things that don't look right, loose wires especially grounds, loose nuts/bolts, worn wires, dark or burnt looking spots.Good luck.Last edited by redbeerd; 03-27-2018 at 07:50 PM.AHP AlphaTIG-200X Miller Multimatic 215
Reply:Unfortunatey the hf does not work in the start mode either, it will still weld but only with a scratch start.  I decided to dig a bit deeper this evening.  The continous/start/off high frequency switch is physically mounted to the logic board.  Because of that I decided to pull the board for a closer look.  Before I could begin testing the switch I noticed a wire that had burned through its coating and then separated. I replaced the board and jumped the wire but still no hf spark. The burned wire is the green wire that connects one leg of C16 to the ground of the Remote Torch Receptacle (see Figure 5-2) photo attached for reference.  I'm thinking about trying to replace C16 and then going from there unless you think there may be a more likely cause of that wire melting? No obvious signs of C16 (a ceramic cap) failure, I'm just guessing because it's the closest thing in the circuit. Hopefully I'm on the right track! Thanks

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Reply:Forgot to mention, if you try the HF in START mode only, on steel, you'll need to change the polarity selector switch over to DCSP (DC Straight Polarity), which is same as DCEN (DC Electrode Negative).EDIT: I didn't see your post before this was posted.Last edited by redbeerd; 03-27-2018 at 10:13 PM.AHP AlphaTIG-200X Miller Multimatic 215
Reply:

Originally Posted by ryankevans007

Unfortunatey the hf does not work in the start mode either, it will still weld but only with a scratch start.  I decided to dig a bit deeper this evening.  The continous/start/off high frequency switch is physically mounted to the logic board.  Because of that I decided to pull the board for a closer look.  Before I could begin testing the switch I noticed a wire that had burned through its coating and then separated. I replaced the board and jumped the wire but still no hf spark. The burned wire is the green wire that connects one leg of C16 to the ground of the Remote Torch Receptacle (see Figure 5-2) photo attached for reference.  I'm thinking about trying to replace C16 and then going from there unless you think there may be a more likely cause of that wire melting? No obvious signs of C16 (a ceramic cap) failure, I'm just guessing because it's the closest thing in the circuit. Hopefully I'm on the right track! Thanks
Reply:Time for bed now but I did verify the 3 position switch  is working properly so now I think the possibilities are either:1. The logic board is bad (though every component that I could test while it was out at least had some continuity, diodes caps and resistors) 2. A part of the high freq generation circuit itself failed3. Something with C16/The burnt wire situation ...I'll replace c16 next, fix the burnt  wire and go from there. This is getting fun haha but I really hope it is something simple/cheap to fix otherwise I have a really big stick welder in the garage with a water cooler lol. Let me know if anyone has any other thoughts. RyanSent from my SM-G930V using Tapatalk
Reply:Just saw your post thanks I'll go through it tomorrow and report back -RyanSent from my SM-G930V using Tapatalk
Reply:You mentioned the HF circuit itself, did some diagram review and just now noticed the CB (Circuit Breaker, 15A) that's on the back of the machine toward the top. Looks like it's tied into the HF circuit, and even runs through the LOGIC PC BOARD and the HF contacts, which is different than the SG (Spark Gap). That'd be an easy thing to check, and probably should have been the first or second thing to check. The CB is also tied to the 115VAC duplex outlet on the back. So if the breaker was tripped, you wouldn't have power there when the machine was on. Also, I'm seeing some easier ways to check portions. Not plugged in, you could meter (continuity check) the RTR pin C to the LOGIC PC BOARD to make sure all 3 Thermal Switches are in tact. And you could meter RTR pin B to the SCR PC BOARD pin P3-2 (red wire) to check that length. You could probe B and C on RTR and step on the pedal to make sure the pedal switch is working.AHP AlphaTIG-200X Miller Multimatic 215
Reply:When I woke up I saw your post about the circuit breaker being in the loop. The breaker was tripped. I reset and hit the pedal and the hf fired! I just started laughing. Sometimes it is something simple. Hopefully there aren't any other demons that caused the breaker to trip, but right now I'm optimistic.  Thanks so much for your help with this! I have a late night at work today but either late tonight or tomorrow evening I'll put the machine through its paces and confirm everything is  good.  Thanks again!Ryan Sent from my SM-G930V using Tapatalk
Reply:Yup, sometimes it's as simple as the circuit breaker (next to the 115VAC outlet on the back panel that is tied into the HF transformer circuit). Section J in the manual about troubleshooting should have this item listed as the #2. "15A circuit breaker on back panel is tripped. Reset breaker." You may want to actually write that in there. But, at least it got you looking around and thinking about the machine operation. Good find on that RTR ground wire. Hope you get some good years of use out of that machine.
Reply:

Originally Posted by redbeerd

Yup, sometimes it's as simple as the circuit breaker (next to the 115VAC outlet on the back panel that is tied into the HF transformer circuit). Section J in the manual about troubleshooting should have this item listed as the #2. "15A circuit breaker on back panel is tripped. Reset breaker." You may want to actually write that in there. But, at least it got you looking around and thinking about the machine operation. Good find on that RTR ground wire. Hope you get some good years of use out of that machine.
Reply:Good to hear. Hopefully you can get another decade out of it, at least. Yea, it took me a while to learn to look for the (real) simple stuff. But, the more you do it, or don't, the more you'll learn. Either, the easy way or the hard way.AHP AlphaTIG-200X Miller Multimatic 215
Reply:This is great!  I too have an old Linde that was given to me by a friend.  I have done very little tig welding and have limited ideas of how to set up the machine but I did get it running on steel and it worked great to start with until I got the tungsten stuck on the plate I was practicing on.  Since then the hf start would not work, I did same as you with checking the points gap but could never get it to work again.  It has been sitting in my garage for the last two years because I didn't know what else to try.  When I get home tonight first thing I'm going to check is that circuit breaker!!!!  Oh where is it located
Reply:HF system is easy to trouble shoot. Start a logic / control pcb and make sure 115 volts is going in and out with TIG on.Relay on the pcb fails. Then make sure the 115 volts makes it to the HF transformer. With power off make sure you see around 5K ohms on the secondary. Primary is very low. Arc at the points should crackle. not buzz. Open cap will make soft buzz.shorted cap will stop arc. Check the board the points are mounted on and make sure there are no broken solder connections.we use the cap and points from miller to repair these. Make sure pcb is clean so HF can't find a path around the points.Metal dust will cause this real fast.
Reply:Thanks, most of that went over my head but I have a good friend who is an electrician


Reply:If you end up needing parts for this let me know - I have one sitting in the shop that has been collecting dust for the past 4 years. It took a board or two out of it and I couldn't find replacement parts for it plus the cost to fix was to much for what it is worth. You can have what you need if you pay the shipping, sooner or later it will be scrapped out though as I am tired of walking around it.RideKTM350
Reply:

Originally Posted by RideKTM350

If you end up needing parts for this let me know - I have one sitting in the shop that has been collecting dust for the past 4 years. It took a board or two out of it and I couldn't find replacement parts for it plus the cost to fix was to much for what it is worth. You can have what you need if you pay the shipping, sooner or later it will be scrapped out though as I am tired of walking around it.RideKTM350
Reply:My machine must be a bit older than the original thread starters as it looks a bit different.  I don't see a breaker on mine.  There are three fuses under the flap on the front panel and the 15amp one is missing!  I don't know what these are for but I will replace it anyway.  Here are some pics.




Reply:

Originally Posted by ccawgc

HF system is easy to trouble shoot. Start a logic / control pcb and make sure 115 volts is going in and out with TIG on.Relay on the pcb fails. Then make sure the 115 volts makes it to the HF transformer. With power off make sure you see around 5K ohms on the secondary. Primary is very low. Arc at the points should crackle. not buzz. Open cap will make soft buzz.shorted cap will stop arc. Check the board the points are mounted on and make sure there are no broken solder connections.we use the cap and points from miller to repair these. Make sure pcb is clean so HF can't find a path around the points.Metal dust will cause this real fast.