Lincoln Idealarc help needed(long post)

Greetings again from the newbie workshop. I purchased a Lincoln Idealarc TIG 300/300(vintage 1984) before the holidays. Came with an LN-7 mig attachment, but no welding cables, interconnect cabling, torch, or foot pedal. For $200, I couldn't pass it up! I've since scrounged all the goodies to make it operational and after some help from the group in a previous post, it seems to be working "ok". The problem I'm having with it is remote control of the welding current. When the switch is up for local control, it seems to be fine although I find the control a little touchy. For example "3" might not produce a good bead and "5" will blow a hole. I'm still chalking this up to technique. When the switch is set to remote, I should be able to control the welder from minimum current to the maximum of what the front panel control is set to. If the front panel is set to "6", the foot control will operate from 0-6. The problem is, it doesn't. The foot pedal will start the welder, but increasing the pedal does nothing. The pedal is homemade, but it has the correct 10k ohm pot in it. Interestingly enough, the LN-7 unit can't control the welding current, either. I dug out the manual for it and started tracing back the circuitry. The front panel control is a 5k ohm pot. That's routed thru the local/remote switch to the power control pc board. I pulled the connector off the board and stuck the ohmmeter into the two terminals coming from the switch. The wire numbers are 208 and 242. As I increase the front panel control, the resistance goes from 5k at "0" to zero ohms at "10". I'll buy that. When I flip the switch to remote and the front panel control is at "0", I read 10k(the value of the pot in the foot pedal). Increasing the foot pedal does nothing because the front panel switch is at "0". Ok, crank up the local control to "10". Now the pedal will swing from 10k to 0 ohms. The only problem is half the pedal travel is used up just to get to 5k. The welder thinks everything is still at "0" because the resistance is 5k or higher. Does that make sense? I have the exact same problem with the LN-7 remote control. I built the pedal myself as well as the interconnect cable to the LN-7, so whatever I did(if it's wrong), it's common to both. Any ideas?

*NOTE: I just checked on the Lincoln website and they show on one of their TIG 300/300 schematics, the remote control pot being 5k. Ok, that explains that, but then why is the LN-7 wrong?? Again, thanks for any advice/info.
Reply to
Jim
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Must be too early in the morning. It's an LN-8, not an LN-7 and the Lincoln schematic shows the pot to be 10k. Maybe this unit didn't originally come with the welder........ Perhaps changing both pots to

5k will solve this set of problems.

-Jim

Reply to
Jim

There are two (maybe more?) different tapers to pots. Linear and audio. Which one are you using? I don't know if this will work here or not, but it makes a big difference in volume. The linear is a straight 1:1 ratio and the audio is exponential. I think this is right, it might be something to consider.

Eide

Reply to
Eide

Jim, I agree with Eide, it sounds like you are using pots that have a logarithmic taper that are intended for audio applications. Try replacing it with a linear pot. Possibly Radio Shack # 271-1715 for 10k,

1714 for 5k, if a half watt unit is sufficient. D.
Reply to
inetcaster

For some reason I missed the original post so I copied it from someone's reply.

I don't agree with the other suggestions that it's a problem with the type of pot you're using. That could certainly cause problems but not the type of problem you described.

Based on your description you do get zero ohms at the control when at one extreme of the pot and if I remember correclty zero ohms should give you the maximum value that you have set on the local pot no matter whether your pot is linear or an audio taper. Zero ohms is zero ohms no matter how you got there. That means that if you press the pedal down all the way you should get whatever you have dialed in on the local control.

It sounds to me like your local pot is dirty/noisy although I'm not sure that would cause the kind of problem you're having. I'd check it with an analog multimeter so you can see how dirty it is. You can't check it with a digital because they update too slow but with analog the needle will jump all over the scale as you turn the knob if it's dirty. Dirt can cause it to open up intermittently and looking at the schematic I see that the remote pot goes through the local one so if the local one did open up you'd get minimum current.

From what you said about the measurements you get at the connector to the control board it doesn't really sound like this is the problem but it's worth checking.

Another thing I'd try is pressing the pedal all the way down and then adjusting the local control on the welder to see if it has any effect on the output current. And in case I'm backward on whether max ohms is minimum output and zero ohms is max I'd try it with the pedal pressed only far enough to get the switch to come on but I'm guessing you've already verified this.

BTW, I used to have an Idealarc TIG 250/250 which has an almost identical remote control circuit and I used a pedal with a 10K pot without any problems. It did call for a 5K but I got a great deal on the pedal with the

10K. The only thing I noticed was that I had to press the pedal halfway down before I started to notice much of a change in output.

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

Reply to
Keith Marshall

Reply to
alphonse

You're correct that the Idealarc TIG 300/300 is AC/DC CC machine but according to the manual on the LN-8 wirefeeder it can be used with a CC power supply. I didn't take the time to read the entire manual but section K3.1.3 is titled "Welding With Constant Current Welding Sources" and tells what to set the controls to for use in CC mode.

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Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

Reply to
Keith Marshall

If you take the time to read the manual, you will find that you can only run SUBMERGED ARC WIRE with the LN* with Constant Current machine. It states in the manual that (In the early years I worked SUB ARC ran on constant current machines Big wires and AC transformers when arc blow on DC was a problem}constant current is only used for subarc welding. YOU MUST HAVE A CONSTANT VOLTAGE MACHINE TO RUN INNERSHIELD AND OTHER OPEN ARC PROCESSES[such as MIG] This take me back to my original post that with TM

Reply to
alphonse

Alphonse, I think you're on to something. A little more digging in the LN-8 manual shows there is an optional variable voltage board that plugs in. It sounds like that's what's required to make the 300/300 work with the LN-8. My limited search so far, tho, has not turned up a Lincoln part number. Thanks for your help. I'll have to limit my welding to stick and tig for the duration and continue to use the Millermatic 35S for mig work. Thanks again.

-Jim

Reply to
Jim

OK, I missed that part.

Best Regards, Keith Marshall snipped-for-privacy@progressivelogic.com

"I'm not grown up enough to be so old!"

Reply to
Keith Marshall

If I located one of these variable voltage boards from Lincoln, would that maybe solve my problem? It'd be nice to have a welder that can essentially "do it all".

-Jim

Reply to
Jim

that maybe solve my problem? It'd be nice to have a welder that can essentially "do it all". If I located one of these variable voltage boards from Lincoln, would

Reply to
Keith Marshall

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