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
I am almost sure that the TM 300/300 Lincoln's are all AC/DC CONSTANT CURRENT power sources, which is fine for STICK AND TIG welding. However, you must have a CONSTANT VOLTAGE power source for Mig or any other wire welding. That is why the LN8 wire is not responding...and does not belong hooked up to the welder you bought. .If your welder says CONSTANT CURRENT and CONSTANT VOLTAGE [CC/CV] your problems are elsewhere.
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 300/300 AC DC CC he CAN NOT do MIG welding with this set up.
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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