I picked up a Lincoln tig 300 square wave machine a couple weeks ago.
The guy claimed that the power couldnt be dialed down to anything less than about 150 amps. Ive receipts for a number of boards he purchased in '00 etc etc, with no fix.
So I powered it up today to diagnose what is really going on.
- It will not dial down to less than about 111 amps,using either the pedal, or the main amp control pot. The machine has digital display for volts and amps, and with the main control all the way down, I get an E11, and turn it a smidge, shows 111, then as the knob is turned, goes all the way to 375 amps as one would expect Hooking a stinger up, yes...it really is about 111 amps at low, and all the way up blew an 80 amp breaker on my sub, so yes, that portion is accurate.
There is no Hi/Low range switch on the machine.
No output on AC. Tiny spark, but no real welding current, using local, or remote with a known good pedal. Pedal does kick the contactor, and does vari welding current, but wont bring it down below that 111 volts.
No HF in any configuration. This COULD be dirty points, as its not been used for at least 8 yrs, but thats not a big issue at the moment.
First thing Ill do is check the main amps control pot, to make sure its in spec and both sides have the prope variable resistance.
I do have the schematics and drawings, but was looking for some input on how things actually work..IE..when the main amp knob is turned, how is it actually controlling the output of the transformer?
With a minimum current of 111 amps, something is not going low enough, or high enough to vari current to lower values.
Why would it not have output on AC but does on DC? Thats a bit odd.... Ill clean the AC/DC+/DC- selector switch of course. It IS a square wave machine, so whatever converts the AC sine to square wave sine may be an issue. I think thats some sort of chopper circuit?
Anyone have any ideas or where to start looking? This is a weird one.
The FF designation at the end of the code number means "full function"..whatever the hell that means. I assume its the timer circuits for post and pre flow, crater, spot etc ?
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