Welding Tips and Tricks

I have a Super 200p and have been very happy with it until now.
I was going to do some MMA welding and discovered that i had no arc!
I double checked all cables, ground but they were good.
Then i tried plasma and TIG ,both AC and DC, same result, no spark at all.
The display reads "000" no matter how i turn the "amp knob".
The "over current light" does Not come on
I hear relays click as i switch from MMA to TIG, sounds normal
I have measured all power transistors and diodes and i cannot find any shorted component.
On the "top left" circuit board i measure 320 volt DC in from the rectifiers below but there is 0 volt out from this board.
I beleive the "front board" (the one with the potentionmeters) send controll voltages to the "top left" board to regulate current and so on but i cannot find any regulated voltage when i turn the "amp knob" and measure with a multimeter
There are 2 green LED's on the "top left" power board, they are lit up, (i think they indicate the 320 volt DC)
There are 3 red LED's on this board (and an small adjacent board thats soldered to this top board) none of these LED's are lit up.
there is a board "in the center at the bottom of the machine" this board gets 4 volatages from the transformer also down at the bottom.
the transformer puts out 4 20 volts in 8 cables that feed this board, there are 3 15volt voltage stabilisers on this board, they all have 15 volt out, but there are 4 connectors leaving this board, 2 wires each (red and black) leeding up to the different power transistor boards, there is only 4.5 volts at these connectors.
I am a trained electronics repairman (or used to be, i dont work with it anymore) so i should be able to repair this if i only had a schematic or got some tips on what to check next.
I will ofcourse pay for a schematic if anyone has it.
So anyone who had this problem or Everlast support, please post some info about it
Regards /Janne Strom

Janne, I'm not affiliated with Everlast, but I will help where I can.

I found this pdf online. I'm not sure if this is the machine that you have or not? http://www.everlastgenerators.com/downl ... ter1.2.pdf

Do you have access to an oscilloscope? Can you check the MOSFETs at the final stage? If you have a scope, can you check to see if the PWM signal is reaching the MOSFETs?

If you know how to use a HUNTRON TRACKER, it can speed up the troubleshooting process as it allows you to test components in circuit with the power removed. It produces a visual cue for component signature analysis. This is very useful when trying to locate a faulty component that physically looks fine. http://sound.westhost.com/project119.htm

When troubleshooting circuits, I sometimes use unconventional methods. For instance, I use a non-contact thermometer to look for hot spots. An overheated component usually means that there is more current flowing thru it, than it was designed to handle. http://www.electromannsa.co.za/shop/?q=node/340

Also, when following a circuit without schematics, I draw different colors on the circuit board traces with MARS fine tipped permanent markers. (don't worry, rubbing alcohol or a similar product will remove the marker when you are done troubleshooting.) I try to follow the flow of the circuit. The permanent marker drawings help me to visualize the different voltage rails and return ground paths on the board. They also show me what I have tested and what is not yet tested.

If you read the same voltage on both sides of a resistor, chances are pretty good that the resistor is either shorted or of a very low resistance value or the circuit has no return path. Just because you see a voltage, it does not mean that there is current flowing. Some people miss this simple troubleshooting tip. If you had a string of resistors and measured the same voltage between them all, one could only conclude that there was no current flowing thru these devices as each device should produce a voltage drop. Usually, you will find that there is an open circuit somewhere, sometimes it is a hairline crack in the circuit trace of the board.

I always write down everything that I do when troubleshooting. (like a lab report) This has often helped me find the problem, by reviewing what I know about the circuit and what I don't know about the circuit. I also write down any questions that I have about the circuit, like what does that LED indicate?

There are a few other pieces of test equipment that I find useful.
A ring tester, for checking out coils and transformers.
http://www.electronicrepairguide.com/bl ... esult.html
An ESR meter for checking internally shorting capacitors and low value resistors.
http://www.capacitorlab.com/anatek-blue ... /index.htm
I also use my nose. I smell the circuit boards to see if something smells burnt. Re-seat all connections and clean them if they look suspect.
In my opinion, the best contact cleaner in the industry is Cramolin but it has changed names to DeOxit because of some chemical that was removed due to health concerns. http://store.caig.com/s.nl/sc.2/category.188/.f

Most important of all, make a plan. If you don't have schematics, don't fret. Take a piece of paper and draw out a block diagram of what you do know. What are the main boards, what are the connector numbers, what do these connectors connect to, draw it all out on a piece of paper and stand back to have a close look at the unit as a whole. By slowly identifying each component and what it does for a living, you can slowly zoom in, on where the problem is hiding.

The biggest weakness I've encountered with Chinese electronics is "cold solder joints".

They're about productivity to the point they work the wave-solder machines at the edge of their capacity, and sometimes the heat-soak isn't long enough.

On the high-voltage circuits, I'd look for discoloration in the green dye of the board around solder points. If Werkspace is on the right track with the MOSFET signalling, you might be tracing to find a cold-solder joint (IF that's the problem).

As if it weren't complicated enough...

Steve S

In the last picture, I see four ceramic resistors of at least 1W that appear to have thermistors in series. Have you checked these for continuity? I'm probably stating the obvious.