LABOR MMA-160 inverter welding machine gives very low output voltage. Which electronic components should I control? Which electronic components should I replace most likely?
I believe that this is a photo of the machine:
It looks like a generic imported inverter, similar to the famous ZX7-200.
Is the machine still under warranty? If so, contact your supplier or the manufacturer and ask for a replacement unit. Defective inverter welders are not easy to fix, a DIY-solution is not likely. They are complex machines, crammed with a lot of electronics in a small area. With no documentation, they are difficult to troubleshoot.
To investigate the fault yourself:
- disconnect the machine from the AC supply, wait an hour or two for the capacitors ( with up to 325v DC !! ) to safely discharge, then remove the covers and check for:
- loose push-on spade tags at the back of the main power switch and on the bridge rectifier ( probably a rectangular alloy block mounted on a heatsink, with 4 tags, - there may be two rectifiers in parallel )
- loose bolted connections on heavy internal cables and copper or aluminium busbars, at heatsinks, and on thick tracks on the PCBs, and at the back of the front panel sockets.
- any loose or poorly-seated plugs on multi-wire harnesses between the PCBs
- any sign of blackened or burnt components. This applies particularly to the power transistors ( MOSFETs or IGBTs ) and diodes that are bolted or clipped to the finned aluminium heatsinks. You may find scorched tracks on the circuit board in those areas, or melted legs, or cracked/burst components.
** Please be aware that dangerous high voltages are present in inverter welders. DC is more dangerous than AC. Voltages may be present across charged capacitors even after the machine has been powered off and disconnected from the AC supply. Do not work on this machine in a live condition unless you are confident and have the correct equipment.**
Tracing the mains input wires will lead you to the bridge rectifier(s), possibly via a filter circuit. There may be a soft-start circuit ( bypassed by a relay after a delay to allow the large electrolytic capacitors to charge ). There should be about 325v DC across the smoothing capacitors, and this feeds the inverter section, where the multiple MOSFET or IGBT power transistors turn it to high frequency AC. If you are able to do this safely, you can check the 325v DC.
A low output voltage could be caused by one or more open-circuit power transistors, or a failure of the PWM pulse driver circuits for their gates.
If you locate faulty ( short- or open-circuit ) power transistors, it is important to note that the gate driver circuits may have suffered consequential damage, so it is vital to verify them before fitting new transistors. This type of issue is discussed here:
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