Being curious by nature it wasn't long before I had a look inside. The electronics don't look too bad and the design is pretty basic so anyone with decent electronics knowledge should have a reasonable chance of fixing any faults. The boards are conformal coated to protect them from dust and damp and all plugs and many components are supported with hot glue which is good. One problem I did find is that the bolts on the bus bars between the power boards were not very tight. If left they could cause problems so I tweaked them up.
Like many other cheap Chinese tigs this one is fixed at 60Hz AC so I had a look at the controller board (mounted on the front panel) and found it uses a very simple R-C oscillator circuit to generate the 60Hz. One quick resistor change later and it now runs at 125Hz
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
As the AC balance can handle varing frequency it would also be a simple job to fit a front panel variable resistor to give variable frequency control. Currently I am not to keen on doing this as it would invalidate the warranty. It is unlikely that anyone would spot one component changed on a board but a new knob on the front panel may raise some eyebrows!
Now for my question: what would be the best frequency to use if I have it fixed? I can probably select anything from 10Hz to about 250Hz. I don't know how good the driver circuit for the mosfets on the H-bridge is so I would be cautious about pushing it past 250.
In the future I may investigate making the pulse switchable to a high speed (currently 0.5-20Hz) but I don't know how well the inverter section will handle that.