The next step on our tour is the controller board. The controller board is mounted in the top of the device, and connected to the power stage board by the ribbon cable we unplugged a little while ago. By removing a couple short screws, we can release the controller board from it’s flex-button prison and take a look.
Umm, buttons, 7-segments, discrete logic – not too exciting. That 20-DIP with the sticker on top is a micro that runs the show. It’s a Samsung S3F9454BZZ and from what we can tell, it’s notoriously hard to hack. So no firmware mods this time folks, this is strictly a strip show. Micro takes timing data (we speculate) from the current transformer and delivers pulses to drive the gates of the IGBTs. Get your timing right and you drive the tank into resonance with tasty results. Get your timing wrong and you try to switch 500V with 20A running in your IGBT and the 10kW transition loss blows your switch with very un-tasty results. So the controller is important, just not that interesting from a hacker sense.
Fig 9 – The Controller Board
Back to the mainboard. Back to the back of the mainboard, to be precise. In order to take a peek at those power components, we’re going to have to get the heatsink off. We can guess at their function, and we can see the IBGT markings straight away, but to be sure we’ll have to get the heatsink off. The only problem is: one of the components was screwed into the heatsink and THEN the components were soldered in! Now the screw is trapped!
Fig 10 – Back of the Power Stage PCB
If you search long enough you may find the missing hole that allows you to unscrew the heatsink without desoldering. In our board we just had to drill down into the PCB a bit and presto! The missing hole appeared.
Fig 11 – The Missing Hole