In my frustration about some lost footage I took an APC Smart-UPS 750 to pieces. And while I was at it I took a closer look at the mains AC side with all the relays and the transformer (a combined autotransformer/transformer) to find out how it works. At the end I’m zooming in on the controlling section of the main board and go over all the chips (all types with their function in the video).

00:00 Removing the front plate and opening the battery compartment – there’s the first chip
04:20 Opening the case – the easiest part
07:23 Getting the mainboard out – it won’t come easy
12:41 Mapping out the connections to the main board – wiring diagram
19:31 Probing the mains AC connections on the main board – unsuccessfully
22:10 Looking at the components on the mains AC side – big and chunky
24:24 Analyzing the transformer – diagram of its windings (autotransformer)
34:45 Analyzing the relay switching of the transformer – circuit diagram and principle of operation
45:17 Analyzing the mains input/output side – filters, power factor correction and measurement including circuit diagram
49:36 Analyzing the low voltage power section – buffer capacitor and H-bridge including circuit diagram
53:04 Looking at the controller section – a whole lot of chips and their functions

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