Repairing a Rotel A14MKII. It was wired for 110v and connected to 230v!

[@electronash]

1:09 - That looks like a 128-pin Xmos chip (XUF208-128-TQ64 or similar), for the USB "DAC" input. The Ethernet and other USB port is more likely handled by the main STM32F207 MCU. (especially since the F207 added Ethernet support, but the smaller F205 doesn't have it.) The Xmos chips are quite powerful for USB 2.0 streaming audio, and DSP etc. They are used a lot in the Audiophile style DACs, for playing back hi-res PCM and DSD music from a PC etc.

[@electronash]

2:51 - They sometimes bolted the smaller transistors (or diodes) to the larger ones, to help with temperature compensation. That can help keep the idle current within a reasonable range, and also help prevent thermal runaway in some designs.

[@MichaelBeeny]

All that digital stuff, fancy display. Looks like more than 50% of the amplifiers has little to do with the actual amplifier. In fact, most of that digital stuff will degrade the actual sound of the amplifier. Remove all that stuff, the amplifier will cost 50% less and probably sound a lot better. It will also be more reliable.

[@campbellmorrison8540]

Typical of consumer electronics, especially amplifiers for some reason, they are a nightmare to work on. You can usually never be able to practically access the unit while its powered on and 9 times out of 10 you cant get any service material, the later is pretty appalling I think, I can sort of forgive the crap construction is the pursuit of cost but they should be sold if you can get at least a circuit. Anyway that's why I don't bother fixing many amplifiers, its very rare to come out with any profit.

[@orangevalleysystems]

Totally agree. I often end up soldering long wires all over the underside / topside of the board to bring all the signals I'm interested in out to a scope or meter for easy access but that might require a major time consuming disassembly. The self tapping screws used everywhere easily wreck the holes in the soft case if you have to keep removing them. I won't normally take anything on that doesn't have a service manual and even if it does I think twice about it. The only way to easily repair something like this Rotel (and others) would be to have a test jig for the boards. There's no way you'd want to have to keep removing the big board to fix something!