Join Date: Aug 2001
Location: Palo Alto, CA, USA
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I recently purchased a Yamaha RX-V863 and I'm very happy with it so far. Being the curious, technical type, I also bought the service manual for it from Yamaha. It came on a CD and is quite detailed. While it is for the V863, nearly all of it will be the same for the V636. It does answer some questions that people have.
There are two ways to update the firmware -- no news on an actual firmware update being available yet, though. It can be updated via a DVD/CD drive connected to the receiver through an optical or coax digital connection. Or, it can be updated via an RS232 connection. That unusual port to the right of the HDMI ports is for the RS232 connection. A special adapter cable is needed which can be purchased from Yamaha.
The speaker impedance selector (6 ohms / 8 ohms), simply changes the power amp voltage feed from the power transformer to a different set of taps. This lowers the highest voltage that the amps can provide to the speakers and so lowers the maximum available wattage. It affects all of the power amps, not just the front channels. So why does the manual say 4 ohm speakers for the front channels only? My guess is heat, either the transformer itself or the power transistor heatsink or both. Limiting the lower impedance speakers to only one pair reduces the maximum heat that will be generated. But by my reading of the schematic, it doesn't matter which two speakers are 4 ohm. The manual also indicates that if the temperature gets too high, the receiver will change to the lower impedance setting automatically.
The receiver has some self-diagnostic capabilities, but I haven't played with these.
If people have questions that can be answered by checking the schematic, I'll attempt to answer them. Please don't ask me to post the manual as I want to encourage Yamaha to make it available to anyone and so want to respect their copyright. If you have many questions, I recommend you get a copy of the manual yourself.