EEVblog #378 – Dumpster Diving Teardown RepairPosted on October 31st, 2012 6 comments
Repairing a Yamaha Surround Sound Receiver Dave found while Dumpster Diving.
SPOILER: I couldn’t fix it.
Service Manual PDF
Forum Topic HERE
So you wanted Yamaha to save a few bucks by buying cheaper caps?
You do realize all the high-end stuff that the guys actually get the service manual (why do you think it’s online? Yamaha charges $10 for ‘em) and pore through every component choice and examine everything. I’m sure Yamaha and the others could’ve saved a few bucks and bought regular caps, but decided to spend a few extra dollars to ensure the caps are top-notch.
High end audio is very competitive, and even this isn’t “high end audiophile” for its price – but there are many competitors at this price point (probably close to $1000 new) so saving money on cheap caps makes it easier to disregard as uncompetitive.
You should know that there are at least two digital boards – the first one will have the microcontroller that controls power (PS – you could’ve used the remote control) and all the various switches and audio paths to route audio and video this way and that and control the display.
The other digital board has the DSP used to decode the DOlby Digital and DTS compressed audio, as well as do various effects.
The bottom board is the power amp board – it’s attached to the heatsink and has the finals.
The upper boar you removed was the microcontroller digital board – the one where all the signals are switched back and forth (the vertical boards handle hte signal and contain the switches to route audio to the bottom board).
David is quite right about those caps. As he said, Nichicon brand caps are top notch and you can’t fault them for using those. But using “audio grade” capacitors in the power supply isn’t going to make any difference to the sound quality, which at ~0.05% THD+N isn’t all that great anyway. In fact, in a well-designed amplifier, none of the electrolytics are critical to performance as long as they don’t fail horribly.
I could go down to Jaycar, pick up a bunch of parts, solder them to a protoboard and make an amplifier module that can deliver 100W at <0.001% and that's without necessarily using fancy output transistors. With fancy transistors you can get 0.0004% or better. That's less than 1/100th of the rated distortion of most of these Yamaha (or similar brand) ~100W surround sound receivers.
The power supply filter caps have little to do with distortion performance. As long as they don't have such high ESR or low capacitance as to cause the supply rails to sag excessively under load then they're doing their job. A well-designed amplifier will have a power supply rejection ratio sufficient that the typical ~20V of ripple you get from the supply under full load does not get into the output in any detectable manner.
The components which DO affect sound quality are the output transistors, resistors and capacitors in the feedback network, small signal transistors in the front end and the output filter (typically LC). If they are indeed using MOSFETs as output devices then they're never going to get very low distortion and so using "audio" caps is pointless. Even if they're using bipolar transistors, with such a packed chassis with a large non-toroidal mains transformer radiating hum into everything and long, convoluted signal paths it's no wonder that the result isn't quite "audiophile" quality (a term which I think has been seriously damaged by the volume of bogus gear and concepts now attached to it).
Probably got zapped in a recent thunderstorm. Micro may well be dead.
Dave, I guess the ” heatsinks” pads on the smd component are just solder traps for wave soldering.
Can it be your office neighbours devised their own obscure way to send you stuff for teardown? They just put a gadget into dump-room at night and then run to their monitors to watch youtube in the morning???
Leave a reply