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The Yamaha AV receiver - trials and tribulations with a soldering iron
#1
bit of a long one here, so just writing this for my own memory

Wife wanted ot play some old LP's. I didnt have an amp, speakers, or a record player.

Found some nice wharfedale speakers on gumtree two blocks from my house, contacted seller, we made a deal, I went to pick them up, got taking, told him I still needed an amp and a record player, so he said he had an amp for £50, do I want it? sure.

Put it in the boot and drove home, pondering why it was under his bed to begin with, pondering if he ever said "do you want a *working* amp?"

needless to say, plugged it in and it powered up, then powered down. Google, I bessech you..find me a solution. Most of google is awash with a capacitor fix that applies to most yamaha amp of the early noughties vintage. its a 22nf ~600v item, so I bought a few on ebay, but didnt think it would fix it..my amp did turn on, it just didnt stay on, so the +5v standby voltage is probably there (which this capacitor fix is for).

capacitors came, I soldered one in, Still the same. OK, not the end of the world...the main possible culprit is eliminated, so the rest should eb to spec...so if I multimeter the thing, it should all be ok, except for the faulty bit. logically speaking *cough'''cough*

a nice thing about these receivers is that there are loads fo test points ont he boards, and nicely labelled. I had +33v, I had -33v, I had +12v and -12v, but I didnt have 5v and -5v.

So took a good look and found the voltage regulators. There's no -5v regulator, and the service manual doesnt mention -5v..so lets just assume that is the way it is, and go after +5v. The regulator is there...+12v input is good, grnd is good, 5v output is kaput. Yay, we found the fault.

and cool, its a LM7805, the most common one you can find (well, pretty much). New ones arrived yesterday and soldered them in, amp all working today and pretty charmed about it.

Things I have learned
1) its quite possible the seller sold me an amp that was working, but if it sits about it get grumpy and things stop working. The web is littered with tales like these.
2) if your yamaha receiver is *dead*, suspect capacitr c405, 22nf ~600v. Piss easy to replace
3) if it powers up then powers down, its normally detected a fault on the output...or in my case, no power to the cpu.
3a) there's a button sequence to power it up into a failsafe-type mode, and diagnostics will come up on the screen. Option 9 shows you the voltages as some sort of scale...you need above 36 for a good 5 rail. Also, fault codes are stored, so you need to clear them before it will power up properly, even if you have fixed the reason for the fault code (kinda like an airbag light)
3b) ti: boot fail: means it didnt boot form the cpu side of the world, which is a big big clue your 5v rail is dead as that is pretty much what the cpu runs off
4) the insides of these things are really friendly to service tech. Everything is labelled nicely, with tie-downs for the wires, boards come out fairly easily..this isnt "alba" or "hibatchi"..its proper good stuff

Now to get me a record player.
Box, check...juice, check...new battery, check.....SQUONK! Big Grin
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