EEVBlog #379 - Yamaha RX-V557 Receiver Fix

[Salas]

LOL. He looks like Michael Stipe on steroids rather.

[MysteryBunny]

You know this is strange, when your electronics blog gets so big it crowd sources itself to fix your problem even before you have the thing apart...Then it criticises you for not accepting that it just did that!!! I was laughing at all the comments on this video with the people complaining that they fixed it...

People went out of there way to do that, and then DAVE just crashes their party with pure theory and his thinking process on the table...Ridiculously good entertainment!

Most people are not willing to show their mistakes. If people can't see a mistake, you can't make a decision. You're lost...Experience is only gained by mistakes...

Whenever I make a mistake, it's intentional and it's based of thousands of decisions and guesswork.

I don't think you can trademark a particular process unless like he says, you are a specialist on the manufacturer...It would absolutely fail in other fields.

I love the flow of this, the education format is based on making correct techniques yourself. I can google answers for a lot of things too, but at the end of the day he's really saying you'd never learn how to fix something...Interesting to see everyone contrast!

I think it's interesting too to see the people who want to see the methods he would use on that design, and then see the people who casually passed by to comment with no pre-requisite knowledge...Then there were others who followed the blog regularly...It was like 3 groups, except the biggest group was all the new people who appeared so ANXIOUS to get in on the action!

I often watch Dave's blog so I can see equipment and follow the format. There's a point where you can express every emotion you have through your hardware. It's difficult for outsiders to interpret that as rational because of the social norms involved.

[tom66]

After seeing this blog, I picked up an RX-V450 from eBay for £20. It has the exact same fault, and probably the exact same capacitor has failed.
http://www.badcaps.net/forum/showthread.php?p=283827

[king.oslo]

In this video, Dave explains that one should use an isolation transformer. Have I understood that by isolation, I no longer get shocked by touching live and ground simultaneously? I will only get shocked if I touch both conductors?

Is this correct?

Thanks.M

[T4P]

I think what he said was between the scope and the DUT not your safety sake, you can still die from a isolation transformer

[Bloch]

I can definitely count an aussie among my favorites, but she's aged a lot better than the blokes.

Frankly, no one can beat ACDC they ROCK





But i will agree that the aussie can make great music

[poptones]

[king.oslo]

I think what he said was between the scope and the DUT not your safety sake, you can still die from a isolation transformer

I am not asking about dying (although I do not want to die either) However, what is the logic of an isolation transformer if it is not to isolate yourself from ground referenced power supply?

If oscilloscope cannot get shocked between mains and ground, I suppose I cannot got shocked between mains and ground if using an isolation transformer?

Thanks.

Marius

[Dataforensics]

Small update regarding these Yamaha AV ranges.
I have had an RX-V459 for around five years and although working, the display is suffering from VFD fading and is very hard to read.

After seeing Dave's repair of the 557 I bought a broken 459 off Ebay for a tenner. Seller stated it had suddenly failed to turn on. So I thought if too hard to fix, then whip out the display and change for my working model.

Anyway, looks like same/very similar psu/operation board as 557, if a bit harder to get at and different Yamaha part number, still a 22nF630V. The one in the broken unit reads 4nF. Replaced it and previously broken 459 powered on fine.

So as a test I checked the same capacitor in my old working 459, and it reads 7nF, so it looks like the capacitance can go pretty low before the unit fails to turn on.

Only down side is that I was building myself up to buying one of Yamaha's new RX-V673's with HDMI switching/networking and now much of the excuse has gone. Still probably cheaper after Xmas.

Tony
 

[ceteras]

In the EEVBlog #379 - "Yamaha RX-V557 Receiver Fix", I think I've spotted a small misunderstanding there.
Nothing big, but I want to write it here so other could confirm, maybe (?).

At 08:45, Dave follows the mains from the power connector through the transformer and so on, then finds that the return is AC coupled through C409.
This is where I disagree, and below is how I see it.

The mains goes through the transformer's primary then, when Q404 is switched ON:
- one alternation through the D408 rectifier bridge  top-right diode, then Q404, then the bottom-left diode in the diode bridge
- the opposite alternation goes through the top-left diode, then Q404, then the bottom-right diode
Notice how Q404 gets a rectified current (so its DS voltage is always positive and current flows through it in only one direction), but Q404 together with the D408 bridge are controlling an AC voltage applied to T401's primary winding.
When Q404 is OFF, all diodes will be off because they will be connected in two paralleled "reverse-series" groups.

So the mains return is not AC coupled through C409, but it goes through the primary, then the bridge+q404 together from right to left, then back to the mains.
I don't wanna be a wise-guy here at my first post (or am I?), but I've learned so much from Dave's videos and this is my 2 cents I can give back!

Pardon my English if it doesn't make sense, and forgive me if this is discussed elsewhere (that wouldn't make sense to me).

Keep it up!

[Fezder]

Nice video, again learned something from Daves videos. . and with such language that is not cryptic english ....

[iXod]

Have a Yamaha RX-V992 with same problem: push the power button, get a "click" and just a flash of the power LED (located in the volume knob).

But the "sub power supply" PCB is different than the 557 model: doesn't use a dropping cap, but a small 12v transformer instead to generate the "always on" control voltage. The output of the sub PS board is around 14.2 vdc, very little ripple (0.05v).

There is a "pink cap" in there (used as a filter in the transformer 12v secondary) and I replaced it (the old one measures OK). No change in symptom.

I'm trying to grok the schematic and figure out what might be the cause:

http://elektrotanya.com/yamaha_rx-v992_sm.pdf/download.html

I jumpered the mains relay contacts which powers the main transformer -- still no change in symptoms.

I used a Variac to run up the mains voltage. The main transformer secondary consists of 4 center-tapped windings. Voltage measurements are consistent: each winding increases linearly with mains increase, and both halves of each winding increase equal equally.

I ohmed the output devices and no shorts found. So I've ruled out a shorted power device.

Still have yet to check DC voltages.

Is there error signals that I can check first to tell me whether it's missing voltage or some other test that's not passing? What does the uP look for and where are inputs are these located?

Any suggestions welcome.

Thanks!

[DimBulb]

I knew I tossed my RX-V1700 too soon. Watching Dave (and community) fix this one made me wish I had that thing to prod around in.

Live and learn.

Thanks Dave for another entertaining video.

[iXod]

Dave.

4:30 -- C405 isn't a filter cap, it's a "wattless" dropping cap. Acts like a high value resistor (without the P dissipation). When bad, probably acts like a VERY high value resistor.

Have my own Yammy I'm working on (RX-V992) with same symptom, different circuit. (See my post in this thread 3 days ago...)

[batou]

Is there a permanent fix for this? I assume the replacement cap will die at some point

[tandoorlee]

Just wanted to say thanks, this fix cost me 50 cents !
Why did the cap fail, we were away for a weekend, the amp was left on, many thunderstorms....