EEVBlog #379 - Yamaha RX-V557 Receiver Fix

[EEVblog]

Dave.

[NiHaoMike]

Is there a patent on that circuit? If so, reading it would be the best way to understand how it works.

Maybe saw that bad cap in half to see how it might have failed. It looks like the manufacturing is defective and one of the terminals detaches internally.

[Pentium100]

I was fixing a dehumidifier that would cycle its power for some time until it warmed up and worked normally when I encountered a bad film cap for the first time. The 1uF cap had either reduced capacity or increased ESR, but the result was that when the MCU switched on the relay (for the compressor), the voltage would dip and the MCU would reset. The capacitor was used in a CR dropper to provide 5V without the use of a transformer.

[firewalker]

OFF TOPIC.

Can someone put an LCR to an oscilloscope an post the waveform? Is it sine?

Alexander.

[David_AVD]

The capacitor was used in a CR dropper to provide 5V without the use of a transformer.

There's quite a bit of gear that uses a capacitor fed supply like that.  Pump controllers, vacuum cleaners, etc.  It's also the first thing to check (for low capacitance) when servicing these items.  They usually drop capacitance slowly until the circuit no longer operated correctly.

[nitro2k01]

Hmmm, 5.5 V from regulator minus nominal 0.7 V diode = ~4.8 V?

8:24, no that's actually a Zener that you're pointing at. It's a 10V Zener that's clamping the voltage for the half cycle when a positive voltage is presented over the didoe. Then that is filtered through D406 and C406 which then goes to Vdd for the rest of the circuit.

A Zener will typically have the brackets pointing counter clockwise, like a Z, whereas a Schottky will typically have them pointed clockwise like an S, and also have another little line segment.


Oh and btw...

[Sionyn]

ah come on dave ACDC would've been better

[Rutger]

No way Man at Work it 10x times better, I love that band from Down Under.

[Skippy]

Where did you get the schematic from (did you say during the video?)

[Sionyn]

id like to see dave do a angus young

[Rutger]

Wondering were this was filmed? Looks very dry, but you have a power lines in the background.

[Baliszoft]

How about this?
Family Guy land Down Under

[Dread]

Doing repair work for years I know how Dave feels when people point out "Ohh it's that part that’s bad". I had a guy in our company that seemed to have a photographic memory when it came to remembering boards he had been through already and he did that all the time.

My only comment to Dave would be that he broke one of the main rules of Repair and therefore paid the price.
"Never Ignore a voltage reading that is unexpected, always back track the problem and fix it first!"
Had Dave not ignored those oscillating reading after the bridge Rectifier and just stepped back to see where they came from he would have seen the problem in less than 10 minutes.  Of course that's easy for me to say when working at a bench with no camera rolling so in a way I do understand why he moved on to other areas.

[PA0PBZ]

Had Dave not ignored those oscillating reading after the bridge Rectifier and just stepped back to see where they came from he would have seen the problem in less than 10 minutes.  Of course that's easy for me to say when working at a bench with no camera rolling so in a way I do understand why he moved on to other areas.

Those readings are supposed to be that way, I think you missed what the circuit does.

[zaoka]

DAVE Please!

Dont? stop now when its most interesting!!

I think that 10.2V on secundary is droping down at the moment you turn on the receiver.

Please install old cap back and use MinMax(Peak) feature on Fluke and monitor 10.2V to see if it changes when you press power button.

Its either going low or going high and IC403 (overvoltage protection) kicks in.

Also measure the voltage across C406 at the moment you press power button.

This is great opportunity to use scope on secundary to see how low and how long voltage going down at the moment you? turn the unit on and than use MinMax feature of Agilent, Fluke and GM meter to see if they all can catch that!

Also we all have Fluke meters and would like to see more GM meter or Agilent in action

Please dont give up now!! )

[Monkeh]

Also we all have Fluke meters and would like to see more GM meter or Agilent in action

 

[Pentium100]

The secondary voltage may be OK, but most likely what happened was that the voltage for the 4013 chip was too low (it is supposed to be around 8V, but the chip can work down to 5V or a bit less IIRC), IC401 remained off (because it has 6.8V zener in series), PDET (power detect) signal remained low so the MCU went into protection mode and did not turn on.

Interesting thing here is that the 5V regulator is on a different board. This standby power supply supplied 10.3V to it and gets back 5V.

[LEECH666]

Hmmm, 5.5 V from regulator minus nominal 0.7 V diode = ~4.8 V?

8:24, no that's actually a Zener that you're pointing at. It's a 10V Zener that's clamping the voltage for the half cycle when a positive voltage is presented over the didoe. Then that is filtered through D406 and C406 which then goes to Vdd for the rest of the circuit.

A Zener will typically have the brackets pointing counter clockwise, like a Z, whereas a Schottky will typically have them pointed clockwise like an S, and also have another little line segment.


Oh and btw...

Trollcap strikes again. Made me chuckle. xD

[LaurenceW]

Dave, is that the only sound you can get out of the Yammy? If so, I fear she's still skewered, mate.  Can you check if you've accidentally pressed any "Lo_Quality" button on the front?

[EEVblog]

Dave, is that the only sound you can get out of the Yammy? If so, I fear she's still skewered, mate.  Can you check if you've accidentally pressed any "Lo_Quality" button on the front?

Assuming that wasn't sarcasm 
The lapel mic was very close to the woofer, so you'd get huge low end domination from that placement, giving it that "low-fi" effect.
It sounds just fine in real life.

Dave.

[poptones]

As good as men at work can sound I suppose. Seems to me you went an awful long way to such a short destination.

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

[Salas]

Nick Cave is an Aussie performer/songwriter who has some musical depth and deserves to be mentioned also, although Minogue has a certain "back"ground. They had done Where The Wild Roses Grow duet though which was a spooky but fine antipodean coalition IMO. She is just 43 or 44, the Men At Work blokes must be in their 60s now. The frontman was Scottish BTW although he had turned Vegemite to the bone after he had moved to Australia.

[poptones]

I didn't know nick cave was aussie, I thought he was part of that london scene. Interesting.

Another of my favorites was Midnight Oil. I had at least three of their albums, I used to like listening to Red Sails in the Sunset because it had "Kosciusko" on it and I lived near Kosciusko (MS, not oz).

[Salas]

Yeah, Cave had this divided Berlin squatter wasted outlook and that Blixa mate from Einstürzende Neubauten, so he could be easily passed for underground European roots, or as Londoner bcs he formed The Bad Seeds there, but he is very much an Aussie, his first moderately known outside Oz band The Birthday Party was formed in Australia.  The Oils's vocalist turned to a politician. INXS was another Oz world export, and the super rich and famous Mancunian Bee Gees started their music making as relocated kids in Australia, made hits and returned to England to push their career, as they actually succeeded. 

[poptones]

Oil's vocalist turned to a politician? You mean someone would vote for a guy who likes like the bad guy from "The Hills Have Eyes?"

[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....