Author Topic: EEVblog #378 - Dumpster Diving Teardown Repair  (Read 23328 times)

0 Members and 1 Guest are viewing this topic.

Online free_electron

  • Super Contributor
  • ***
  • Posts: 7035
  • Country: us
    • SiliconValleyGarage
EEVblog #378 - Dumpster Diving Teardown Repair
« on: October 31, 2012, 06:01:11 am »
Heatsink tabs ? Those are 'solder thiefs' !

these boards are wave soldered. so they position the tqfp packages under a 45 degree angle in respect to the wave. this causes the solder to jump from pad to pad and the surface tension avoids the shorts. you do need a run-in for the wave so you will find small thief area's on 3 corners. the last corner ( where the wave exits ) has a longer 'thief area' to make sure there is no short remaining between the last few pins as the wave exits. so the board goes through the wave with the short thief area first and exists the wave witht the long thief area.

there is an official IPc standard to design these thieving area's.  the shape is differen for two row as opposed to quad packs.
« Last Edit: October 31, 2012, 06:04:12 am by free_electron »
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline Alana

  • Frequent Contributor
  • **
  • Posts: 296
  • Country: pl
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #1 on: October 31, 2012, 07:02:38 am »
At least i know that I'm not a complete moron. I had one of similar HIFI sets to fix with very same problem. Result: i told the owner that it seems like main uP is gone. I wonder if Dave fixes it, and if i can find my mistake from before 2 years [if there was any] :D
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #2 on: October 31, 2012, 07:03:22 am »
I have a suspicion that's not a switching supply... it looks like the transformer is straight across the mains.
 

Online PA0PBZ

  • Super Contributor
  • ***
  • Posts: 3877
  • Country: nl
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #3 on: October 31, 2012, 07:43:52 am »
I have a suspicion that's not a switching supply... it looks like the transformer is straight across the mains.
It is, did you see the clever way they switch the power to the transformer with the bridge and the fet?
Now I also understand why there was no cap behind the bridge.
Keyboard error: Press F1 to continue.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #4 on: October 31, 2012, 07:57:11 am »
Yeah, I'm thinking that the reason it's pulsing is they are pulsing the power to the transformer.

That way they can get low standby power (sub 1W) without using a real switching supply which potentially introduces noise (in a good system, e.g. a scope, it -won't-, but the audiophiles would get annoyed otherwise.)
 

Offline Rutger

  • Regular Contributor
  • *
  • Posts: 201
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #5 on: October 31, 2012, 08:14:08 am »
How about unplugging the power to the amplifier board and eliminating at least a possible bad output mosfet.
 

Offline ecat

  • Frequent Contributor
  • **
  • Posts: 296
  • Country: gb
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #6 on: October 31, 2012, 08:26:56 am »
I fixed a similar Yamaha with a similar turn on problem a few years ago.

Each of the power amps has a protection circuit on the output which combine to drive an 'all is good' relay. When a fault is detected on any of the channels, eg blown output transistor, the relay drops out and the amp appears dead as a dodo. Time to remove the upper board behind the heatsink and get down to some serious audio amp debugging :)

... or do what I did, remove the upper board and start clipping the leads to the output transistors until the problem goes away. I ended up with a nice 6 channel amp instead of a 7 channel, by hay, it was a super cheap fix.

How about unplugging the power to the amplifier board and eliminating at least a possible bad output mosfet.

iirc this doesn't help. No power to the amp boards equals no power to the safety relay so the amp still appears dead.



« Last Edit: October 31, 2012, 08:31:34 am by ecat »
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #7 on: October 31, 2012, 08:36:35 am »
That was interesting. Maybe the processor checks the output transistors or something and does not start up because it finds a fault?

The yellow wires from the transformer are likely for the filament of the VFD.

Seeing this video made me appreciate my Denon amp even more - in the case that the microcontroller fails I could replace it with a small set of 74HC or 4000 series chips, I would lose the remote control possiblity, but I do not have the remote anyway, so not a big problem (other than the remote, the MCU just switches on the appropriate relays when a button is pushed to select input etc).

tom66 - in a (modern) scope the analog parts are small and can be shielded relatively cheap. The analog part in an audio amp is usually quite big, so you would have to place all those boards in a can.  Besides, scopes usually have 8 bit ADCs, so about 48dB of SNR anyway, compared to 110dB (line inputs) of an audio amp. If the amp has a phono input then the requirements are even higher, since a cartridge outputs only 0.5mV (MC) to 5mV (MM) and my amp has 94dB SNR for the MM input.

PA0PBZ - a very similar circuit is used in a couple of my tape decks to control the speed of the AC reel motors (but with a bipolar transistor and in linear mode).
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #8 on: October 31, 2012, 08:37:52 am »
Wouldn't such an amp click once so the trafo gets power and then can test the outputs? Or does it do it in standby somehow?
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #9 on: October 31, 2012, 08:40:16 am »
Wouldn't such an amp click once so the trafo gets power and then can test the outputs? Or does it do it in standby somehow?

Quote
tom66 - in a (modern) scope the analog parts are small and can be shielded relatively cheap. The analog part in an audio amp is usually quite big, so you would have to place all those boards in a can.  Besides, scopes usually have 8 bit ADCs, so about 48dB of SNR anyway, compared to 110dB (line inputs) of an audio amp. If the amp has a phono input then the requirements are even higher, since a cartridge outputs only 0.5mV (MC) to 5mV (MM) and my amp has 94dB SNR for the MM input.

Interesting. It might end up being cheaper for low power analog stuff like this, it is consumer electronics after all...

The new Rigol DS2000 has some 400µV noise floor with a heavily shieled PSU but the older DS1000E still manages around 1mV without (much) shielding.

I noticed some jamicons on the logic board, but they aren't too bad for general purpose caps.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #10 on: October 31, 2012, 09:07:08 am »
The new Rigol DS2000 has some 400µV noise floor with a heavily shieled PSU but the older DS1000E still manages around 1mV without (much) shielding.
The Rigol has a heavily shielded PSU and shielded analog sections (which most likely include opamps or other devices to amplify the signal (because I doubt that the ADC has 400uV noise floor). Still, those sections are rather small, compared to low power analog sections in an audio amp (volume, tone controls, filters).

400uV noise floor on 0.5mV, 5mV phono inputs and 150mV line input would be at -2dB, -22dB and -51dB respectively.
 

Offline smugtronix

  • Contributor
  • Posts: 28
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #11 on: October 31, 2012, 09:16:35 am »
Are those little brown caps (I'm assuming polypropolene or stacked metal film) Panasonics, or are they some one-hung-low brand? I'd be interested to see what they use for caps in that price range.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #12 on: October 31, 2012, 09:25:42 am »
Interesting, some youtuber suggests C405. Found it in the schematic but can't figure out what it might do. Some kind of AC power detection logic?
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #13 on: October 31, 2012, 09:43:33 am »
Interesting, some youtuber suggests C405. Found it in the schematic but can't figure out what it might do. Some kind of AC power detection logic?
Looks like zero crossing detector and power for the 4013 chip.

When the voltage in C411 (the output filter cap) gets too high, it turns on IC403 which pulls the Data pin (pin 5) of the 4013 down. On the next rising edge of the mains input the chip switches off its output and, in turn, the transformer. When the output voltage gets too low, IC403 switches off and the ata pin gets pulled up by R414 and on the next cycle Q404 switches on.

The chip is powered trough the cap (and D406) too.

This is kind of slow PWM, most likely made so that it does not introduce wideband noise to the amp.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #14 on: October 31, 2012, 09:47:18 am »
Interesting, some youtuber suggests C405. Found it in the schematic but can't figure out what it might do. Some kind of AC power detection logic?
Looks like zero crossing detector and power for the 4013 chip.

When the voltage in C411 (the output filter cap) gets too high, it turns on IC403 which pulls the Data pin (pin 5) of the 4013 down. On the next rising edge of the mains input the chip switches off its output and, in turn, the transformer. When the output voltage gets too low, IC403 switches off and the ata pin gets pulled up by R414 and on the next cycle Q404 switches on.

The chip is powered trough the cap (and D406) too.

This is kind of slow PWM, most likely made so that it does not introduce wideband noise to the amp.

Yeah, I noticed the output pulsing at around 700mV (for the 10.5V), which is quite high, but it was at a low frequency, so I guess it would be inaudible. Anyway, that is only for the standby supply, to click the relay and maybe a few other digital things -- unlikely to be used in the analog section (I'd take a guess that the 10000u 16V Nichicons have something to do with that?)

I wonder how long this amp would run with no power and the AC detect disabled. It has enough capacitance in it! I modded my cheap computer speakers to have a 6800µF bulk cap because the transformer was dropping out on high peaks (470µF was the original.) Now they last 3-4 seconds with no power and ordinary music.   ::)
 

Online mzacharias

  • Frequent Contributor
  • **
  • Posts: 537
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #15 on: October 31, 2012, 09:53:35 am »
I can provide service literature and technical support. I work on these types all the time.
 

Online mzacharias

  • Frequent Contributor
  • **
  • Posts: 537
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #16 on: October 31, 2012, 10:02:44 am »


Yamaha Training video on their "green" power supplies.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #17 on: October 31, 2012, 10:20:26 am »
Useful video, but his advice about removing the ground on the scope, or isolating the scope is dangerous. The hifi amplifier should always be the isolated part.

I also suspect it doesn't work quite as he says - the data pin should be high most of the time (it essentially equals Vcc when opto off), the clock latches this data in (from the AC), which turns off the FET (through not-Q.) When data falls low, it latches that in, which turns on the FET. It ensures the transformer only ever sees 0V or one AC cycle (full cycle due to half-wave rectifier), quite neat actually...

I have also always wondered if there's a good reason not to use that full wave rectifier with FET to switch low voltage, high current AC -- over using a triac, for example.
« Last Edit: October 31, 2012, 10:22:23 am by tom66 »
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 28143
  • Country: au
    • EEVblog
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #18 on: October 31, 2012, 10:52:23 am »
Yamaha Training video on their "green" power supplies.

Youtube has a video for everything!, what are odds?

Anyway, followup:
It was C405, a 22nF metalised polyester film cap, 630V.
It read low, about 500pF.
A common fault in these Yamaha's apparently, and a few Youtube commenters pointed it out.

Dave.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #19 on: October 31, 2012, 11:00:35 am »
Yamaha Training video on their "green" power supplies.

Youtube has a video for everything!, what are odds?

Anyway, followup:
It was C405, a 22nF metalised polyester film cap, 630V.
It read low, about 500pF.
A common fault in these Yamaha's apparently, and a few Youtube commenters pointed it out.

Dave.

Follow up video! Follow up video!
:D
Pweeeeease...

Reminds me of a proud "dumpster" find. My brother told me his garage needed cleaning out, anything I wanted I could keep, got a faulty Xerox 19" monitor (7 bad caps, easy fix), and a nice working surround amp (but for a computer, not as good as the Yamaha.) Along with other bits of useful gear like network switches.
« Last Edit: October 31, 2012, 11:02:53 am by tom66 »
 

Online mzacharias

  • Frequent Contributor
  • **
  • Posts: 537
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #20 on: October 31, 2012, 11:23:52 am »
Yamaha Training video on their "green" power supplies.

Youtube has a video for everything!, what are odds?

Anyway, followup:
It was C405, a 22nF metalised polyester film cap, 630V.
It read low, about 500pF.
A common fault in these Yamaha's apparently, and a few Youtube commenters pointed it out.

Dave.

Not a Youtube video as such. I had it available as an authorized servicer and made it available only through this link. It's not my policy to release potentially dangerous information to the public.

Mark Z.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #21 on: October 31, 2012, 11:31:15 am »
I am of the opinion, if someone with no electronic experience is dumb enough to open their product and get electrocuted (which is easy to avoid by following simple precautions), then they have made a mistake in the first instance, and lack of service information won't stop them. In fact, if anything, it might lead to more shocks due to it being harder to determine the high/low voltage parts of the circuit and which parts, if any, are safe to touch.
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 28143
  • Country: au
    • EEVblog
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #22 on: October 31, 2012, 11:48:15 am »
Follow up video! Follow up video!
:D
Pweeeeease...

Rendering now...

Dave.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #23 on: October 31, 2012, 11:51:41 am »
Follow up video! Follow up video!
:D
Pweeeeease...

Rendering now...

Dave.

Dammit, now I won't be able to get up at 10am for lectures!
I hate you, and love you, simultaneously.
 

Offline Psi

  • Super Contributor
  • ***
  • Posts: 6821
  • Country: nz
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #24 on: October 31, 2012, 12:14:14 pm »
A good thing about those sort of set top surround amps is that the amplifier PCB is often separate and only needs power and signal.

It's normally pretty trivial to rip out everything but the transformer and amp board then feed the amp some line level audio.

Then you have a nice simple multichannel high power amp. :)
« Last Edit: October 31, 2012, 12:16:33 pm by Psi »
Greek letter 'Psi' (not Pounds per Square Inch)
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #25 on: October 31, 2012, 12:24:10 pm »
I wonder how long this amp would run with no power and the AC detect disabled. It has enough capacitance in it! I modded my cheap computer speakers to have a 6800µF bulk cap because the transformer was dropping out on high peaks (470µF was the original.) Now they last 3-4 seconds with no power and ordinary music.   ::)

Probably not very long as high quality amps have larger idle currents (it used about 40W when the relay was forced on). My tube headphone amp has 470uF and 330uF caps on B+, when I switch off the power tubes cool down faster than the caps discharge (that's why I have the bleeder resistor and a neon light to indicate whether it's still dangerous).
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 4932
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #26 on: October 31, 2012, 12:50:12 pm »
Useful video, but his advice about removing the ground on the scope, or isolating the scope is dangerous. The hifi amplifier should always be the isolated part.

I also suspect it doesn't work quite as he says - the data pin should be high most of the time (it essentially equals Vcc when opto off), the clock latches this data in (from the AC), which turns off the FET (through not-Q.) When data falls low, it latches that in, which turns on the FET. It ensures the transformer only ever sees 0V or one AC cycle (full cycle due to half-wave rectifier), quite neat actually...

I have also always wondered if there's a good reason not to use that full wave rectifier with FET to switch low voltage, high current AC -- over using a triac, for example.
I'm also surprised they used a relatively expensive MOSFET as opposed to a relatively cheap triac. Also, I don't see any snubbers to handle the inductive spikes, so I have no idea how it can be reliable. Apart from that, it's actually an interesting way to "period skip" a linear power supply!

Nowadays, they would just use a small switching power supply based on a single chip flyback converter. And the main power supply would be a switching unit as well (similar to a PC power supply), with variable output voltage in the fancier units.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline wastrix

  • Contributor
  • Posts: 5
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #27 on: October 31, 2012, 01:20:49 pm »
Yamaha Training video on their "green" power supplies.

Youtube has a video for everything!, what are odds?

Anyway, followup:
It was C405, a 22nF metalised polyester film cap, 630V.
It read low, about 500pF.
A common fault in these Yamaha's apparently, and a few Youtube commenters pointed it out.

Dave.
Yep, I've repaired quite a few of these Yamaha receivers, every single time it was that cap. The boss rarely bothered checking anything else, just replaced that cap as a matter of course and 99% of the time that fixed it.

Quick way to make up an $80 service charge!
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #28 on: October 31, 2012, 02:04:06 pm »
I also suspect it doesn't work quite as he says - the data pin should be high most of the time (it essentially equals Vcc when opto off), the clock latches this data in (from the AC), which turns off the FET (through not-Q.) When data falls low, it latches that in, which turns on the FET. It ensures the transformer only ever sees 0V or one AC cycle (full cycle due to half-wave rectifier), quite neat actually...
When data is low (opto is on) the FET would be turned off. Opto is turned on when the output voltage is too high.

Nowadays, they would just use a small switching power supply based on a single chip flyback converter. And the main power supply would be a switching unit as well (similar to a PC power supply), with variable output voltage in the fancier units.
Switching power supplies have more noise on the output than linear power supplies. Cheaper receivers use them of course, but the higher quality ones probably still use linear supplies (I do not have a new receiver, so I cannot take it apart and look). On the other hand I still prefer hard power switches instead of the soft ones. When I switch off the power to my amp it consumes 0W.
 

Offline kyndal

  • Contributor
  • Posts: 34
  • Country: ca
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #29 on: October 31, 2012, 03:18:11 pm »
i fixed a similar AV unit a few years back..  although it was an ONKIO? brand or something rather..

but ya  turned out to to be a failed Film cap aswell.   Took FOR EVER!!.
(including switching the board with a working one)
then basically de-soldering every part and test out of circuit
Sigh.

i guess these days.. with youtube and what have you.. i could have saved myself a few gray hairs
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 4932
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #30 on: October 31, 2012, 04:22:33 pm »
Switching power supplies have more noise on the output than linear power supplies. Cheaper receivers use them of course, but the higher quality ones probably still use linear supplies (I do not have a new receiver, so I cannot take it apart and look). On the other hand I still prefer hard power switches instead of the soft ones. When I switch off the power to my amp it consumes 0W.
That noise is mostly irrelevant in modern digital equipment. The digital logic doesn't mind as long as it can reliably distinguish 1s and 0s, and it's a digital signal all the way to the power stage. Where the signal does become analog occurs at rather high power levels, where a little noise would have no effect. The whole thing operates just like a low voltage servo motor drive. (Which if you think about it, that's exactly what it is...) Some manufacturers like Samsung are going as far as putting the modulators, drivers, and power MOSFETs in the same chip.

Reducing the supply voltage at low volume settings reduces the losses in the power stage and also allows the entire dynamic range of the Delta Sigma modulators to be used at low volume.

If the only inputs have their own power (like USB and HDMI), they could use that to activate the relay and eliminate all standby power use while retaining automatic power on. The problem is that the legacy analog and S/PDIF inputs don't have power as such and cannot reliably power anything. It might be possible with analog but it would rely on working with a low impedance source with a significant voltage level. (They could use a transformer to boost the voltage to charge a cap, which is later switched out when main power is on.) It could possibly work with coaxial S/PDIF as well but optical S/PDIF would be basically impossible. A possible workaround might be to have a momentary mains button across the relay, to allow it to be switched on for legacy inputs.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #31 on: October 31, 2012, 06:24:30 pm »
That noise is mostly irrelevant in modern digital equipment. The digital logic doesn't mind as long as it can reliably distinguish 1s and 0s, and it's a digital signal all the way to the power stage. Where the signal does become analog occurs at rather high power levels, where a little noise would have no effect.
But the amp has analog inputs, which care about noise. Or maybe modern amps do not have them, I wouldn't know as I would not buy an amp that does not have analog inputs.
 

Online oPossum

  • Frequent Contributor
  • **
  • Posts: 595
  • Country: us
  • The other white meat
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #32 on: October 31, 2012, 06:26:53 pm »
Shouldn't that be a X2 rated cap?
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #33 on: October 31, 2012, 07:33:41 pm »
I wouldn't have thought higher ripple; otherwise, it would likely still turn on once in a while. That C405 is a capacitive supply for the d-type. It provides a ~8-10V or so supply. The 6.8V zener powers an optocoupler. If the optocoupler output goes out the secondary senses an error, even if the PSU keeps working.
 

Online mzacharias

  • Frequent Contributor
  • **
  • Posts: 537
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #34 on: October 31, 2012, 08:23:31 pm »


Troubleshooting waveforms.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #35 on: October 31, 2012, 08:57:19 pm »
LOL, the switched outlets were rated for ~100W so they used a 2A fuse, but users kept plugging in high power devices and blowing the fuse, so they replaced it with 10A. Now the relay will probably melt before the fuse does (since it is probably rated for only 10A).
 

Offline EEVblog

  • Administrator
  • *****
  • Posts: 28143
  • Country: au
    • EEVblog
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #36 on: October 31, 2012, 09:47:05 pm »
Shouldn't that be a X2 rated cap?

It was not fitted with an X or Y rated cap, nor was it specified. It was a bog standard 630V metal poly.

Dave.
 

Online oPossum

  • Frequent Contributor
  • **
  • Posts: 595
  • Country: us
  • The other white meat
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #37 on: October 31, 2012, 09:53:54 pm »
I know it wasn't specified, but that type of power supply typically has a X2 cap and a power resistor for inrush current.

Seems like a flawed design that has an above average failure rate.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #38 on: October 31, 2012, 10:37:07 pm »
I think it should be an X2 cap, as a normal poly may burn under failure. The 2.2k might be a fusible resistor though -- so they might be allowed to use an ordinary poly.
 

Offline jaycee

  • Regular Contributor
  • *
  • Posts: 178
  • Country: gb
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #39 on: October 31, 2012, 10:40:05 pm »
A guy with one of these appeared on DIYAudio a month ago actually ! Despite having never seen it before, my suspicion fell on C405 immediately. In that case, the guy had measured the primary voltage of the transformer and found it was low. I did have a WTF moment when I saw the flipflop being used, but after a minute or two I suspected they were using it to pulse feed the primary rather than running it directly from line voltage.

It looks like they should have specified an X2 rated part, but the bean counters decided to cut a few cents and made it an ordinary film cap. The problem is, this cap will see all sorts of line spikes, which will ruin it. If they had put a VDR across the mains input, it might have been OK. Bean counters again! An X2 rated dielectric would have had some self healing properties which would have allowed it to tolerate line spikes, and the unit would have been reliable in the field. It is just as well the film capacitor they chose fails open, or there could have been a fire hazard!

As someone else mentioned, C405 is functioning as a dropper due to reactance. This was quite common for small "off line" supplies before SMPS became so easy/cheap to produce. That produces the voltage that the flipflop runs on. Also they are using it to AC couple the line frequency in, and the thing overall functions a bit like a light dimmer. My guess is because the MOSFET wasn't firing often enough due to the low coupling capacitance, there was the correct voltage on the secondary but not enough current backing it. The micro probably ran OK, but as soon as it tries to switch on the relay, the voltage collapses, resetting the micro - so all seems dead.

To those who have said "nowadays this would be an SMPS", true... the standby supply likely would be. However, the main supply, it depends. Class D (PWM) amplifiers are now becoming common for receivers due to their high efficiency and low heat output, and these are perfectly happy with an SMPS supply. On the other hand, a lot of high quality audio is still done with Class AB amplification, and it takes a LOT of effort to get a clean enough output from an SMPS. So typically, if it's Class AB, it will use a good old linear power supply.
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #40 on: October 31, 2012, 10:44:23 pm »
If I were designing this, and I had to keep the 1W standby, I'd use a 680k/1W resistor in place of that cap, and replace the electro with one a little bigger, maybe 47µF (good high reliability cap), to give it some "backup". A separate tap off the transformer would provide some extra power once the circuit starts. It would use about 0.2W more, because of the resistor power dissipation, but would be more reliable. This is similar to the design in switch mode power supplies, but using lower frequency pulsing.

The 22nF cap has an impedance of 144k at 50 Hz, it is clearly used as a capacitive dropper, but these circuits don't seem to be very reliable. Since it was still oscillating down to 500pF, that is impressive...
 

Offline jaycee

  • Regular Contributor
  • *
  • Posts: 178
  • Country: gb
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #41 on: October 31, 2012, 11:01:44 pm »
tom66, if you were designing this today you'd use one of those one-chip SMPS's with onboard MOSFET. A bridge, a 400V electrolytic cap, the IC, a transformer, a few passives and bingo :) Same sort of thing they bundle in wall warts nowadays.

The Yamaha is not that old though, so I guess they chose this circuit for noise reasons. Probably easier to pass regulatory compliance too.
 

Offline Salas

  • Frequent Contributor
  • **
  • Posts: 291
  • Country: gr
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #42 on: October 31, 2012, 11:53:41 pm »
jaycee, your explanation is right on the money. That MKT film should be punched inside like Swiss cheese by now. Takes X2 rated or 1000V polypropylene film and foil pulse caps, polypropylene is self healing also. C405 stole Dave's thunder in the land of down under. Bummer.
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 4932
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #43 on: November 01, 2012, 12:23:52 am »
But the amp has analog inputs, which care about noise. Or maybe modern amps do not have them, I wouldn't know as I would not buy an amp that does not have analog inputs.
The legacy analog inputs are converted to digital to drive the modulators. That part is quite small and easy to shield.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #44 on: November 01, 2012, 12:48:31 am »
But the amp has analog inputs, which care about noise. Or maybe modern amps do not have them, I wouldn't know as I would not buy an amp that does not have analog inputs.
The legacy analog inputs are converted to digital to drive the modulators. That part is quite small and easy to shield.
So I made the right choice in buying an older amp that is all analog - no A->D->A conversion adding noise and distortion and the circuit diagram is easier to understand. So, no new amps that use class A/AB, but are not audiophile-grade (and cost)?
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #45 on: November 01, 2012, 12:58:06 am »
Plenty of new amps use class-AB (my brother bought one just a year ago -- a Denon 7.1 system), it's just it's becoming less common because you can reach the same performance with class-D nowadays. The only benefit is either wanting a nice room heater, or for audiophiles who like "the sound" of class-AB.
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15050
  • Country: za
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #46 on: November 01, 2012, 03:09:33 am »
I have a similar one with a bad Dolby processor, low audio on the main channels but ok on surround info. Not the amplifiers but somewhere in that jungle of switching. Similar looking bard but has a dolby chipset in it. Must look at the model and see if i can get a manual for it and bypass the logic.

Anther is an Onkyo with a bad amplifier, needs about 10 transistors changed ( bloody expensive FET's as well, so not likely to be done) and they are of course on the massive heatsink buried in the bottom of the chassis, with the entire thing built on top of it. Switches on and works, but gets very toasty very fast then does a thermal shutdown, with one distorted channel.
 

Offline Salas

  • Frequent Contributor
  • **
  • Posts: 291
  • Country: gr
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #47 on: November 01, 2012, 10:18:42 am »
Shouldn't that be a X2 rated cap?

It was not fitted with an X or Y rated cap, nor was it specified. It was a bog standard 630V metal poly.

Dave.

They designed and tested at 110VAC then they negotiated a 630V MKT type in large quantity and in several values for their whole production range. The large voltage margin will cover X spec inability they rest assured, is my scenario. Did the final boards, and went to production. Then all the 230-240VAC countries importers started receiving units to repair. They simply did not test at 240VAC. Was late, no X2 or 1000V PP cap at that size and value. My wild scenario, but if those units are not committing  suicide like Lemmings in America too, it maybe holds some water. 8)
 

Offline Salas

  • Frequent Contributor
  • **
  • Posts: 291
  • Country: gr
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #48 on: November 01, 2012, 11:24:07 am »
Found the excellent jaycee reference thread too. Interesting on how they tackled it not long ago.

http://www.diyaudio.com/forums/solid-state/216317-yamaha-dsp-ax750se-dead-no-power.html
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 4932
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #49 on: November 01, 2012, 01:53:13 pm »
So I made the right choice in buying an older amp that is all analog - no A->D->A conversion adding noise and distortion and the circuit diagram is easier to understand. So, no new amps that use class A/AB, but are not audiophile-grade (and cost)?
If you're using only "legacy" analog sources, then perhaps. There's the option of using a "hybrid digital" amplifier that gives the great efficiency of a digital amplifier without having to (in the traditional sense) convert the signal to digital. But if you're starting from a digital signal, going with a "pure digital" amplifier gives the best audio quality. In theory, it's possible to build an amplifier that can be switched between hybrid digital and pure digital operation (reusing the power supply and power stage), but I have never seen such a design.

Something I really like about analog is that mixing two signals can be done as easily as using a bunch of resistors. Doing it on digital would take a FPGA or ASIC and dealing with slightly different clock frequencies is a surprisingly complicated matter.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #50 on: November 02, 2012, 10:27:05 am »
If you're using only "legacy" analog sources, then perhaps. There's the option of using a "hybrid digital" amplifier that gives the great efficiency of a digital amplifier without having to (in the traditional sense) convert the signal to digital.
When I am choosing an amplifier, the efficiency does not really matter to me. I do not need a very powerful amp (2x100W is enough, at least for the speakers I have) and I am not using it 24/7 at full power, so I'd rather have higher sound/build quality, more tape loops or a cheaper amp. My sources are mostly analog too, I have a PC and a CD player connected to the amp, but the analog connection has enough quality for me (I could always use an external DAC if I really wanted to).

I have a little class D amp (2x5W or so) about the size of a Socket A CPU. It sounds OK, unless some peak drives it to distortion, then there is a lot of distortion. Also the amp causes quite a lot of noise on the radio.
 

Online mzacharias

  • Frequent Contributor
  • **
  • Posts: 537
  • Country: us
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #51 on: November 02, 2012, 11:00:22 pm »


They designed and tested at 110VAC then they negotiated a 630V MKT type in large quantity and in several values for their whole production range. The large voltage margin will cover X spec inability they rest assured, is my scenario. Did the final boards, and went to production. Then all the 230-240VAC countries importers started receiving units to repair. They simply did not test at 240VAC. Was late, no X2 or 1000V PP cap at that size and value. My wild scenario, but if those units are not committing  suicide like Lemmings in America too, it maybe holds some water. 8)
[/quote]

Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.
 

Offline nitro2k01

  • Frequent Contributor
  • **
  • Posts: 844
  • Country: 00
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #52 on: November 03, 2012, 05:48:13 am »
mzacharias, what if they had put two of those in series? Double tolerance. Bigger drop, but that's ok since the voltage is double. Only problem is how to mount them.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #53 on: November 03, 2012, 06:42:30 am »
Or use 1kV ones, I have seen them readily available. Or a resistor and second tap off trafo (best solution IMO.)
 

Offline JoannaK

  • Frequent Contributor
  • **
  • Posts: 337
  • Country: fi
    • Diytao making blog
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #54 on: November 03, 2012, 07:18:38 am »


Troubleshooting waveforms.

Thanks.. New things learned today, thanks to you, Dave and the whomever (sorry, didnt check the name etc) at Yamahe doing those videos.

 

Offline Salas

  • Frequent Contributor
  • **
  • Posts: 291
  • Country: gr
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #55 on: November 05, 2012, 01:55:56 am »
Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.

Thanks for the info. They should have developed that PSU in a 110V lab building confidence all along for the component choices as well then. 240V mains slowly degrading that MKT inside takes long enough to have escaped their international models probably shorter pre production testing it seems. 
 

Offline T4P

  • Super Contributor
  • ***
  • Posts: 3706
  • Country: sg
    • T4P
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #56 on: November 06, 2012, 11:00:25 pm »
Plenty of new amps use class-AB (my brother bought one just a year ago -- a Denon 7.1 system), it's just it's becoming less common because you can reach the same performance with class-D nowadays. The only benefit is either wanting a nice room heater, or for audiophiles who like "the sound" of class-AB.
They absolutely hate the sound of AB, they want Class-A!

When I am choosing an amplifier, the efficiency does not really matter to me. I do not need a very powerful amp (2x100W is enough, at least for the speakers I have) and I am not using it 24/7 at full power, so I'd rather have higher sound/build quality, more tape loops or a cheaper amp. My sources are mostly analog too, I have a PC and a CD player connected to the amp, but the analog connection has enough quality for me (I could always use an external DAC if I really wanted to).

I have a little class D amp (2x5W or so) about the size of a Socket A CPU. It sounds OK, unless some peak drives it to distortion, then there is a lot of distortion. Also the amp causes quite a lot of noise on the radio.
Socket A? Must be quite old Class D tech also, many folks bang on about inefficiency so we give them good Class-D now!

Worked on dozens of Yamaha's with this type of power supply. Never seen that cap go bad in the American version - only ever heard of it from the 240V models.

Thanks for the info. They should have developed that PSU in a 110V lab building confidence all along for the component choices as well then. 240V mains slowly degrading that MKT inside takes long enough to have escaped their international models probably shorter pre production testing it seems.
How do you ever know? Japan's power supply is 110V @ 60Hz! It's a definitely thing that they will have a variable AC source but i guess it takes a long time for the MKTs to slowly eat itself out
 

Offline SeanB

  • Super Contributor
  • ***
  • Posts: 15050
  • Country: za
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #57 on: November 07, 2012, 02:27:12 am »
Japan has110VAC 60Hz and 220v 50Hz, and there are areas where the two are intermingled. Why do you think they leapt so fast onto autoswitching voltage power supplies, while the rest of the world was using a switch on the back of the equipment.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #58 on: November 07, 2012, 07:41:33 am »
Socket A? Must be quite old Class D tech also, many folks bang on about inefficiency so we give them good Class-D now
Well, the most space on the board is taken up by a 2200uF/25V capacitor. The amp is based on a chip (the chip is under a heatsink, so I do not remember which one) and is available from China on ebay.

It does not seem to have any output filters, so while it sounds OK, I don't turn it on wen I am listening to FM radio.

As for the efficiency - to me efficiency matters the most on battery powered devices (unless the device is big and can have a big battery), it also matters a bit on high power devices that I keep on 24/7, but for something like an amp I'd rather have higher quality (or a tube amp, even if the sound was the same, tubes are cool).
 

Online NiHaoMike

  • Super Contributor
  • ***
  • Posts: 4932
  • Country: us
  • "Don't turn it on - Take it apart!"
    • Facebook Page
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #59 on: November 07, 2012, 01:27:19 pm »

That explains how the Delta Sigma modulators in a digital amplifier work. As noted, a higher carrier frequency gives better quality (most amps run at a few hundred kHz with some going into the low MHz), but having more orders in the modulator also helps (at the expense of being harder to design).

BTW, if you're starting from digital, the process to convert it to analog likely goes through Delta Sigma in any case. Therefore, digital input amplifiers make a lot of sense with digital sources.
Cryptocurrency has taught me to love math and at the same time be baffled by it.

Cryptocurrency lesson 0: Altcoins and Bitcoin are not the same thing.
 

Offline Pentium100

  • Regular Contributor
  • *
  • Posts: 245
  • Country: lt
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #60 on: November 08, 2012, 06:29:00 am »
BTW, if you're starting from digital, the process to convert it to analog likely goes through Delta Sigma in any case. Therefore, digital input amplifiers make a lot of sense with digital sources.
Well, I guess if you have only digital sources you might as well use a modulator that can provide a lot of current to drive the speakers. On the other hand, as I recall, there are also multi bit DACs (essentially a network of very precise resistors), but I do not remember what their pros and cons are compared to single bit DACs.

Still, for me analog-only amplifier is better, since I have a lot of analog sources (and for my digital sources, if I want, I can get an external DAC independent of my amp).
 

Offline tom66

  • Super Contributor
  • ***
  • Posts: 3374
  • Country: gb
  • Electronic Engineer & Hobbyist
Re: EEVblog #378 - Dumpster Diving Teardown Repair
« Reply #61 on: November 09, 2012, 09:36:22 am »
Japan has110VAC 60Hz and 220v 50Hz, and there are areas where the two are intermingled. Why do you think they leapt so fast onto autoswitching voltage power supplies, while the rest of the world was using a switch on the back of the equipment.

Japan is 100V all around, it is just the frequency which is different. 50 Hz in the east, 60 Hz in the west. For old transformer supplies, I think you could get away with using a 50 Hz transformer, it would work acceptably at 60 Hz (but not the other way around...)
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf