Need help, Sony HCD-SB500W protection.

[Pragmatiko]

Hi all, i have a strange problem with that home teathre.
If i turn on after 4 seconds goes in protection.
If i attach an headphone the item stay on and work.
I checked power amp board but have not found any short and all voltage are present.

Could you help me please thank you to all.

Here schematic

[Longbow]

Re: Need help, Sony HCD-SB500W protection.

Need more information. When the unit goes into protection, which outputs have a load? What is the load? What is the voltage on the speaker terminals with no load present? Confirm 3.3v, 12v and 15v is getting to the output IC. The headphones are driven by a totally different chip. Q101, 102, 103, and 104 are your protection transistors - what kind of voltages are on those transistors?

[Pragmatiko]

Re: Need help, Sony HCD-SB500W protection.

Hello, thank you very much for your interesting.
Well, maybe solved.
On SW output for a while i have voltage on output (both).
I have removed smd power amp IC (IC106 and IC107) and now all seem ok, then i suppose that IC are bad.

[CapLeaker]

Re: Need help, Sony HCD-SB500W protection.

... or just bad solder joint(s) on those output bricks.

[Pragmatiko]

Re: Need help, Sony HCD-SB500W protection.

... or just bad solder joint(s) on those output bricks.

no no... there was ic bad

[Chungalin]

Re: Need help, Sony HCD-SB500W protection.

From my historic register: I had one of these for repair back in 2006, it had DVD reading issues. Since problem was DVD related, I tested it without speakers (stupid weird speaker connectors instead of clips!!). At a given moment the unit shut off by itself and Standby LED kept blinking. No problem with headphones. After connecting speakers it all went fine. There was no reentry, so my conclusion was that it needs speakers to work properly (S-MASTER digital amp). But you never know. These units were quite new by 2006, perhaps still within warranty period.

Test it well with speakers before replacing those damn S-Master ICs.

[Longbow]

Re: Need help, Sony HCD-SB500W protection.

The power chips for the center and rear were taken out, but not the amp for the front channels. This would suggest a blown chip. I've never come across a class D amp that shut down because of no load. That would not make sense. I generally like to note down voltages on the pins before yanking a chip, especially an SMD, but since you already removed them I wouldn't put the same ones back in.

[JFA]

Re: Need help, Sony HCD-SB500W protection.

I have one of these home theatre systems with the problem described. Everything works fine with a headset plugged in but without it, the protection system operates. I have checked the speakers and wiring and all is OK. I have tried with and without speakers connected and using the systems speaker setup, I have changed the system to only run on the front and centre speakers but the problem still exists. I assume that the muting function of the headset stops power to ICs 101 through 107 and that my problem is on the amp board. My skills and equipment are probably not up to checking or changing these ICs but I'm willing to give it a go. Has anyone had any further experience with these machines before I dive in?

[CapLeaker]

Re: Need help, Sony HCD-SB500W protection.

Download the service manual above and look at the block diagram (page 27 of the pdf file) first. This way you get a rough idea on how this thing works and what IC does what. You also see that the audio out of the headphone jack has it's own headphone amp. That explains why you have audio there. So yes, I think you have a bad audio driver.

[JFA]

Re: Need help, Sony HCD-SB500W protection.

There is an "Amp Test" shown in the service manual that I cannot get to run. Also, should the unit function without speakers connected, previous poster, Chungalin had difficulties.
How can I check which IC is giving me grief, assuming that one is?

[CapLeaker]

Re: Need help, Sony HCD-SB500W protection.

Each driver has a overload detect circuit. Either you compare and measure those with the other channels or you compare the output drivers with each other. You can look for DC at the drivers outputs too. If you find one that is measuring different, take it out, turn on the amp and see what it does. Look at page 51, there is everything nicely on one page, from the driver, to the protection circuit down to the audio output end. Every driver has a 2 transistor protection circuit.

[JFA]

Re: Need help, Sony HCD-SB500W protection.

Thank you. Each IC is worth around $25 in Australia and I can't see myself removing one without destroying it in the process.

[CapLeaker]

Re: Need help, Sony HCD-SB500W protection.

Once you identified the bad one, use a dremel tool and cut off all legs first, then take the soldering iron and remove the rest of the legs with fresh solder. Them little legs come off like nothing. Or use a hot air soldering station.

[JFA]

Re: Need help, Sony HCD-SB500W protection.

Well I've measured the output to the overload detect circuit and can't find a difference. I've also measured the voltages at the various speakers and found that the two front and centre speakers read zero but the bass speakers flick up to 3V before the protection circuit operates when it drops to zero. I can only check voltages on the IC once the protection circuit kicks in. If it was only one of the bass speakers reading, I would definitely expect it to be the culprit but I'm not prepared to pull two ICs without some further investigation.

[budm]

Re: Need help, Sony HCD-SB500W protection.

You have two sets of sub-woofer (SW, IC106, IC107), so which one is showing 3VDC at the speaker terminals?

[JFA]

Re: Need help, Sony HCD-SB500W protection.

Both, that is why I am loathe to pull either driver.

[budm]

Re: Need help, Sony HCD-SB500W protection.

On page 69 of the service manual, you can see the internal block diagram of that Class D amplifier CXD9774M which you can test the INTERNAL POWER MOSFETs in the output sections to see if any of the 4 MOSFET has low resistance reading between PVDDA and OUT A, OUT A and GND, same test for the B section.

[JFA]

Re: Need help, Sony HCD-SB500W protection.

The readings between PVDDA and Out A, PVDDB and Out B, Out A and ground and Out B and ground are roughly 5Kohm for Front Left, Front Right and Centre. They are roughly 2.5Kohm for both Woofers except for PVDDB and Out B which are around 7Kohm for both woofers.
The protection kicks in now even with a headset plugged in. I don't know what any of this means but a new board is $250 so I am going to buy a cheap hot air de-solderer and go from there. Coming from China, it will probably take a good month to arrive so it will be a bit of a wait for any more progress.

http://www.ebay.com.au/itm/220V-Port...sAAOSwyQtVwZir

[JFA]

Re: Need help, Sony HCD-SB500W protection.

My hot air de-solderer finally arrived. All I managed to do was destroy the circuit board.

[CapLeaker]

Re: Need help, Sony HCD-SB500W protection.

that's too bad.