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I have an old (~8 yrs) Cyberhome dirt cheap DVD player that worked well for the time I was using it. I bought it in 2004 from a Best Buy and was using it regularly till 2010. After we got a new DVD player, it had been lying around packed nicely and securely. I recently brought it out just to connect it to another TV and found that it doesn't power on. I opened it up and was able to isolate its power supply (the pic shows it was very easy to do so). It works from 110 V to 240 V AC input 50-60 Hz. I have been using it in India which has 240 v AC @ 50 Hz usually. The DC out of the power supply circuit is like so +5V-GND-GND-+12V. I have assumed that the +5V was for the decoding circuit while the +12V would have been used by the player motor and maybe also the Class 1 laser. The +5V out works fine, but the +12V doesn't. The first time I checked it showed +17V and remained steady there. When I switched off the power, it very slowly (over 10-15 mts) ramped down to nearby 0 V. Based on this, I decided to wire up a voltage divider to bring 17 to 12 on a breadboard. Before I connected the +17V to the voltage divider, I checked again to make sure and now it showed ~+12V! It was slowly ramping up and 5 mts later was at +14.30V and has been holding steady there since last 10-15 mts. Switching off the power supply doesnt slowly ramp it down but goes down to 0 V pretty fast.

What is the reason for such behavior? Obviously, something has gone poof in the power supply circuit, and I am interested to know the root cause. Some pointers will definitely help and using those I may try to debug through the board to figure out more. (I plan to wire up the input of the system to +5V-GND-GND-+12V independent of this power supply board to check the player but that's later as I don't have a +12V source handy currently. I tried with +5V and the dvd player powers on fine - but without the +12 doesn't do much apart from that).

enter image description here

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  • \$\begingroup\$ If it helps, there is also a faint high pitched tone coming from the power supply board as long as it has input power. Is that normal? \$\endgroup\$ – Sushrut J Mair Jan 1 '13 at 15:37
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    \$\begingroup\$ My first thought is a capacitor, they can go bad just sitting around and they can make noise. There is nothing visually obvious to me in the picture though. \$\endgroup\$ – adam W Jan 1 '13 at 16:11
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    \$\begingroup\$ These type of power supplies have a need for a certain amount of load or they don't work right. Did you add a high power resistor or some circuit that can draw tens or maybe hundreds of miliamps? \$\endgroup\$ – Gustavo Litovsky Jan 1 '13 at 17:17
  • \$\begingroup\$ Nope no loads... \$\endgroup\$ – Sushrut J Mair Jan 5 '13 at 5:17
  • \$\begingroup\$ Thanks for all the pointers. I am going to try something a little different (rather than troubleshooting the existing power supply board). I am planning to get a +12V power supply and use it with the +5V in a common ground configuration to see if everything works fine. \$\endgroup\$ – Sushrut J Mair Jan 5 '13 at 5:21
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Most likely there's nothing severely wrong with the power supply.

Your description leads me to believe that the power supply has its feedback on the +5V rail and having zero load on the +12V rail causes it to drift high. In the application (the DVD player) there's always load on the +12V rail which keeps the output closer to +12V.

High-pitch acoustic noise often comes from ceramic capacitors or the magnetic components. A faint noise is generally not a cause for concern - it was most likely always there but when it was enclosed you couldn't hear it.

That being said, it's possible that the power supply can no longer deliver its rated current, or the rest of the hardware is drawing too much current and forcing the power supply to protect itself. You need to check for short-circuits and dried-out electrolytic capacitors on both the power supply and in the rest of the DVD player itself, as well as probe any diodes and transistors you can find. ICs are tricky (especially if the unit is using some custom ASIC).

(Realistically, the way consumer electronics are designed these days, eight years is a remarkably-good run for a device that most likely only came with a 1-year warranty.)

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  • \$\begingroup\$ Thanks for the inputs - I have tried reconnecting to see if load via the dvd player helps, but didn't work out. \$\endgroup\$ – Sushrut J Mair Jan 5 '13 at 5:20
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Is it my imagination that the below shown two capacitors have a slightly bulged top? If so it could be a strong indicator to replace all the caps on the power supply board.

enter image description here

The appearance could just be an angle of the lighting.

I do have to say that I replaced all the caps on the power supply board of a friends LCD TV. In that case the reported problem was that the TV would not turn on. None of the capacitors showed any sign of leakage or bulging but I replaced them all anyway. He reinstalled it and announced that his TV is now powering up and working!!

Power supplies in this consumer equipment are so competitive and built so cheaply. A common indicator is the one sided phenolic boards that are used and the strange off brands of electrolytic capacitors that are installed. In the past three years I've personally replaced the power supply caps in about 15 LCD monitors that ranged in age from 3 to 6 years and restored them to functionality by doing so. In fact I'm using two of those monitors right now as I type this.

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  • \$\begingroup\$ Not all cap failures result in obvious end-vent popping. Re-capping is always a good blind troubleshooting technique, so long as the capacitors that are being installed are of the correct ratings. \$\endgroup\$ – Adam Lawrence Jan 1 '13 at 22:21
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Q. if it has a 12V regulator then it might be shorted. 17V in 12V out. The 17V is bleeding down faster because the divider network you installed is providing a lower resistance path at switch off than without it thus discharging the storage capacitor quicker, search (time constants regarding capacitors). Being cheap it is worth while to change at least the capacitors on the primary side of the supply (between the fuse and the blue chopper transformer) If you measured 17V whilst everything was connected and turned on then the 17V rail is on load and if the supply requires a load to regulate down to 12V (poor state of affairs) (but you did say it was a cheapy,as most things are nowadays) But for us curious and courageous ones, us who "need" to know I say press on dear fellow and fix everything that has died before we get buried in this stuff.

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Try changing those bulging capacitors and use viable parameters to check the other components. Clean the equipment to make sure the dust does not add unknown resistance to the output regulator. This can manually re-program the output voltages when the whole power pack is still perfectly working.

This can also happen when the resistances on the 4 3 1 labelled transistor on the secondary shed a shunt or increase in resistance. This can actually lower or increase the output voltage respectively which is what you are taking about.

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    \$\begingroup\$ One single sentence. Impressive. \$\endgroup\$ – winny Jun 26 '17 at 20:09

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