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DVD player power supply circuit strange behavior

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DVD player power supply circuit strange behavior

Postby longgu » Tue Jan 02, 2018 3:14 am

Hello guys, first post here, please be kind. :-D The situation is following: 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).
Thanks all!
I'm sorry I can't upload my pictures because of the new permission.
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Re: DVD player power supply circuit strange behavior

Postby Bob » Tue Jan 02, 2018 6:50 am

Check the voltage regulator ICs. In a power supply like this, the regulator establishes the voltage. Typically, there will be a 12v and a 5v regulator IC. A 17v level suggests the 12V regulator may be bad.
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