DVD Player Power Supply Repair

[fusekiller]

Hi,

I try to repair this power supply of a DVD player. The +12v rail measures 8.5V, the -12V rail is -9V both with no ripple. All other voltages are ok.
I checked the filter caps with an ESR meter but they all seem ok.
What can I try next? I have no schematics and btw. I am not a switch mode power supply expert. 

Thanks for any help!

[Srbel]

Check if the voltage reference is giving the correct voltage and if feedback ressistors are of correct ressistance.

[grumpydoc]

The chances are that the circuit is not a million miles from this:



Which I found by googling for 5LO380R application notes/datasheets/circuits - your board doesn't have any linear regs on the secondary side though so just ignore the stuff to the right of the vertical line through C18, C19, C20, C21 and C22.

The regulation will just be picked up from one of the rails - probably 5V so that only really leaves the very few secondary side components in the +/- 12V rails to be a problem.

That's IF the PSU is the problem - have you checked whether feeding in +/- 12V makes the player work?

[fusekiller]

That's IF the PSU is the problem - have you checked whether feeding in +/- 12V makes the player work?

Good point! I powered the DVD drive from an external supply and it still did not accept any disk. The I tried a PC drive I had lying around and now the player works, even with the internal power supply which I suspected to be faulty.
The display becomes significantly dimmer every time when the drive (even the original one) draws current. So maybe the PSU is not 100% ok, but it does the job.
In the next step I'll try to adjust the pots on the laser unit which I have sucsessfully done several times before.

Thanks everyone for the hints, I will keep them in mind for the future!