Dynex do-l40-10a power supply transformer buzzing

[Kawboy]

I am working on a 40" dynex that never powered back on after a storm. There is no obviously visible problem on the boards but the transformer on the power supply is buzzing/ticking the plug that feeds the inverter board test good at 26v.

The larger plug that feeds to the main board however has some issues. There are two 12v and two 5v pins that when tested show low and erratic voltage that seems to correspond with the transformer ticking. The pin that is supposed to be 5v test 2.4v when first plugged in and it will work its way up to just above 5v and then there is a click and every thing goes dead. The 12v pin acts the same way but initially tests around 8v.

Is the transformer itself failing or could it be something else? Any help is greatly appreciated.

[CapLeaker]

Re: Dynex do-l40-10a power supply transformer buzzing

disconnect the main board and see if the 5V STBY stays stable on the PSU. Also we are going to need hi res, straight shot pictures, incl. the pin out of the PSU (PSU->main board).

[Kawboy]

Re: Dynex do-l40-10a power supply transformer buzzing








I disconnected the main board and all noise goes away. The two 5v test points had a steady 4.89v and no other pins have power

[CapLeaker]

Re: Dynex do-l40-10a power supply transformer buzzing

Plug the main board back in, turn on the TV and measure that STBY pin and see if that is steady 5V. Then measure On/OFF and the BL On/Off pin and report back.

[Kawboy]

Re: Dynex do-l40-10a power supply transformer buzzing

Thanks for the help. With the board plugged in the ticking is back( sounds like a watch but twice as fast. The top 5v standby reads a fluctuating 2.78 to 2.79
The bottom 5v stb reads a steady 4.817 and the on off reads the same fluctuating 2.78 to 2.79

After a few min there's a click and I loose everything until I unplug it and plug it back in

[CapLeaker]

Re: Dynex do-l40-10a power supply transformer buzzing

to check your PSU, unplug the mainboard and only leave the back light connected. Take a 1k resistor and jump STBY to ON/OFF and another 1k resistor from STBY to BL On/Off. When you plug the PSU in, the back light should be on and all voltage rails on the PSU should be up and running. With each click, does the voltage disappear on some of those pins I asked you earlier?

[Kawboy]

Re: Dynex do-l40-10a power supply transformer buzzing

I'll have to run grab some resistors tomorrow. The clicking only seems to affect the voltage on the non standby +5v vsb and +12 v pins There are two of each

[budm]

Re: Dynex do-l40-10a power supply transformer buzzing

These are the pins and pin functions of the power supply board connector pins:
STBY is the PS-ON pin.
SW is the BL-ON pin
BRI is the DIM control pin
The standby 5Vdc Voltage MAY BE the 5V_S pin or the 5V_M since one of these two is switched and one is ALWAYS there, you need to check that first before using the resistors for forcing on the power supply.