Long time lurker here. I've been subbed to Dave's You Tube channel since April 4th 2009. I wanted to share a recent repair of a Vizio E420-A0 TV.
Symptoms:
- When powering on the power LED would light up.
- Black screen
- No back light
- No audio or popping
- Zero image on LCD when looking with a flashlight
- Pressing the power button to turn the TV off would result in nothing. The power LED would still be on. Only unplugging the unit would reset it to the off state.
Diagnostics:
Power supply first....
- 5.2 volt standby rail was ok.
- When powering up the main 12 volt rail comes up as normal.
- When jumping the 3.3v power on signal over to the LED back light pin the back light would flash momentarily while there was no PWM to command the brightness.
Moving to the mainboard....
- Checked the electrolytic caps on the board. Each cap seemed to have an appropriate voltage except a few at the top left of the board. These rails seem to be powered on by a MOSFET near the power plug.
- Jumped the MOSFET to force it on. Other caps became hot but still no image.
- MediaTEK CPU was warm to the touch.
- Flash chip was seeing it's 3.3 volt rail like it should.
Maybe the firmware has become corrupted and no longer can boot?
Since a new mainboard is $28 including shipping I went ahead and ordered one. In fact the board I needed was not in stock so I went with one for a TV with a bigger screen and an additional HDMI port (PN: 3647-0812-0150). Once installed the TV is back up and running.
So here is a question... From a build quality standpoint what make/model TV would you purchase today? Or are all of these things just a throw away item these days?
Thanks,
A.J.