Hitachi cmp4121hdu 42in plasma tv turn the main power switch on (indicating lamp is red), turn the power on (green) and black screen can't turn off, stays (green) with black screen, no more control on the adjustment buttons. need to turn the main power switch off/on (red) POWER SUPPLY???

Main board is possible but power supply board should first be tested.

Nope. It appears that you now have a main power supply issue since the set is dead.

Do you hear sound? If not, check the input cable, cable connector etc for possible loose contacts. If these are ok, there is a power supply failure or secondary power failure inside the TV and might require an expert to look in.

First do you see a light indicating that the TV has power? There are two power buttons on the TV (the main power and the regular power button). The red standby light will light up when the main power switch is on. This indicator is just to the left of the remote I/R sensor. You can find the main switch on the bottom front of the tv (it is under the tv forward of the stand). Turn on the Main power if it is not on. Then try the power button on the control panel of the TV again.

Does the standby light change color or blink? (Red is standby, orange is power savings (no signal), blue is on.) If the main switch is on and the standby light doesn't come on, the TV has a problem at the power supply. Try unplugging the unit for a bit (at least 30 seconds) and then plugging it back in. This will reset the internal circuitry. If you see a blinking light, then the TV is reporting a self-test failure. I do not know the codes for this model Hitachi Plasma TV.

The manual for the Hitachi P50H401 TV is available from Retrevo: http://www.retrevo.com/support/Hitachi-P50H401-TVs-manual/id/1233ci869/t/2/ . You will need to enter a code to access the pdf.

I'm assuming you don't have one of the special versions that were intended for large audiences that were only controlled by remote (no control keys on the front of the TV). Remotes.com has the original remote or a substitute remote if you need it. See http://www.remotes.com/remotes/servlet/rs?a=gmi&uuid=13104063628240&smodel=P50H401&brand_pn=HITACHI_P50H401 .

I hope this helps.

Cindy Wells

It's most likely the smps. You'll first need to check voltages at CN63, pin #1-(+5v), 3-(+3.3v) and pin 8-(+6v) Also check CNPPS, pin 1-(+30v), 4-(+5v), 8-(+12v), 12-(+10v) absent these values and the power supply is clearly the problem.

I would open back and check all boards for cracks, this is a problem with these sets.Then count the blinks on the set and see if it stops for a moment and starts back.

I've had the same problem. (black vertical lines) They will appear then go away. I have a 42EDT41 42in. Now my screen has gone completely Black.

Y sus (sustain) board or main power board has dry capacitors or dead transistors or even main chip is dead, but to know more accurately you need to count the red light flashes. Google "red blinking codes" should find the answer, ebay sells Y sus boards or power boards around $125 (cheapest) for plasma TVs.

unplug unit for 1 minute turn off main power button plug in then press main power button and try!

the cooling fan could be going out