Hitachi lcd tv L42VK04U not staying on

[thuss]

Hi

I am trying to repair this tv for my neighbour .
The red standby light is on.
I switch the tv on and the standby light flashes blue and backlights flash for a couple of seconds and then turn off.

Then the standby light justs cycles between red and blue.

The power supply is a vestel 17PW26-5 v.3.
The main board is a 17MB65-2.

I have replaced the inveter board and it does the same. Ive disconnected the inverter board but still the same.

On the power supply the white connecter top right hand corner I get the following voltages

Starting at the top with column on the left hand side
readings are

standby voltages /on voltages
0 / 0
7.86 / 8.97
2.57 /0
0.36
0 /3.57
11.86
5.03
3.39
0 /3.39
0 /3.39
0 /3.39
0
0.23
0.23

Power supply top right column nearest to main board


standyby voltage / on voltage
0
0
0
0
0.11
11.85
3.39
0 /5.15
0.24
0.24
0.1
0.28
0 /3.15


I have checked some of the caps on a meter and they are fine theres no leaks

Any pointers would be really appreciated -

[CapLeaker]

Re: Hitachi lcd tv L42VK04U not staying on

check the connector that goes to the inverter. looks like you don't have any 24V for the inverter on the PSU. First check the voltage on the main filter capacitor, in order to see if the PFC is running or not. If the PFC is running, check the rectifying diodes on the output section of the 24V rail.

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

Thanks- forgot to mention I am getting 24v from the top left connector block on the psu- on the inverter board fuse there is 24v. Ive checked the diodes they seem fine.

I will check the main filter cap

[CapLeaker]

Re: Hitachi lcd tv L42VK04U not staying on

Do the backlights come on at all?

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

Hi yes the back lights do come on for about 2 seconds.

Ive checked the fan chip seems fine high ohms,the smd caps surrounding the fan chip seem fine no shorts.

[CapLeaker]

Re: Hitachi lcd tv L42VK04U not staying on

compare the secondary windings on each HV transformer for the backlights. They have to be in line withing 3% of each other.

[budm]

Re: Hitachi lcd tv L42VK04U not staying on

Can we see the pcitures of the Inverter board without the metal shield?
What Voltages do you get on the connector of Inverter board that goes to the power supply board? Pin names for those pins?

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

As req With ref to the new attached photo of the connection wires that go from the psu to the inverter board.

Ive started with the green wire as number 1. (standby/ on voltage)


1 green wire on psu (standby /on voltages)- 0.6v/0
2 Pink wire 0/3.38
5 Brown wire 0/0
6 Brown wire 0/0
7 Brown wire 0/0
9 white wire 0.2/24
10 white wire 0.2/24
11 white wire 0.2/24
12 white wire 0.2/24


Ive have tried two inverter boards- still the same results

[R_J]

Re: Hitachi lcd tv L42VK04U not staying on

Try disconnecting one of the lamps from the inverter and see if the backlight still comes on for 2 sec. Then reconnect that lamp and disconnect the other lamp and try again. There may be a faulty ccfl

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

before I remove the lcd screen to get at the tubes- shouldn't the PSu have a constant 24v on the connector block from the main board.

[CapLeaker]

Re: Hitachi lcd tv L42VK04U not staying on

check these transformers first, before you take stuff apart.

[budm]

Re: Hitachi lcd tv L42VK04U not staying on

#1 green wire on psu (standby /on voltages)- 0.6v/0
#2 Pink wire 0/3.38

One of those two wire should be for BL-ON, another one will be for Dim control.'
The Voltage on #1 looks to be too low, you should keep the meter on that pin ten turn the TV on to see if it jumps up over 0.6V and then drops own to 0V or not, then try disconnecting just that wire #1 from the inverter board and see what Voltage you will get on that pin of the inverter board when you turn on the TV.

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

As req With ref to the new attached photo of the connection wires that go from the psu to the inverter board.

Ive started with the green wire as number 1. (standby/ on voltage)


1 green wire on psu (standby /on voltages)- 0.6v/0
2 Pink wire 0/3.38
5 Brown wire 0/0
6 Brown wire 0/0
7 Brown wire 0/0
9 white wire 0.2/24
10 white wire 0.2/24
11 white wire 0.2/24
12 white wire 0.2/24


Ive have tried two inverter boards- still the same results

My mistake the green wire has on standby 0.6v but today switched the TV on backlights came on for two seconds and the voltage went to 3.36v and then dropped

Cut the green wire same result as above just no backlights flash forgot to mention transformers seem fine

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

It's definitely the psu I repaired a 17pw26-5 (one main white plug)out of a toshiba that was lying about and the tv fires up fine- but not with the 17pw26-5(black and white plug)

[budm]

Re: Hitachi lcd tv L42VK04U not staying on

The control signals for the inverter are generated by the main board, they are just routed through the power supply board for neat wiring.

[thuss]

Re: Hitachi lcd tv L42VK04U not staying on

Just sourced another psu worked straight - couldn't work out what was wrong with original psu