baird lcd tv no backlight

[shaunbt123]

Hi there to everyone,just wondering if someone can help me ,i have a baird 42 inch lcd tv model no-cn42bair.the green power light will come on as normal,however there is no backlight ,there is sound,i have tested the outputs on the power supply which are all giving out 0v except the 5v pin,but if i unplug the inverter board the voltages return to normal ie 12v and 24 v,also if i unplug the inverter i can see images on the screen with a torch. i cant see no bulging caps on power supply,i have tested the three caps on inverter board with esr meter all three were good.
thanks in advance.
shaun.

[tom66]

Re: baird lcd tv no backlight

Can you check across the inverter board capacitors for resistance, with the board unplugged? If the resistance is low, the inverter board probably has a short.

[shaunbt123]

Re: baird lcd tv no backlight

thanks for your reply. can you explain to me where i need to test for resistance ie where to put the test probes,sorry to sound dumb but as you can see im not an expert,i did test the caps with esr meter and it said they were ok.

[tom66]

Re: baird lcd tv no backlight

Set meter to 200 ohms (the horseshoe symbol if present.)

Across any one the caps on the inverters you tested, measure resistance. Power to the TV must be disconnected.

Report the reading you get.

[shaunbt123]

Re: baird lcd tv no backlight

thank you ill test the resistance of the caps later,ill get back to you later with the readings.thanks again.

[tom66]

Re: baird lcd tv no backlight

It's more of a test of the entire inverter rather than the caps.

[shaunbt123]

Re: baird lcd tv no backlight

hi again.with the meter on the 200 ohms setting, im getting the following
i tested all three resistors seperately and all show 0.62 ohms this is with the board disconnected from tv.
thx again for the help.

[tom66]

Re: baird lcd tv no backlight

Seems to be shorted. Just to be sure though, can you show me what range you had your meter on?

[shaunbt123]

Re: baird lcd tv no backlight

hi again heres a pic of the setting i had the meter on.

[tom66]

Re: baird lcd tv no backlight

That's the correct range. When you touch the probes together, what do you see?

[shaunbt123]

Re: baird lcd tv no backlight

if i touch probes together im getting
00.5

[tom66]

Re: baird lcd tv no backlight

And you get 00.62 or 00.6 or 06.2 across inverter? Just trying to figure out the extra digit.

[shaunbt123]

Re: baird lcd tv no backlight

ive checked again for you. heres the results
00.5 with probes together
04.2 across inverter
thx.

[tom66]

Re: baird lcd tv no backlight

4.2 ohms is definitely bad, does it rise or change at all?

[shaunbt123]

Re: baird lcd tv no backlight

it just stays at 4.2 ohms

[tom66]

Re: baird lcd tv no backlight

OK, so I would suggest either a repair or replacement of the inverter board. Repair would likely involve replacing all MOSFETs plus perhaps the driver IC and would cost around £15~£20 to do it yourself. Replacement prices vary.

[shaunbt123]

Re: baird lcd tv no backlight

i have found a replacement part for around £24 so im going to order that,when i have fitted it ,ill let you know what happens.
thank you again for your help.

[shaunbt123]

Re: baird lcd tv no backlight

Hi tom
just to update you.I got the new inverter board today and it worked a treat,i now have a fully working tv,so you were spot on when you said the old one was shorting out.
thanks very much for your help.
Just as a matter of interest what would the resistance across the caps have been if the board was ok.
shaun.

[tom66]

Re: baird lcd tv no backlight

Nearly infinite; >2kohm at the very least.
Glad to hear it's working!

[TVGUY101]

Re: baird lcd tv no backlight

heyyy can anyone tell me what is wrong with my tv please ????? all the colours have gone like this this morning and i need to replace what has gone wrong!! MAKE, Baird, MODEL, CN42BAIR