LG FLATRON W2042TQ-BF. blue led - no display

[benV]

Hi Everyone. As you can see, it's my firts post. I'm from Montreal, Canada and i'm french so my english isn't top notch.

I have 3 of these monitors, all from the same IT company and all with the same symptom. First of all, as you can see on the picture of the power board i replaced all the big caps (that were bulged or burts) with nice and new Panasonic FC series from digikey.

So, the blue led lights perfectly when i push the power button but then, i heard a "buzz" coming from the inverter (the big chip near the ccfl sockets). I measure the voltage at the power board exit to the logic board and everythings seems ok (the connector at the lower right corner of the power board). I tried to plug others ccfl to see if it was the problem, but they "buzz light" a little bit in rythm with the inverter and then nothing.

I was not able to find the service manual for this specified LG monitor. The power board is a 03V0-B94V-0.

Thanks in advance for your help and i hope my explanation is clear

[retiredcaps]

Re: LG FLATRON W2042TQ-BF. blue led - no display

1) Those are excellent focused pictures.

2) Do the ccfls come on at all, even briefly?

3) Check U303 and U304 (backside) to see if the mosfets are shorted or not. Datasheet is at

http://www.alldatasheet.com/datashee...525GEH_08.html

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

1) Thank you.

2) just the tips of the ccfl with a dim light during the short buzz.

3) I've never check mosfet before so, here is what i'v done : testing in diode mode with my multimeter

- on S1, + on G1 : nothing
- on S2, + on G2 : 0.001 v
- on S1, + on D1/D2 : voltage increase a little bit then nothing
- on G1, + on D1/D2 : nothing
- on S2, + on D1/D2 : 0.000 v
- on G2, + on D1/D2 : 0.001 v

Same result for U303 and U304. Does this mean anything for you ?

[jetadm123]

Re: LG FLATRON W2042TQ-BF. blue led - no display

1) Thank you.

2) just the tips of the ccfl with a dim light during the short buzz.

3) I've never check mosfet before so, here is what i'v done : testing in diode mode with my multimeter

- on S1, + on G1 : nothing
- on S2, + on G2 : 0.001 v
- on S1, + on D1/D2 : voltage increase a little bit then nothing
- on G1, + on D1/D2 : nothing
- on S2, + on D1/D2 : 0.000 v
- on G2, + on D1/D2 : 0.001 v

Same result for U303 and U304. Does this mean anything for you ?

Let's try testing them a little differently:

With power OFF and your meter set to 2k ohms resistance setting, measure across the following pins of U303:

G1 and S1
G1 and D1/D2
S1 and D1/D2
G2 and S2
G2 and D1/D2
S2 and D1/D2

do the same for U304 and post your results.

--------------------------------------------------------------------------------

[jetadm123]

Re: LG FLATRON W2042TQ-BF. blue led - no display

It also looks like the inverter transformer, T301, has been running hot. T301 is located on the left side of your first photo. Again, with power OFF and your meter set to 2kohm resistance, measure across the two secondaries on T301. The secondaries consist of 2 pairs of pins (total 4 pins) on the side of the transformer closest to the ccfl sockets. Measure across each pair of pins. There should be no more than 3% difference between the measurements.

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

Let's try testing them a little differently:

With power OFF and your meter set to 2k ohms resistance setting, measure across the following pins of U303:

G1 and S1
G1 and D1/D2
S1 and D1/D2
G2 and S2
G2 and D1/D2
S2 and D1/D2

do the same for U304 and post your results.

--------------------------------------------------------------------------------

Hope i made no mistake this time:

U303 - U304
open - open
open - open
open - open
3.4 - 3.4
3.4 - 3.4
0.3 - 0.4

Sounds good ?

[retiredcaps]

Re: LG FLATRON W2042TQ-BF. blue led - no display

Hope i made no mistake this time:

U303 - U304
open - open
open - open
open - open
3.4 - 3.4
3.4 - 3.4
0.3 - 0.4

Sounds good ?

You should have 6 measurements for each mosfet for a total of 12. If you are saying both measure the same above, then you had two bad mosfets. In particular, the S2, G2, and D2 are all shorted.

edit: Desolder both and measure out of circuit to verify.

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

You should have 6 measurements for each mosfet for a total of 12. If you are saying both measure the same above, then you had two bad mosfets. In particular, the S2, G2, and D2 are all shorted.

edit: Desolder both and measure out of circuit to verify.

Ok. I'll do it and i'll also test the two other monitors to see if i've got the same readings.

If those mosfet are dead, where can i find replacement ? Nothing on Digikey's website. And if they are dead, is it possible that they kill other parts when they died. Just to know if it worth the not so easy fix.

Thanks.

[selldoor]

Re: LG FLATRON W2042TQ-BF. blue led - no display

It also looks like the inverter transformer, T301, has been running hot. T301 is located on the left side of your first photo. Again, with power OFF and your meter set to 2kohm resistance, measure across the two secondaries on T301. The secondaries consist of 2 pairs of pins (total 4 pins) on the side of the transformer closest to the ccfl sockets. Measure across each pair of pins. There should be no more than 3% difference between the measurements.

I have just fixed an lg W2042S which seems to have the same board as this
I would go for doing the above tests before anything else. My transformer was borderline on the 3% - I had already recapped it without testing anything.
Just left it for months as I couldnt decide whether to go for a new board or try a transformer. Transformer price reduced from around £5 to £3.50 so worth a punt. A bit of a wait from china but fitted and it works fine.
I got it from here http://www.ebay.co.uk/sch/monitor-09....c0.m270.l1313 Doesn't mention 2042 in the add but it is an eel22 Mine was originally an EEL22d - Not sure what the D means probably slightly different resistances.

Pic added - you may need to scratch lacquer off pins to test resistance

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

I have just fixed an lg W2042S which seems to have the same board as this
I would go for doing the above tests before anything else. My transformer was borderline on the 3% - I had already recapped it without testing anything.
Just left it for months as I couldnt decide whether to go for a new board or try a transformer. Transformer price reduced from around £5 to £3.50 so worth a punt. A bit of a wait from china but fitted and it works fine.
I got it from here http://www.ebay.co.uk/sch/monitor-09....c0.m270.l1313 Doesn't mention 2042 in the add but it is an eel22 Mine was originally an EEL22d - Not sure what the D means probably slightly different resistances.

Pic added - you may need to scratch lacquer off pins to test resistance

Here are the results:

0.978 on one side and 0.970 on the other side. This means that the transformer is good, isn't it ?

[PlainBill]

Re: LG FLATRON W2042TQ-BF. blue led - no display

Here are the results:

0.978 on one side and 0.970 on the other side. This means that the transformer is good, isn't it ?

Probably - that's 1% difference. I consider anything below 3% to be good.

PlainBill

[selldoor]

Re: LG FLATRON W2042TQ-BF. blue led - no display

It was worth trying - easier than desoldering mosfets.

So, the blue led lights perfectly when i push the power button

Does the light stay on blue? flash? Orange?

If you set it up with a computer with vivid desktop page can you make out
anything on the screen using a torch or bright light source.

I tried to plug others ccfl to see if it was the problem, but they "buzz light" a little bit in rythm with the inverter and then nothing.

Did you have a full set of ccfls plugged in ?

What did you mean by this " I tried to plug others ccfl " do you mean a panel from one of the other two monitors.

Can you try one ccfl at a time into each socket and note down any differences. - it wont stay lit but one might not do anything one might light the full tube, one might just light at the very end etc. Also record if the buzz occurs the same as well.

[selldoor]

Re: LG FLATRON W2042TQ-BF. blue led - no display

If those mosfet are dead, where can i find replacement ? Nothing on Digikey's website. And if they are dead, is it possible that they kill other parts when they died. Just to know if it worth the not so easy fix.
Thanks.

Dont know about killing other parts but similar items are available perhaps
FDD8424H would be a substitute - have to ask retiredcaps.

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

It was worth trying - easier than desoldering mosfets.



Does the light stay on blue? flash? Orange?

If you set it up with a computer with vivid desktop page can you make out
anything on the screen using a torch or bright light source.



Did you have a full set of ccfls plugged in ?

What did you mean by this " I tried to plug others ccfl " do you mean a panel from one of the other two monitors.

Can you try one ccfl at a time into each socket and note down any differences. - it wont stay lit but one might not do anything one might light the full tube, one might just light at the very end etc. Also record if the buzz occurs the same as well.

1 - The light doesn't stay. It doesn't even full light at all ! I will try the torch on the panel to see if something is hidden underneath.

2 - Yes i had a full set of ccfls plugged in. I tried two different sets i got and i know they are ok. They were pulled from dead monitors and tested. I already used them to troubleshoot dead ccfl on others monitors.

[selldoor]

Re: LG FLATRON W2042TQ-BF. blue led - no display

"So, the blue led lights perfectly when i push the power button "

Imeant this blue light

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

"So, the blue led lights perfectly when i push the power button "

Imeant this blue light

Ok, sorry . Yes, this blue light stay rock solid on. No flickering, blinking,or whatever else.

[retiredcaps]

Re: LG FLATRON W2042TQ-BF. blue led - no display

Dont know about killing other parts but similar items are available perhaps
FDD8424H would be a substitute - have to ask retiredcaps.

ebay has the AP4525 mosfet ($1.49 each) at

http://www.ebay.ca/itm/150727448104

Shipping to Canada is a reasonable $6.49 from Florida considering Digi-key will charge $8 for s/h. You might want to order 4 instead of 2 incase the mosfets blow again or a soldering mishap. Each extra AP4525 is shipped free.

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

You should have 6 measurements for each mosfet for a total of 12. If you are saying both measure the same above, then you had two bad mosfets. In particular, the S2, G2, and D2 are all shorted.

edit: Desolder both and measure out of circuit to verify.

I desoldered both and here is the result:

U303-----U304
open-----open
open-----open
open-----open
3.4------open
3.5------open
0.3------open

Does this mean that only U303 is shorted ? Both mosfet were plugged in parallel on the circuit. Is it the reason that i had the same result on both of them before?

I found a chinese website that sell AP4525GEH :

http://www.aliexpress.com/store/4030...e-shiping.html

Does anyone of you ever use their service ? Feedback someone ? Thanks again.

[retiredcaps]

Re: LG FLATRON W2042TQ-BF. blue led - no display

I desoldered both and here is the result:

U303-----U304
open-----open
open-----open
open-----open
3.4------open
3.5------open
0.3------open

Does this mean that only U303 is shorted ? Both mosfet were plugged in parallel on the circuit. Is it the reason that i had the same result on both of them before?

Yes, only U303 is shorted, but we recommend replacing both since U304 may be stressed as well.

I found a chinese website that sell AP4525GEH :

http://www.aliexpress.com/store/4030...e-shiping.html

Does anyone of you ever use their service ?

No.

[benV]

Re: LG FLATRON W2042TQ-BF. blue led - no display

First of all, i want to thank you all for your precious help

I bought 10 AP4525GEH on the site from the link i posted before and after i received those precious mosfets from the other side of the world, i tried to put two of them back at the place they are supposed to be on my first monitor and ...drum roll... the Flatron W2042TQ is back on earth ...hallelujah !

As you can see, i'm quite happy of my first "something else than a capacitor" soldering success.

There's two more monitor on the shelf to resurrect, with same symptom (shorted Mosfets), and all i have to do is to improve my desoldering abilities.

Thanks again.