HP W2207 Backlight Problem

[pedro]

Re: HP W2207 Backlight Problem

They are Su'scon... Damn, I really wish I had an ESR meter. Can't justify it quite yet.

There are only two paths available - commit to buy an ESR meter, or replace all (*) suss-branded caps on sight. Shotgunning the caps is cheaper, but eventually (if you keep doing this type of repair) the ESR meter will pay its way into your toolbox.

What about that big fatty Cap?

Those rarely fail. Not never, but rarely. If your line voltage is 110/120 and not 230/240 then they are not subject to voltage stress anywhere near their limits, and they normally don't see huge heating.

[TVo]

Re: HP W2207 Backlight Problem

Hey, sorry about the delay. I finally measured the ohms of the locations you highlighted. I have my device set to 200k and was unable to get ANY reading. I even tried 20M and only got 0.00 on both.

[retiredcaps]

Re: HP W2207 Backlight Problem

I even tried 20M and only got 0.00 on both.

Use 2000 ohms (as per post #18).

[PlainBill]

Re: HP W2207 Backlight Problem

Hey, sorry about the delay. I finally measured the ohms of the locations you highlighted. I have my device set to 200k and was unable to get ANY reading. I even tried 20M and only got 0.00 on both.

0.00 IS a reading on a resistance measurement. It means 'too low to measure'. OL or the equivalent (varies with the meter) is 'no connection', two vastly different things.

PlainBill

[alexanna]

Re: HP W2207 Backlight Problem

Hey, sorry about the delay. I finally measured the ohms of the locations you highlighted. I have my device set to 200k and was unable to get ANY reading. I even tried 20M and only got 0.00 on both.

I just picked up one of these today. It has 2 bad CCFL's.If you need to compare any readings let me know.

[TVo]

Re: HP W2207 Backlight Problem

Sorry I keep dragging this out. It's been a while since I've been able work on this again. I'm attaching a picture of my multimeter in hopes that someone can tell me which setting to use. When I measured it using the circled settings shown in the picture I didn't get a very good reading.

Thanks if anyone can tell me what to set it to to measure the inverter.

[retiredcaps]

Re: HP W2207 Backlight Problem

Thanks if anyone can tell me what to set it to to measure the inverter.

Most secondary inverter transformer readings are around 1000 ohms or 1K. With your multimeter set to 200K, that would mean the reading should show up as 1 on the right hand side of the display. A reading of 1K will probably not be sufficient resolution to tell if your transformer is good or bad.

In order to do this test, you will need to borrow a multimeter that is autoranging or a manual one with a 2000 ohm range.

PS. Most manual range multimeters have ohms ranges of 200 ohms, 2k, 20k, 200k, 2M, and 20M. I can't recall seeing one like yours with such a wide gap in the ohms range. I suspect it was to allow the MFD range so they had to compromise.

[TVo]

Re: HP W2207 Backlight Problem

Awesome! Thanks for the reply. I'll see if I can't find a meter with the 2000 range.

[retiredcaps]

Re: HP W2207 Backlight Problem

I was in the hvac-talk.com forum and saw reference to your multimeter, Field Piece.

Looks like it is a fairly specialized meter and thus doesn't have the same ranges like electronic multimeters.

[TVo]

Re: HP W2207 Backlight Problem

Resurrecting this thread yet again!

Ok, so I picked up an inexpensive DMM that can measure at the 2k range. Here are my findings:

As per retiredcaps instructions here:

Linky

I measured the red circles:

.478

and the yellow circles:

.484

That looks to be within the 3% threshold.

Now, some more info. I have about 10 monitors I received since my company does recycling. All of the monitors have a 3 second to black problem. Of the three monitors I have so far opened, ALL THREE HAVE THE SAME POWER BOARD.

I replaced ALL the caps on the powerboard pictured above on my first post. None of the caps were distorted at all, and with the cheap capacitor tester I recently purchased (which could be crap, but here is a link) said that the caps were mostly in the correct range. Granted, it's not ESR and it doesn't rule much out, but I was able to replace all the caps anyway.

After reading many posts about this board (it's fairly common and the actual LCD manufacturer seems to be Samsung for these 3 monitors I opened up with the same problem) I decided to set up a test CCFL. I had ordered some new CCFLs a while back so I rigged one up to connect to the board. Brand new CCFLS! I tried testing each board and the SAME problem showed up:

When the board powers up, the CCFL lights up dully (not a full light up) for about 2 seconds then shuts off. I have tried this with 3 of the brand new lights to the same effect.

I will not let this thing beat me! Especially since I have 3 different boards, if I could even get ONE to work I would be happy. I have a feel it's a similar problem, and I have found others with the same board with the same symptoms and the fact that I have THREE of the SAME boards makes me want to fix this like crazy.

The next step:

I read somewhere that someone was having problems with the mosfet or something like that. Should I give that a test?

Thanks for all the help! I'll try to buy everyone a round of beers when/if I can fix this thing!

[alexanna]

Re: HP W2207 Backlight Problem

^
When you're doing the testing you do have 4 CCFLs installed correct?

[TVo]

Re: HP W2207 Backlight Problem

No, only the one. Should I plug in all 4?

[alexanna]

Re: HP W2207 Backlight Problem

Yes they all need to be installed

I would use 2 new in one tranformer and 2 old in the other,then switch every thing around if the second to black problem continues.

[jetadm123]

Re: HP W2207 Backlight Problem

Resurrecting this thread yet again!

The next step:

I read somewhere that someone was having problems with the mosfet or something like that. Should I give that a test?

Thanks for all the help! I'll try to buy everyone a round of beers when/if I can fix this thing!

Looks like you checked the two most likely suspects: the transformers and the CCFL's.

If your board is the same as in post #1, then go ahead and check U501 and U502 for shorts. What are their part numbers?

[alexanna]

Re: HP W2207 Backlight Problem

Looks like you checked the two most likely suspects: the transformers and the CCFL's.

If your board is the same as in post #1, then go ahead and check U501 and U502 for shorts. What are their part numbers?

I don't know for sure on this model, But some of the monitors with a transformer for a pair of CCFLs
Require that 2 CCFLs be installed, If only one CCFL is used the lamp will only light part of the way.
I would redo the test with all the CCFLs installed

[retiredcaps]

Re: HP W2207 Backlight Problem

I measured the red circles:

.478

and the yellow circles:

.484

That looks to be within the 3% threshold.

Those readings suggest the inverter transformer is likely good.

with the cheap capacitor tester I recently purchased

For $30, you could have potentially gotten a used Fluke 12 which is a great multimeter and it measures caps up to 9999uF. The Fluke 12 will not measure ESR though.

I had ordered some new CCFLs a while back so I rigged one up to connect to the board. Brand new CCFLS! I tried testing each board and the SAME problem showed up:

Here is how I suggest testing your ccfls. See this #5 at

https://www.badcaps.net/forum/showpo...1&postcount=14

[PlainBill]

Re: HP W2207 Backlight Problem

I don't know for sure on this model, But some of the monitors with a transformer for a pair of CCFLs
Require that 2 CCFLs be installed, If only one CCFL is used the lamp will only light part of the way.
I would redo the test with all the CCFLs installed

Correct. Some designs have the CCFLs in parallel, others have them in series with the current sense circuitry at the junction. This board uses the series design.

PlainBill

[TVo]

Re: HP W2207 Backlight Problem

I don't want to jynx it but I think that was it! I'm putting everything back together now (it's been so long that I don't actually remember how the LCD panel goes anymore...) and I'll report back when done!

Thanks for the help! You may have just saved me hours and hours!

[retiredcaps]

Re: HP W2207 Backlight Problem

I don't want to jynx it but I think that was it!

What was "it"?

[TVo]

Re: HP W2207 Backlight Problem

What was "it"?

"it" was plugging in all 4 CCFLs instead of just one good working one.

I spoke too soon, however, as when I finally started getting the internals placed back inside the LCD case, I tested again and back to the 2 seconds! Yeesh. I'll never get this thing fixed.

Taking it apart again to make sure all my joints are looking good.