HP L1908w monitor - 2 second to black problem

[sententia]

Hello everyone,

I have these two HP L1908w monitor which went out after about two years of operation with same symptoms.

When the monitor is "cold" and has been off for some time, it will work for 5-10 minutes. After that it does 2 seconds to black....

I have seen a couple of threads in this forum with the same problem however i haven't come to a conclusion. I read about problematic connections to ccfls however the connections look good except that ccfls are a bit black at that side.

On the other hand i have found two capacitors on the power board (they are 1000uf 25v SAMXON CH, blue circle) that measure 900uf and 890uf with good ESR. Do you think they can cause the problem?

Any help greatly appreciated.
Thank you.

[1supertech]

Re: HP L1908w monitor - 2 second to black problem

Out of the two monitors you may be able to get two good test bulbs for testing

[selldoor]

Re: HP L1908w monitor - 2 second to black problem

Try and get a good pair of bulbs and check the board for bad joints.
Often decay on transformers and on the high voltage blue caps.

The centre joint on the mains connector doesnt look great.
Samxon caps are not good but if bulbs are shot nothing will help.
Can you hear any arcing from them?

[sententia]

Re: HP L1908w monitor - 2 second to black problem

Out of the two monitors you may be able to get two good test bulbs for testing

Is there any way to find out the condition of the ccfls? i don't have any other bulbs or power supplies as this is my very first attempt to repair a monitor. Reading through this thread https://www.badcaps.net/forum/showthread.php?p=231718
post 9, regarding same model monitors, i found that they say the top pair usually breaks. To me both pairs look the same with the same black spot on one side (see pictures).

Try and get a good pair of bulbs and check the board for bad joints.
Often decay on transformers and on the high voltage blue caps.

The centre joint on the mains connector doesnt look great.
Samxon caps are not good but if bulbs are shot nothing will help.
Can you hear any arcing from them?

The board does seem to have a lot of joints with oxidation starting on them. I don't know if that is the problem but i will revive some spots a bit. Is it possible that both monitors have the same problem? Also do you think the reduced capacitance of the 1000uf might cause the problem?
I don't understand what is "arcing" but i can definitely say that there is no sound coming from the monitors....

[budm]

Re: HP L1908w monitor - 2 second to black problem

You need to gently tug on the wire to see if it will come off (need to remove that KAPTON (yellow tape))
Test lamp: Make two of them.
https://www.badcaps.net/forum/showthread.php?t=19987

[sententia]

Re: HP L1908w monitor - 2 second to black problem

You need to gently tug on the wire to see if it will come off (need to remove that KAPTON (yellow tape))
Test lamp: Make two of them.
https://www.badcaps.net/forum/showthread.php?t=19987

Thanks for the link! .. Can the supply board of the 14w cfl be used to light also the monitor's ccfls?

I did remove the tape and checked the cables however they don't seem damaged at all and won't come off even with some force.

[budm]

Re: HP L1908w monitor - 2 second to black problem

"Can the supply board of the 14w cfl be used to light also the monitor's ccfls?" No.
It will save lots of troubleshooting time if we can narrow down the problem first to find out if it is the board or the lamps. I always use test lamps when I have 2-second to black problem to save my time.

[sententia]

Re: HP L1908w monitor - 2 second to black problem

"Can the supply board of the 14w cfl be used to light also the monitor's ccfls?" No.
It will save lots of troubleshooting time if we can narrow down the problem first to find out if it is the board or the lamps. I always use test lamps when I have 2-second to black problem to save my time.

Ok i will find some cfl to use them as test lamps. You are right it will be much easier and will save time.

Do all the ccfl slots have to be occupied for it to work?

Thanks!

[budm]

Re: HP L1908w monitor - 2 second to black problem

All the lamp sockets have to be connected, otherwise the sensing circuit will kick in and shut down the inverter circuits.

[sententia]

Re: HP L1908w monitor - 2 second to black problem

Hello,

Should i wait to receive the replacement caps? I have to find 4x cfls to test the inverter board...

Do you think the reduced capacity might be the problem? the 2x 1000uf 25V have 910uf and 890uf which maybe reduced as temperature rises.?

Also i read in the forum that many support that SAMXON are dodgy capacitors anyway...

P.S. I don't know if it matters but i checked the backlight hour counter and it has 5800 hours. The second monitor is the one i disassembled, but they had about the same usage and broke with 5 days difference.

[sententia]

Re: HP L1908w monitor - 2 second to black problem

Ok, after some more inspection, i noticed that the small black cable did come off after applying a bit more pressure. So i cut the second one as well, and connected two small 10mm long wires in order to keep the silicon terminal. Soldered those with the originals and covered with heat shrink.

The monitor has been working for 2 hours now without any problems!

I will post an update when i disassemble the second one.

Thank you!

[budm]

Re: HP L1908w monitor - 2 second to black problem

Good, just typical failure.
http://s807.photobucket.com/user/bud...tml?sort=3&o=6
http://s807.photobucket.com/user/bud...?sort=3&page=1

[sententia]

Re: HP L1908w monitor - 2 second to black problem

The second monitor had exactly the same thing. Top lamp, thin wire connection was loose!

It has been running for 3 hours now...

I tried to be as less invasive as possible. This time i did not rip off the second cable which had a good connection.

Thanks again everyone!

[selldoor]

Re: HP L1908w monitor - 2 second to black problem

Wow ! well done - two monitors fixed

[budm]

Re: HP L1908w monitor - 2 second to black problem

I think it is a must for people that want to repair the monitors to build test lamps for testing the board, it will save so much time every body times (hours) from troubleshooting the board that may not be the problem.

[sententia]

Re: HP L1908w monitor - 2 second to black problem

I think it is a must for people that want to repair the monitors to build test lamps for testing the board, it will save so much time every body times (hours) from troubleshooting the board that may not be the problem.

You are absolutely right.... With the first monitor i tested all electrolytics from power board and logic board before rechecking the lamps!

[sententia]

Re: HP L1908w monitor - 2 second to black problem

hello,
the monitors seem to have some kind of idol behind the image.

does it matter how the lamps cables are placed?

or maybe i did put the film sandwich the wrong way?

Thanks.

[budm]

Re: HP L1908w monitor - 2 second to black problem

Yes, may be the films are not back in the right sequence.

[int0x13]

Re: HP L1908w monitor - 2 second to black problem

Hello, i got one HP L1908W monitor i want to repair. It has the famous 2s to black symptom. First thing i want to check is the bulbs CCFL. For that i use an external inverter power supply, this one:
http://www.ebay.com/itm/CCFL-Inverte...item415e794728

I can plug 2 CCFL at once with this tester. There are 4 CCFL on this monitor. So ive tester the 2 top one and they light. And the bottom one light too. Ive tester the 4 one individually and they all light. It seems like in my case, the CCFL are all good, right?
Ive read all the topic about the 1907/8 2s to black, and it seems the most common problem is the 2 top CCFL connectors problem. but not seem to my problem. I have not my usual test bulbs at the moment. I just want to be absolutely sure that the CCFL in my monitor are good. If it lights with external inverter, does it mean its 100% sure they are good?
thanks.