HP w1907 LCD Monitor - white screen

[Rolin]

I have a HP w1907 LCD Monitor that powers up, but displays a blank white screen only. From my experience on Laptop repair, it's always the screen or the cable, but in rare cases it can be a motherboard issue. This appears to be a typical LCD screen failure.

The LCD monitor turns on and off OK. I checked several components on the logic board as well as the voltages coming off the power board - I believe everything looked OK from a basic standpoint. If you need this info in more detail, let me know. I researched the forums a litte and found a fuse can cause this on the LCD panel board. I found a fuse next to the connector and checked it - ohmed out to some stange reading, it's not 0, so it's open and bad.

I understand replacing the fuse probably won't solve the problem completely. What else should I check, or does the panel need to be replaced?

Attached are pictures!

Ideas appreciated!

[selldoor]

Re: HP w1907 LCD Monitor - white screen

Hi -Have you read this post www.badcaps.net/forum/showthread.php?t=18236
You probably need Momaka or another panel expert to help. As in the link I can only suggest you make sure the cable contacts are cleaned.

[retiredcaps]

Re: HP w1907 LCD Monitor - white screen

What else should I check, or does the panel need to be replaced?

See if IC3, a voltage regulator, is shorted or not. Number the pins 1, 2 and 3. Test for a short between pins 1-2, 1-3, and 2-3. Any reading under 30 ohms suggests a possible short and warrants desoldering and retesting out of circuit.

[PlainBill]

Re: HP w1907 LCD Monitor - white screen

In addition to the voltage regulator retiredcaps mentioned, there are a number of caps that are possible suspects. They are CD1, CD3, CD4, CD7, CD8, CD9, CD10, CD11. In addition, check SD1. And sometimes the fuse just blows.

PlainBill

[Rolin]

Re: HP w1907 LCD Monitor - white screen

IC3 doesn't appear to be shorted. Pins 1-2 is .624KOhms, 1-3 is 1.53KOhms, 2-3 is 2.2KOhms.

Plainbill, I checked all the caps you mentioned for shorts - none were shorted. I don't know how to really checks caps to see if they're in spec, but they don't appear to be shorted.

Don't know how to check SD1 - I metered the leads a little and there are no shorts I guess.

Could I be one of the lucky ones where this is only a fuse? I have no idea how to find the value for this fuse, and I'm a little afraid to jump accross it - unless you guys think it's OK to try!

[Rolin]

Re: HP w1907 LCD Monitor - white screen

Selldoor, I did read that thread and the youtube link. Interesting how common it's needed on one particular model.

I've reseated connectors on LCD screens in laptops often - it's the first thing I try. It does work sometimes. If a reseat works, I usually will clean with alcohol or use the eraser trick. I learned the eraser trick at Control Data and Unisys back in the 80's - very common fix back then on larger computer equipment with lots of boards! The board contacts needed cleaning much more often back then for some reason - I don't think they used gold contacts as much or something like that.. don't remember why exactly. It's a good trick on cheaper RAM modules too!

[selldoor]

Re: HP w1907 LCD Monitor - white screen

I have been looking for a fuse value but failed. I see Tom66 soldered his over but blew other components. I have heard of others trying a very thin wire then if it did work start with a low amp and work up. Some solder in a fuse holder to make use of cheaper fuses. I might even have read of someone using a light bulb but not sure about that. Ill see if I can find it.
In looking I did see that someone with white screen had decided it was a transistor on the video board but unfortunately didnt say which and didnt confirm it. going on from that if you can post a better pic of your video board we may be able to spot a burn or others may suggest which transistors could cause white screen. Q302? I301?
I have what I think is the schematic and that might help.

[retiredcaps]

Re: HP w1907 LCD Monitor - white screen

I have no idea how to find the value for this fuse, and I'm a little afraid to jump accross it - unless you guys think it's OK to try!

Your photo resolution is a bit low, but I think I can see a letter on F1. The letter will tell you the fuse amperage required.

[Rolin]

Re: HP w1907 LCD Monitor - white screen

Update:

Selldoor, I'm pretty sure I also read somewhere that someone used a light bulb in place of the fuse -If it lights, then you have a short somewhere! I can understand how it could work, but I've never tried it! Thanks for finding those schematics - but in the end I didn't need them.

RetiredCaps, it's a "k" for 1.5 amp. I have some old laptop LCDs laying around with cracked screens, etc - I use them to test for backlight issues on laptops like I've read you do as well. Anyway, I found a "k" on one of them! Surfacemount soldering is tricky, but I managed to remove the old one and solder in the new one. The darn thing works. I can't believe it was such an easy fix - a little fuse on the LCD panel. This was a fairly nice monitor a few years ago, and quite frankly it still is very very nice - great picture. It's been sitting around for at least 3 or 4 years until I finally "got around to it".

Thanks for the help guys. I'm on to the next one!

[retiredcaps]

Re: HP w1907 LCD Monitor - white screen

Selldoor, I'm pretty sure I also read somewhere that someone used a light bulb in place of the fuse -If it lights, then you have a short somewhere! I can understand how it could work, but I've never tried it!

http://www.repairfaq.org/samnew/tvfaq/tvtslbt.htm

[Demo-Enterprise]

Re: HP w1907 LCD Monitor - white screen

its the fuse on the lcd.....F101 and FL101