Compaq WF1907 Turns On Then Off After Few Seconds

[Craigt4113]

Hello,

I am new to the forums and a beginner to electronics repair. I have a Compaq WF1907 19" LCD Monitor I picked up already broken. I opened it up and saw no visibly bad caps. I have replaced a few caps already but to no avail. I have the rest on order and should be here in the next few days. I am starting to think though from what I have been reading that it isn't so much the caps but maybe a transistor, transformer or maybe a CCFL. I am here to get some opinions on the matter from you guys. The power supply is marked as follows:

E59670
PTB-1808
6832180800P01

I have add a 2 pics of the board for visual reference.

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Sorry forgot to mention in the main body of the post that when it turns on there is an image for abotu 2-3 seconds then black while the green indicator light remains on. I also noticed that the top CCFL seems to be a bit dim.

Thank You,

Craig T

[PlainBill]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

The problem is called 'Two seconds to black'. The dim CCFL is an important clue. Inverters have protection circuitry which will shut down the inverter if the current through any CFL is too high, or if the voltage across any CCFL is too high (current too low).

One common failure is a bad solder joint at the CCFL, another is an aged CCFL.

Do you have any spare CCFLs available, or a 'test' monitor you can use for testing?

Another possible cause is shorted turns in the inverter transformer. Compare the resistance between the two terminals at each end. They should match to within 3%.

PlainBill

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Thank you for the quick reply, I have already checked and re-soldered both transformers on the board before I posted this, so that can probably scratch that off the list. Now when you say check the resistance of the end terminals do you mean the ones I have marked in red in the below attached picture? There are a total of 8 terminals on that transformer the other terminals I have marked in blue.

When you say a bad solder joint at the CCFL do you mean at the terminal on the board or where the wire meets the actual CCFL?

I do have another 19" different brand monitor I can test this on, I just hook up the CCFL's of the other one to this power supply correct and see if the lights stay on?

Thank You,
CraigT

[sabre504]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Where you have marked the trans in red ,
measure resistance between the top 2 pins then do the same on the bottom
2 pins and compare readings .

I would expect readings of 650 ohms and above and they should be within 3% of each other .

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

thank you sabre, I got 582 on the lower 2 in the pic and 581 on the top 2, so that doesn't see to be the problem

[sabre504]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Bit lower than expected but seems ok

[PlainBill]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Thank you for the quick reply, I have already checked and re-soldered both transformers on the board before I posted this, so that can probably scratch that off the list. Now when you say check the resistance of the end terminals do you mean the ones I have marked in red in the below attached picture? There are a total of 8 terminals on that transformer the other terminals I have marked in blue.

When you say a bad solder joint at the CCFL do you mean at the terminal on the board or where the wire meets the actual CCFL?

I do have another 19" different brand monitor I can test this on, I just hook up the CCFL's of the other one to this power supply correct and see if the lights stay on?

Thank You,
CraigT

Good news on the transformer.

The best approach at this point would be to hook the 'test' LCD panel to this power supply and see if the CCFLs stay on. If they do, that eliminates the inverter. After that, one at a time replace the test CCFLs with a CCFL from this panel. If you get 'two seconds to black' only when one of the top CCFLs from this panel is connected, you have identified the problem - it's either the wiring to the CCFL or the CCFL itself.

There are two leads going to each CCFL - Drive (the wire with thicker insulation) and return. Common problems include arcing through a hole in the insulation of the drive lead, arcing through the end support at the drive end of the CCFL, a failed solder joint at either end of the CCFL, and a frayed wire at either end.

PlainBill

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Thank you, I will give this a shot today and let you know what I find out.

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Ok so here is what I have found out so far, In the lower CCFL unit there is 1 dead unit and the top CCFL package both units are a pinkish color. I was unable to test the CCFL's in another rig cause I forgot I had shipped that one out already. So if one bulb is completely dead would that effect the rest? Any ideas where to go from here?

[PlainBill]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Ok so here is what I have found out so far, In the lower CCFL unit there is 1 dead unit and the top CCFL package both units are a pinkish color. I was unable to test the CCFL's in another rig cause I forgot I had shipped that one out already. So if one bulb is completely dead would that effect the rest? Any ideas where to go from here?

A total relamp may be required.

The protection circuits are detecting the open (dead) CCFL and shutting down the inverter. The pinkish color indicates the CCFLs are near their end of life.

PlainBill

[Craigt4113]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Thanks bill, I forgot I had a another LCD in the spare bedroom and I cracked that one open. I hooked up the CCFL's and same thing pink on 2 dead 1 and ok 1. So you are right I would have to do a total re-lamp and since I can not find these lamps I am going to part out the power supply and video board and e-bay it =). Thank you all who helped me on this I appreciate it very much and have learned alot.

[wesson]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Same problem ,. same monitor where is the CFL , i have my monitor taken apart and about to check the spots in red with my multimeter

[jayoung]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Same problem ,. same monitor where is the CFL , i have my monitor taken apart and about to check the spots in red with my multimeter

The spots in red are for testing the transformer secondaries.

The ccfl's are in the lcd panel, you have to take it apart to actually inspect / remove them.

[wesson]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

ok thank you very much

[eleazar_1812]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Hi I have a problem with an identical monitor is the same plate. My problem is that when connected directly to the power LED lights up and stays flashing, but not turn on or off. What could be the cause?

[Ober]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

I dont know anything about this problem, but if you hadnt already seen it, theres a Sticky about this subject at the top of this forum (Troubleshooting Computer Display section)

[selldoor]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Hi - Does you screen flash on at all - if not you are not really on the 2 seconds to black problem referred to by ober. There is still a lot of useful stuff in there, but you need to do other tests first.
We can help a lot more if you please post good clear pictures of the whole chassis, and then pictures of each board, front and back and close up of connectors, (max resolution 2000x2000 and 2MB) using the manage attachments button, which is found by clicking "go advanced" under quick reply.

Please do not post inline and offsite as they slow down the loading of pages.

Examples of what is needed
https://www.badcaps.net/forum/attach...1&d=1290283049

https://www.badcaps.net/forum/attach...7&d=1280167246

It will be useful if you can say a bit about yourself - skills tools etc.
Do you have a Multimeter and soldering equipment

[Napalm2002]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

Where can I find the replacement ccfl's? Are they cheap enough to buy and fix this monitor?

[stj]

Re: Compaq WF1907 Turns On Then Off After Few Seconds

http://stores.ebay.com/lcd-led-parts