HP L1955 no display following wake from sleep

[dimsim]

One of my L1955 monitors has just started to not wake up from power save or sleep. I have been able until now to simply either switch off or remove the power cable then re-power which will make it work again until the next power save or sleep time. The green power led lights all the time (dims slightly when the display appears) then the backlight appear to turn off and the power led stay on. It now also just perodically dies, still with the green led lit with text visible by torch.

I had another one which totally burnt something out on the power board (see attached P107490) and i swapped the power board out of a working display into that and it worked perfectly. I've since swapped the power board from this one into that and get the same problem so assume it is something wrong with that board and not anything else.

Does anyone have any ideas where i should start? The CAPS as far as I can see are ok.

Photos of boards attached.

[leekh]

Re: HP L1955 no display following wake from sleep

replace all the brown and green caps on the power board. both of these brands are known to give problems.

[dondrusco]

Re: HP L1955 no display following wake from sleep

I had another one which totally burnt something out on the power board (see attached P107490) and i swapped the power board out of a working display into that and it worked perfectly. I've since swapped the power board from this one into that and get the same problem so assume it is something wrong with that board and not anything else.

Burned c5707 is common problem of Benq power boards due to cold joint

https://www.badcaps.net/forum/showthread.php?t=6692

[kc8adu]

Re: HP L1955 no display following wake from sleep

looks like the 5707's burned or the cap in between them.
some of those plastic box caps were trouble too.
but most blowups in these is brought on by bad solder joints on the ccfl transformers and the 5707's

[dimsim]

Re: HP L1955 no display following wake from sleep

looks like the 5707's burned or the cap in between them.
some of those plastic box caps were trouble too.
but most blowups in these is brought on by bad solder joints on the ccfl transformers and the 5707's

Wow! Thanks for everyones input, these boards really have issues then huh.

Last nite following another switch on/off I got the burning smell and a puff of smoke, I quickly removed the power, disassembled and found the C5707s on Q808 & Q809, the R75 MKP on C824 and the D10pf on Q805 all with some kind of heat damage. The D10pf on Q812 also looks like its had some heat so I guess its just a matter of time until that goes along with the 5707's on Q815 & Q816 & the R75 MKP on C825

On the previous board that had failed and had a major burn out right through the PCB it was Q808/9, Q805 & C824, so same fault, but others have mentioned that Q815/6 have failed on them.

So to sum up, it would appear that I should

Replace the 2x D10pf at Q805/Q812
Replace the 4X C5707 at Q808/9 & Q815/6
Replace the 2X R75 MKP at C824/5
Resolder the 9 joints on T801/2/3/4
and
Replace all the brown and green caps?

Sounds like a lot of work huh? Especially for a newb like me.

If I do all this does anyone know if anything else is likely fail?

Also any recommendations for the replacement components?

[Bobdee]

Re: HP L1955 no display following wake from sleep

Possibly Inverter transformer damage after that burn up
I would add to your list C801+c802, also a few PF701 fuses as the one on your board is no doubt open
Resolder all four of the Inverter transformers, and check the whole board for bad solder cracks etc

[dondrusco]

Re: HP L1955 no display following wake from sleep

Possibly Inverter transformer damage after that burn up
I would add to your list C801+c802, also a few PF701 fuses as the one on your board is no doubt open
Resolder all four of the Inverter transformers, and check the whole board for bad solder cracks etc

Q805, Q812 - be careful, they are MOSFETs - sensitive to static electricity.
I damaged them during resoldering

[nickBcap]

Re: HP L1955 no display following wake from sleep

Hi, dimsim - have you an idea as to what the burning smell may have been. I found no evidence of burning anywhere and guessed it would be a capacitor from my short experience. But no capacitors are bulging and no burn marks anywhere. Maybe there is slight browning somewhere.

I bought an HP L1955 for NZ$44 and it worked ok for about one week and turned it on one day and smelled an unusual burning smell. Turned the monitor off very quickly and now wondering would replacing the 13 capacitors on the power board get it working again?
I can remove all those capacitors and identify them and buy replacements but will it work? Maybe I got to turn it off before any major damage occurred.

[Rtech]

Re: HP L1955 no display following wake from sleep

There used to be a tongue in cheek method of fault finding which was 'Tune for maximum smoke',and although I am not a supporter of doing that,the information you give does not help to pinpoint the problem.You need to connect Computer and Monitor as normal, apply power, advise how the Power Led reacts,ie comes on,changes colour. stays steady etc etc, what is going on with the screen, if anything ?

[nickBcap]

Re: HP L1955 no display following wake from sleep

When I plug the monitor in and power it on the power LED on the front panel lights and does not change until I press the AUTO button and then it lights brighter, perhaps it lights green, but brighter, and nothing changes on the screen, the screen remains black.
When I was first using the monitor it worked very well and I played first person shooter online games with the monitor.

[Rtech]

Re: HP L1955 no display following wake from sleep

If you have a PC connected to it,why press auto??the Monitor should pick up the PC signal and the Led should change colour to confirm the Monitor has recognised it.As far as I am aware.all of the Monitors/TVs etc Have dealt with have had this facility.The performance of the Led is the first step in trying to find a place to start fault finding.