HP LA1905WG lcd monitor no backlight

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

today..i did find a good working board and so far the transformer reading of 2 pins and mosfet reading are all the same among the 3bad boards and 1 known good one

so need new direction...

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

i was going to try to swap transformers to see if thats the issue but cant get it off....lead free solder on both sides board......my novice desolder iron not able to remove....was going to try to cut legs off with dremel.....any ideas?

cant i test trans in circuit to make sure they are good?

[stj]

Re: HP LA1905WG lcd monitor no backlight

even if both are bad, the chances of them reading exactly the same are very slim.
if you get the same readings from both then they are probably o.k.

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

yes same exact reading on the end with 2 pins...on all 4..boards......what the heck could be causing the issue...it must be common....i have 4 of these doing exact same thing......backlight on then off after 3seconds

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

i have 1 good board.....and the trans had same readings as the bad boards

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

hi....update

the power supplies are good....it must be a backlight/wiring issue....

i had in my notes that i tested backlights and were good but today i took all the ps and installed in the known good monitor and they all worked....i then installed the known good ps in the other non work ones and the backlight went off after few sec.....so yes the bad monitors all have an issue with backlight or shorted wires or someting in the blight.....

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

thanks bud m and to all others who responded to my thread......since it seems to be a backlight circuitry issue i will toss them out and sell the boards on ebay and maybe try to sell the lcd displays?.....im sure i can sell the boards but kinda doubt the lcd displays would sell

[stj]

Re: HP LA1905WG lcd monitor no backlight

or buy some led kits for about $15

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

what do u mean led kits?.......monitors not worth repairing if more than 5.00 in parts

[stj]

Re: HP LA1905WG lcd monitor no backlight

maybe not for selling, but for personal use it would be worth $10-15 easy.
those are nice monitors.

led kits:
http://stores.ebay.com/lcd-led-parts...sub=5733816011

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

nah...i have over 40 lcd monitors now....i try to fix them just to learn......ill make more money sling the boards on ebay....

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

yes they are good monitors..not cheap.....we use them at work.....they throw them away and i take them and fix sometimed....if cracked screen i convert them into work lights .....the led ones are nice n bright i have 3 above my work bench.....very bright

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

the stands on these monitors are real nice...made of metal frame not cheap plastic.....i have 20 of them

[stj]

Re: HP LA1905WG lcd monitor no backlight

is that the stand with the 90' rotation function they used on the 1740/1940?
those are fantastic!

[budm]

Re: HP LA1905WG lcd monitor no backlight

So the lamps are bad.
I am curious as how you went about testing the lamps before?

[stj]

Re: HP LA1905WG lcd monitor no backlight

testing with a cheap invertor for driving pc illumination probably, those dont have overcurrent sensing.

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

yep....the stands are nice built and look nice and rotate 90 and adjust up down....i basically have a lot of these csuse at work they mount monitors with no stand do i get the stands now n then

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

i tested the lamps by taking a simar model monitor back then and had both backs off and just plugged the backlight power cables from suspect monitor into the other monitor ps snd the backlight stayed on.....

[shelby5041]

Re: HP LA1905WG lcd monitor no backlight

im going to do some further testing...maybe there is some wire issue....but yes the problem is in the backlight circuit....if i tap the back of monitor real hard the backlihht comes on for 1 sec then off.....and i can repeat it over n over

[budm]

Re: HP LA1905WG lcd monitor no backlight

Bad CCFL, bad wiring:
http://s807.photobucket.com/user/bud...?sort=3&page=1