Dell 5590 no image on LCD,HDMI works ,the board works...

[huzo]

The board is LA-F411P ,DELL 5590 ...

The screen polarises,no backlight,no image,only black screen,tried another screen,the same,so there is no backlight,but there should be an image when i shine a lamp behind the screen,but there is none...only dark screen...when screen is connected and i press F8 to turn the image over to the external monitor, the external monitor gets coloured bars ,but when i disconnect the cable from the EDP ,the HDMI picture is good...What could be the problem? I don't have another edp cable, but i measured it with meter and it comes out good...i am baffled... i have the schematics and tried measuring signals, and DV1 and DV2 are no voltage...+BL_PWR_SRC is present, +5V_TSC also present...EDP signals go directly to PCH...

[mcplslg123]

Check +LCDVDD is present or not? The voltage should be 3.3V here. If this voltage goes below 3V, your internal screen wont work at all(Even backlit wont work).

[huzo]

i have attached the edp connector pinout...there is no +LCDVDD there mentioned---There is +BL_PWR_SRC , +5V_TSC also present

[mcplslg123]

i have attached the edp connector pinout...there is no +LCDVDD there mentioned---There is +BL_PWR_SRC , +5V_TSC also present

Just use search option on your pdf reader and type +LCDVDD. I can see it even in the screenshot shared by you.

[huzo]

It is NOT called +LCDVDD, it's not my first time using the schematics ...and for some reason i can't search inside pdf and i can't copy any text...For example there is a word, and when i copy it i get random signs..for example it says +3.3V_RUN_UT9(some random text) and when i copy it i get /!01212 # ...i don't know if it's some kind of a security feature or what...But if you look at the image at first post .there is no +LCDVDD pin...

[mcplslg123]

On screenshot CV12 is the place where you can measure LCD_VDD and its shown just below the edp1 connector.

This voltage may have changed the name when it goes to EDP connector but lcd vdd is always there on edp connector.

Friend i dont have the habit of undermining someone else's knowledge/skills-so where did i say u dont understand schematics?

If you so wish, i wont comment.. Sorry if i hurt you.

[piernov]

It IS called +LCDVDD. Pin 30/31. It's not mcplslg123's first time using schematics either, and fixing laptops…

PDF file text is broken, happens when idiots insert their obnoxious watermark on all pages… gotta do with what we have.

[huzo]

On screenshot CV12 is the place where you can measure LCD_VDD and its shown just below the edp1 connector.

This voltage may have changed the name when it goes to EDP connector but lcd vdd is always there on edp connector.

Friend i dont have the habit of undermining someone else's knowledge/skills-so where did i say u dont understand schematics?

If you so wish, i wont comment.. Sorry if i hurt you.

I apologise ,i was nervous that day and tired and didn't see properly,you are ofcourse right and once again i do apologise to you, i know you are senior members and professionals...I honestly didn't see pins 30/31 because there is something writen over them...I thought they renamed the +LCDVDD to something else and the language barrier got us to misunderstanding...

piernov as i mentioed above, i apologise for my behaviour, i know both of you from the forum and i know you are pros...but i somethimes loose my mind and say stupid things Ok, i will check that...


The +LCDVDD is present on pins30,31, 3,37V, and pin 26 EDP_HPD is 2.4V, that's normal for EDP_HPD?

[FriedFred]

So do you think, the voltages are correct? Then there might be a problem with the data lines. You see, there are some little capacitors in series in the data lines. Please check them, whether you have traffic on them.
There is also usually a LVDS-switch IC, which switches the LVDS-signals between the inner display and the outer HDMI port. Once I have had a burned LVDS-switch. Took me some time to find it.

[huzo]

Yeah i've measured them,they are not shorted...i don't have an osciloscope to measure signals...i am going to look further....

[FriedFred]

You don't need a scope to detect data traffic on a data line. Just measure the voltage. If you have something like 0,5V or higher, then there might be a data traffic on the line.
Please note, if you measure a data line, which has a small capacitor in series, you need to measure with "AC". Because DC voltage is blocked by this series-capacitor.

"but when i disconnect the cable from the EDP ,the HDMI picture is good...What could be the problem?"
This can be likely that a data line is shorted on the display board.
Do the voltages also get some change if you connect/disconnect the eDP cable?

[huzo]

i tried,cant see any voltage...

i've tried two other screens,all the same...

I've checked,the signnals are going directly to the PCH,EDP is different from LVDS,has no switching chip...so probably something in PCH is bad...HDMI data lines also go directly to PCH...So probably PCH?

[FriedFred]

Indeed, this sounds a bit like the PCH is in trouble.
But it can also be, that the switching between those LVDS-lines does not work and the PCH is still okay.

"when screen is connected and i press F8 to turn the image over to the external monitor, the external monitor gets coloured bars ,but when i disconnect the cable from the EDP ,the HDMI picture is good"

Can you choose to get a picture from internal and external display synchronously? Both displays at the same time?

[FriedFred]

I think, a little capacitor in series with a data-line is the problem. Please check carefully the connections from the CPU over the capacitors to the eDP-Port and the HDMI-Port. If we still assume the PCH is okay, there might be the problem. Maybe a capacitor is missing or so.

[huzo]

There are caps, but they don't test short...the lines go directly from PCH, it's different from LVDS system...The hdmi and edp lines go from different PCH pins...

The board is thrown to the scrap for parts, i've got another board from broken laptop and with bad battery...