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Old 05-25-2018, 04:35 AM   #1
Pierre95
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Default Compaq pressario CQ61 display issue

Hello,

I have a display issue which looks like shown on the attached pictures:

Description: after power-up backlight illuminates itself, the display is black as if everything gets fine. However no bios message is displayed. The display remains black for a few seconds, then starts slowly to get brighter so that the initial perfectly black picture slowly fades out to become some gray color (first attached picture). Some pixels appear green like if they were hot pixels. After lets say 2 minutes the display stabilizes itself as on the second picture (the left edge is blue).

It seems that something is wrong with the LVDS signals. The display works perfectly when attached to another computer.

I first thought it was an LVDS controller issue. However, once the display initialized correctly and worked fine for let's say 30 minutes. So I powered the PC OFF and ON, to see if this was not some bad contacts issue, but I got this issue again...

Can it be related to a slowly dying LVDS chip which sometimes works again?

How can I test the LVDS signals? It requires some fast scope, right?

Thanks a lot for your help
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File Type: jpg 20180525_010814.jpg (111.8 KB, 24 views)
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Old 05-25-2018, 04:47 AM   #2
mielta
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Default Re: Compaq pressario CQ61 display issue

Hi
When the LCD is Fine i think it is an lvdskabel issue
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Old 05-25-2018, 07:30 AM   #3
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Default Re: Compaq pressario CQ61 display issue

It would have made sense but I forgot to point out, I just replaced the lvds cable by a new one as the backlight power supply wire was cut off somewhere in the middle of the cable. When I first turned on the PC after cable replacement, everything worked correctly, then I switched OFF the PC and on tomorrow I got this issue.
So I tried the display unit on another PC which prooved the LCD was OK, then attached the lcdback to the CQ61. After power up the display worked again but when turning OFF and ON again, the problem was there... And now it is visible everytime.
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Old 05-25-2018, 08:37 AM   #4
mielta
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Default Re: Compaq pressario CQ61 display issue

i think thats Grafikchip
if you have an hotairstation you can it heating alittlebit and then see the result.
when it is ok you must change the GPU but you must have an BGA-Station.
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Old 05-25-2018, 10:38 AM   #5
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Default Re: Compaq pressario CQ61 display issue

If you have ATI graphics, yes, it is graphics chip problem.
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Old 05-28-2018, 07:50 AM   #6
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Default Re: Compaq pressario CQ61 display issue

I'll check if this is ATI or NVIDIA.

mielta you mean heating the graphic chip may bring it temporary in working conditions?

I will also check my PSU to be sure it feeds enough power.
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Old 05-28-2018, 08:00 AM   #7
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Default Re: Compaq pressario CQ61 display issue

lcd cable issue
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Old 05-28-2018, 09:11 AM   #8
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Default Re: Compaq pressario CQ61 display issue

Quote:
Originally Posted by Pierre95 View Post
mielta you mean heating the graphic chip may bring it temporary in working conditions
In most cases it does.
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Old 05-29-2018, 07:28 AM   #9
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Default Re: Compaq pressario CQ61 display issue

So if I understand well, heating the chip will temporary reestablish bad contacts through a thermal expansion phenomena? Or it will change electrical properties of the chip so that they fall in working conditions for the duration of heating?
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Old 06-07-2018, 09:48 AM   #10
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Default Re: Compaq pressario CQ61 display issue

I tried connecting another display with slighltly smaller dimensions and, surprisingly it works. The image is not displayed on the whole area most likely because of the smaller size and maybe different aspect ratio but this prooves the LVDS signals are still there. This therefore invalidates the faulty graphic chip option.

So:

CQ61 display on another computer: working
Other display on CQ61: working
Original display on CQ61; not working.

I already checked display's power voltage which is 3,34V. I'll check its raising time with the help of an oscilloscope as a slow raising time could mean the display is badly initialized.
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Old 07-29-2018, 06:56 AM   #11
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Default Re: Compaq pressario CQ61 display issue

I made recordings of the EDIDCLK and EDIDDATA signals at power up with:
1/ the original display which does not initialize properly. The communication lasts for about 300 microseconds then stop.

2/ another display which initializes properly. The communication lasts for about 11ms.

I am a bit confused in understanding the exchanged data. The first byte is the address 50h then the displau outputs the first byte of the EDID header?
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File Type: jpg SDAecranOK.JPG (80.8 KB, 4 views)
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Old 10-16-2018, 08:06 AM   #12
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Default Re: Compaq pressario CQ61 display issue

I finally succeeded in solving this issue which was due to broken soldering joint at the EDID VCC (3V) LVDS connector pin on the motherboard.

Some displays seem to not care about if EDID data is returned or not, but the original display simply doesn't initialize when no EDID data is received.

Last edited by Pierre95; 10-16-2018 at 08:12 AM..
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Old 10-16-2018, 08:27 AM   #13
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Default Re: Compaq pressario CQ61 display issue

Thank you for the report, I have seen this before and a replacement screen fixed it, i was wrong about the graphics chip being the cause of this issue on this particular model. It's great that you got the original screen working.
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Old 04-28-2019, 04:34 AM   #14
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Default Re: Compaq pressario CQ61 display issue

You're welcome. Yes it's great being able to keep the original display as it is not used too much.
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