Black screen after reattaching COF, purple bars without it.

[unimatrix93]

Hello there.

I have a Phillips with de attached COF cable (the glue let it go) that had lines on its display.

After I found out that the COF cable is dangling from the LCD panel, I looked up online if I can fix it without a bonding machine.

After tinning the COF cable and the PCB contacts I proceded to solder them together.

It was very tedious but using my tweezers, my phone as microscope and a shitton of agility I managed to bond them with my soldering station.

Now, with the COF cable reattached the lines are gone, but the screen is black, only the backlight is working and if I remove the COF cable with my hot air station the display shows purple and white, vertical bars with a black bar in the middle(where the COF is deattached).

I can upload pictures and even videos of the tinning of the contacts and of the reattached COF too if you wish.

What should I do now, guys?

[nomoresonys]

Re: Black screen after reattaching COF, purple bars without it.

sure upload the pics. and video, maybe someone can figure it out.

[unimatrix93]

Re: Black screen after reattaching COF, purple bars without it.

Here is two close up footage of the COF and the PCB after tinning.

COF tinning
PCB tinning

Close up photos of the end result:

[unimatrix93]

Re: Black screen after reattaching COF, purple bars without it.

I measrued the TCON board voltages, here are the results. V18 has 0.5v which is suspicious.

VGH_ODD: 28v between -7v
VGH_EVEN: Same
VST: - 7v
VCOM: 5.7v
VCOMRFB: 5.7v
V1: 16v
V9: 8.4v
V14: 3.9v
V5: 12.2v
V10: 7.8v
V18: 0.4v
VCC: 3.3v
HVDD: 8.1v
VCORE: 1.2v
VDD: 16.7v
VCC18: 0.2v

[Unspun01]

Re: Black screen after reattaching COF, purple bars without it.

Here is two close up footage of the COF and the PCB after tinning.

Hi unimatrix93:

I have performed this exact repair as you when I had a COF ribbon cable become detached from buffer board (also on a philips LCD panel, but due to an accident by a slight tug on the board)

You may have some pins making connection, and some pins not making connection, or accidental solder bridging between adjacent pins.

My advice it to detach the flex cable, and try re-soldering.

USE LOTS OF FLUX, FRESH SOLDER, and VERY FINE SOLDER TIP.

Use scissors to trim the entire top edge of the flex cable (like 1mm or 1/16" or whatever is the least amount) to expose the very edges of the solderable pads on the flex cable.

Don't use too much solder, but ensure each pad on the flex ribbon is tinned, and each pad on the buffer board is tinned. Then flux everything. Then using the fine point solder tip, align the left or right most pad to ensure correct alignment. Then use individual pin soldering in consistent left-to-right, or right-to-left order. Or use DRAG-SOLDERING. If you have lots of flux, and the appropriate amount of solder, these connections will each be re-made properly without solder bridges.

You also need to ensure the ribbon cable and buffer board are perfectly 90degrees to each other. Even slight mis-alignment between such fine pitch pins can cause adjacent pins to become connected at the end of worst mis-alignment.

EXAMINE your work with MAGNIFYING LENS. I cannot stress enough that you need to be sure extra solder is not shoring anything out.

In my case I had 100% success, but not before identifying a couple of spots where I noticed excess solder trapped between the board and the flex ribbon that could have caused an issue. I tested and re-tested because I was working on a 75" TV, and absolutely needed to be sure my work was perfect and not going to short out the panel.

Best of luck.

[unimatrix93]

Re: Black screen after reattaching COF, purple bars without it.

Hi unimatrix93:

I have performed this exact repair as you when I had a COF ribbon cable become detached from buffer board (also on a philips LCD panel, but due to an accident by a slight tug on the board)

You may have some pins making connection, and some pins not making connection, or accidental solder bridging between adjacent pins.

My advice it to detach the flex cable, and try re-soldering.

USE LOTS OF FLUX, FRESH SOLDER, and VERY FINE SOLDER TIP.

Use scissors to trim the entire top edge of the flex cable (like 1mm or 1/16" or whatever is the least amount) to expose the very edges of the solderable pads on the flex cable.

Don't use too much solder, but ensure each pad on the flex ribbon is tinned, and each pad on the buffer board is tinned. Then flux everything. Then using the fine point solder tip, align the left or right most pad to ensure correct alignment. Then use individual pin soldering in consistent left-to-right, or right-to-left order. Or use DRAG-SOLDERING. If you have lots of flux, and the appropriate amount of solder, these connections will each be re-made properly without solder bridges.

You also need to ensure the ribbon cable and buffer board are perfectly 90degrees to each other. Even slight mis-alignment between such fine pitch pins can cause adjacent pins to become connected at the end of worst mis-alignment.

EXAMINE your work with MAGNIFYING LENS. I cannot stress enough that you need to be sure extra solder is not shoring anything out.

In my case I had 100% success, but not before identifying a couple of spots where I noticed excess solder trapped between the board and the flex ribbon that could have caused an issue. I tested and re-tested because I was working on a 75" TV, and absolutely needed to be sure my work was perfect and not going to short out the panel.

Best of luck.

Thank you so much for the detailed reply! I will try again next week and with my shiny new microscope, which will help me check on the soldering.