Vertical line on a DMG screen: reflowing the LCD ribbon

Confirming it is the ribbon and not the driver

A line that flickers or changes when you press the front of the screen is a ribbon bond fault. A line that is rock steady and identical on every boot could still be the ribbon, but it could also be a failed column driver output on the LCD itself, which is not repairable.

Test with the console running a game that fills the screen with a solid pattern. Count the lines and note exactly which columns they are. Photograph it. You need to know after the repair whether you fixed the right ones, and the screen looks very different once the shell is open.

Deciding whether to attempt the reflow

Look at the ribbon where it meets the glass under a magnifier. The bond should be a uniform grey-brown band. A bond that has failed shows a lighter or darker patch at the line position, sometimes with a visible gap or a bubble.

Check for the other classic cause first: corrosion on the ribbon where it folds around the LCD frame. Liquid that got into the shell collects at that fold and eats the traces. A ribbon with visible green or black corrosion at the fold is usually beyond saving, and the honest answer is a replacement screen.

1. Open the shell and remove the main board so the LCD and its ribbon are cleanly accessible.
2. Inspect the ribbon-to-glass bond under 10x magnification with side lighting. Note any light or dark patch.
3. Inspect the fold of the ribbon for corrosion. Flex the ribbon gently at the fold while the console is running and watch for lines appearing or disappearing.
4. Press the ribbon against the glass with a soft eraser while the console runs. If the line disappears under pressure, the bond has failed mechanically and a reflow has a good chance.
5. If pressing has no effect at all and the ribbon is clean, the LCD column driver has failed. Stop and tell the owner a replacement screen is needed.

Reflowing with heat and pressure

This is the hardest routine job in Game Boy repair. The ribbon is bonded with a heat-activated anisotropic adhesive that reflows around 180 to 200 °C. Too little heat and nothing happens; too much and the ribbon delaminates or the polariser behind the glass is damaged. Use a temperature-controlled iron with a wide flat tip wrapped in silicone sheet, or a proper thermode tip if you have one.

Work in short strokes, one line at a time, with firm even pressure. Go over the same area three or four times rather than holding heat on one spot. Let the area cool between passes. Check the screen after every two passes; the lines usually come back one at a time rather than all at once.

1. Set the iron to 190 °C. Wrap the tip in a small piece of silicone sheet or PTFE tape so it cannot scratch the ribbon.
2. Support the LCD from behind with a soft pad so the pressure goes into the bond and not into the glass.
3. Press and drag slowly along the bond line where the fault is, about two seconds per centimetre.
4. Power up and re-check. Repeat up to four passes. Stop if the line does not change after four.
5. If the line changes but does not go away, the bond is partially restored. Continue with shorter, cooler passes rather than turning the heat up.
6. Reassemble and let the console run for thirty minutes. A bond that is going to separate again usually does so once the LCD is warm.