Touchscreen test - find dead zones and check multi-touch

Two faults, two ways of finding them

A touchscreen fails in two distinct ways, and they need different tests.

Dead zones are areas where the digitiser has stopped registering contact - usually after a drop or a screen replacement. You find them by drawing: a line dragged across a dead zone comes out with a gap in it, and a gap is obvious to the eye in a way that no number is.

Multi-touch failure is a drop in how many fingers the screen tracks at once. Panels advertise ten points and sometimes deliver fewer; a damaged digitiser often falls to one or two, which breaks pinch-to-zoom and typing.

How to test properly

1. For dead zones: drag one finger slowly in overlapping passes until you have covered the whole area, edge to edge. Go slowly - a fast drag naturally leaves a sparser line and can look like a fault. Then look at the picture as a whole.
2. Test the edges especially. Edge damage is the most common kind, and it is the area people cover least.
3. For multi-touch: press five fingers down together and check the "most at once" figure. Repeat with all ten if your screen claims ten.
4. Press Clear and repeat if you want a fresh surface.

Reading the result

• A clean, continuous drawing - the digitiser is reading the whole panel.
• A repeatable gap in the same place - a dead zone. Repeatable is the important word; one sparse patch from a fast drag is not a fault.
• Lines that jump or jitter - often a cracked digitiser, a bad screen protector, or a cheap charger. Unplug the charger and try again; poorly filtered power supplies are a genuinely common cause of phantom touch input.
• A low multi-touch peak - try again making sure your fingers land far apart. Two fingers very close together are sometimes merged into one contact by design.

Before you conclude the screen is broken

Take the case and screen protector off and retest. A protector with trapped dirt underneath, or one that does not sit flat, produces exactly the symptoms above. Clean the screen with a dry cloth - moisture and grease both interfere with a capacitive digitiser. And if the phone has been in the cold, let it reach room temperature first.

What the readings mean

Input type shows whether the browser sees a finger, a stylus or a mouse. Pressure appears if your hardware reports it - most phones do not, and a stylus usually does; a device that reports no pressure is not faulty.

Privacy

Everything is drawn and measured on your device. Nothing you draw is uploaded, and nothing is kept after you close the page.