COF stands for Chip-On-Film — the thin, flexible strips bonded along the top or side edge of an LED TV panel. Each COF carries a driver chip that controls a vertical slice of the screen. If one COF loses contact or its chip fails, you get vertical lines or a wide vertical band in that section of the picture.
COF repair is specialised work. The strip is bonded to the glass using ACF (anisotropic conductive film) with micron-level alignment. City Electronics has a dedicated panel bonding machine that lets us remove a faulty COF and bond a new one, with controlled temperature, pressure and time. Few repair shops in the Aligarh area offer this.
Panel ki COF patti kharab ho to poora screen badalne ki zarurat nahi — bonding machine se COF badal dete hain.
Common symptoms
- A wide vertical band of wrong colour
- Group of vertical lines in one section of the screen
- A vertical section completely black or white
- Lines that move or change when the top edge is pressed
- Vertical lines that appear after the TV warms up
What causes it?
Bond weakening over time
Heating and cooling every day slowly weakens the ACF bond, breaking contact.
Driver IC failure
The chip on the COF itself fails — the COF then needs replacement, not just re-bonding.
Physical stress
Bending the panel during transport or wall-mounting cracks fine COF traces.
Moisture
Humidity can corrode the COF contacts over time.
How we fix it
- 1We confirm with test patterns which COF position is faulty.
- 2The panel is opened and the COF area is cleaned and inspected under magnification.
- 3The faulty COF is removed and residue is cleaned from the glass.
- 4New ACF is laid and the replacement COF is aligned and bonded on the machine.
- 5Contact is verified with patterns, then the TV runs a long burn-in test.
Typical turnaround
1 to 3 days
COF repairs typically take 1 to 3 days, depending on whether a replacement COF is in stock for your panel type.
Frequently asked questions
Is COF repair the same as panel repair?
COF repair is one type of panel repair. Panel repair is a wider term that also covers gate-side faults and other display issues.
Can COF repair fix a cracked screen?
No. If the glass is cracked, the panel needs to be replaced. COF repair is for lines and bands where the glass is intact.
Do you use a machine or do it by hand?
We use a dedicated panel bonding machine. Hand-soldering or heat-gun methods are unreliable on COFs and often fail quickly.