Troubleshooting Video/Display Problem

Whenever there is a display problem, the first step is to find out what could be the cause of the problem, is it due to incompatible display card and monitor or is it incorrect configuration information or is it due to faulty monitor or faulty display adapter card.

The display card and monitor are quite reliable but a gradual apperance of faults with age is very common. Many display related problems are caused by incorrect configuration and cable fault. Another common reason of blank display could be monitor's power switch being OFF or the brightness being turned down.

There are many thing that can cause display problems. Some of the most common faults are listed below. 

Monitor Dead

• Monitor's fuse blown.
• Monitor's power supply section faulty.
• Fault in horizontal section.

On Power-On system beeps but no display appears

• Setup information incorrect.
• Display adapter not seated properly in expansion slot.

Power on LED glows but no raster

• Power Supply voltage abnormal.
• Some loose connection in power supply circuit.
• Brightness control is in extreme OFF position.

Abnormal brightness in display

• Power supply voltage output high.
• Screen voltage (G2) high.

  Bright spot on screen

• Note: decrese brightness to minimum

Warning: This may damage the CRT permanently.

• Monitor cable broken or loose-connected.
• Faulty monitor deflection circuits (Vertical and Horizontal).
• Display adapter fault, try another adapter.
• CRT defective.

After switching on the system, raster appears after sometime and defocused display

• CRT weakening or CRT aging.

Display intermittent

• Loose contact in video circuit.
• Display cable loose.
• Loose contact in CRT base.

Small or stamp type raster

• Power supply voltage output low.
• No regulation in power supply.
• Fault in bridge rectifier circuit.
• Main filter capacitor in power supply dry.

Only one horizontal line appears

Note: decrease brightness to minimum

Warning: This may damage the CRT permanently.

• Deflection yoke's vertical winding is loose or open.
• Loose contact in vertical section or print open.
• vertical circuit fault.

Only one vertical line appears

Note:decrease brightness to minimum

This may damage the CRT permanently.

• Deflection yoke's horizontal winding is loose or open.
• Circuit fault between EHT and horizontal winding.

Improper height or the display

• Check circuit of vertical output section.
• Supply to vertical section low.
• Supply resistance of vertical section has increased.
• Fault in feedback circuit (output to input).
• vertical height preset misadjusted.

Vertical non-linearity in character size from top to bottom in a coloumn

• Fault in feedback circuit (output to input).
• Vertical linearity preset misadjusted.
• Coupling capacitor dry.

Horizontal non-linearity in character size from left to right in a row

• Linearity coil-if provided-misadjusted.
• Capactor value between EHT and horizontal winding not proper.

Display shaking

• Open diode in power supply - bridge rectifier circuit.
• Main filter capacitor dry.
• Power supply regulation not proper.
• Electromagnetic interference.

Unsteady display, moving band on screen

• Inteference in supply line.
• Power supply voltage very low.
• Power supply circuit faulty.

Display out of sync

• Cable not connected properly.
• Vertical/horizontal hold misadjusted.
• Monitor synchronization circuits needs adjustment.
• Display mode not supported by monitor.
• Wrong software driver for display adapter.

Display rolling in horizontal direction

• Horizontal hold control misadjusted.
• Cable loose contact.

Display rolling in vertical direction

• Vertical hold not adjusted properly.
• Cable loose contact.

Fold-over in the begining or end of scan line

• Phase control preset misadjusted.
• Fault in vertical output or horizontal output section (component value deviated).

Brightness control not working, abnormal or no change in brightness

• Brightness control defective.
• Abnormal grid voltage (G2)

Spot sceen when switching off

• CRT weakening.
• CRT aging.

Black vertical bar on the screen

• Control grid (G1) voltage not proper.
• Control grid (G1) circuit defective.

Defocusing of dots

• Improper focus voltage.
• CRT deterioration.

Weak contrast

• Failt in video circuit.
• Fault in contrase control circuit.

Raster ok, no video

• Video cable contact not proper.
• Fault in video circuit.

Noisy display

• Problem in grounding.
• Video cable loose contact.

Fine noise on the screen (white spot)

• Contact problem in connectors.
• Leakage in high voltage protection.

Corrupt display

• Software corrupts dislpay adapter memory.
• Display adapter memory (RAM) faulty.

Distorted characters on screen

• Display adapter fault.

No cursor

• Software fault.
• Adapter not fully IBM-compatible.

"CMOS Display Type Mismatch" Error On power on

• CMOS setup incorrect for type of display, run SETUP.

Corners of the display are improper

• Adjust ring magnets located on deflection yoke.

Display on the screen is displaced to one side

• Centering magnets of deflection yoke misadjusted.

Display title towards one direction

• Deflection yoke tilted due to loose fitting.

Virus Infection Symptoms

Some of the very common shown by a system infected by a virus are given next.

Unexpected slowdown of the System

This is one main symptom of the virus infection. If the system without any apparent reason starts to take more time to load programs from the disk or starts to operate slower than its normal speed then you can suspect a virus infection.

Decrease in the amount of available memory

This is another symptom of virus infection. When checked with the CHKDSK, the system shows some KB of memory missing from the main memory or when checked with the MEM/D/P command, the memory module list shows some program resident in the memory without any proper module name.

Increase in BAD Sectors/Lost clusters etc.

When the number of bad sector start increasing, or when the number of lost clusters reported by the SCANDISK or CHKDSK start increasing without any special reason then one main reason behind this could be a virus infection

Cannot Execute Executable Files

If you find that the executable files (.EXE, COM etc) which you are able to execute till yesterday start missing from the directories or when executing them you start getting some errors messages then this again could be one major indication of the virus attack.

Screen Shows Some Unusual Outputs

Getting of some message such as “legalize marijuana” or dropping of letter to the bottom of the screen or some special character appearing or moving of virus infection.

Another indication could be some music being played by the computer without running any special music program.

Drive’s Light Turns on

The drive’s light may turn on indicating that a read or write is taken place even when you have not given any read or write to the disk without any write command being issued are some other symptoms of virus infection.

Some software as windows keep temporary data on the disk read and writes to them periodically.

New “.COM” files appear for the “.EXE” files

This shows a companion type virus where the virus stays as a .COM file for and .EXE file. This gives the virus a chance to get executed because the DOS always executes the .COM file before executing a .EXE file of both the files are of same name.

Some DOS program and utility program contain both .COM and .EXE file with the same name. For example, the DOS program MSD (Microsoft Diagnostic) contains both MSD.COM and MSD.EXE.