9517 / 8517 Monitor Function Checks

USE ONLY THIS REFERENCE TO SERVICE YOUR IBM MONITOR!

SHSA380053.BOO PS/2 Display Hardware Maintenance Manual,Vol 1

 

2.5.2.1 Function Checks  [Test Raster]

 

Location of RV508 and D2 


 

Symptom

Action

Any problems

First, check all connections and plugs for continuity

Green LED lit but test raster missing

Adjust RV508 (G2) clockwise until a background raster appears

- If no raster appears, replace analog card

- If raster still absent, replace ITC

- If background raster appears, replace video card

Test raster is not white

Adjust video levels and cutoffs for correct colorpoint 

- If no improvement, replace video card

Test raster is multicolored

Ensure that D2 is connected.

Turn power off 30 minutes, and then on to check degauss action

Check continuity of degauss coil

- If defective, replace ITC shield, otherwise replace analog card

Test raster scan collapsed,

Horizontally or Vertically

If partially collapsed, adjust as appropriate

If fully collapsed, replace analog card

1.2.4 Degaussing

  The effect of stray magnetic fields on the color purity of an Integrated Tube Component (ITC) depends on the orientation of these fields with respect to the ITC. Color displays have a magnetic shielding system, consisting of a magnetic screen (internal to the ITC), and the shadow mask (together with its mounting frame), to combat stray magnetic fields.

  To be effective, the shielding system must be degaussed by applying a strong alternating magnetic field which decays gradually and symmetrically to zero.

  This is achieved by using dual, positive temperature coefficient resistors (PTC) in conjunction with a degauss coil on the ITC. When the mains input voltage is applied to the display, the peak inrush current through the coil is limited by one half of the dual PTC, while the other half is heated by the current flow in it. Equilibrium is achieved when the heat in one half of the PTC is sufficient to prevent current flow in the other half, and consequently in the degauss coil.

  When degaussing is required, (for example, if a display is relocated) the heating associated with a degauss action means that another degauss action cannot be started until the circuit has cooled down.

  Allow at least 30 minutes with the display powered off, before starting another degauss action.