Hi Sir:
Please do the follow steps:
1) Perform a visual inspection : look for loose and broken wires, improperly seated connectors, loose or
broken wires
misset switch, missing jumpers. and so on.
Chech for obviously damaged component(components burned or discolore due to overheating);
Dust + dirt + tear +wear
2) Reseating Boards and components:
Edge connectors are a common source of problems. Power down the system and remove the PC
boards. Examine the edge connectors
for contamination and clean with pencil eraser+ contacts cleaner contacts. Reseat any loose components such as
socket the ICs) . Reseat the boards and power up.
3) Power supply checks:
Check the power supply for missing voltages and voltages out of spec. A digital multimieter DMM can
be necessary, as
voltage specifications are quite tight: logic supplies for example: must be within + 0.7% percent of
5Vdc up or down . All the
multiple supplies and all must be checked.