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IBM 5151  -  Power-Up


Unlike the 5151's successors, the 5153 (CGA) and 5154 (EGA), you will not see any display at all (not even a raster) if the 5151 is not connected to an operating MDA video card.  This is because of the design of the 5151.  For the high voltage (14 KV) to be generated, there needs to be a horizontal sync signal coming into the 5151.


If the 5151 has power alone, i.e. not connected to an operating MDA video card, operation of the 5151's components are as follows:

Component	Operates	Comment
+15V DC out of power supply	Yes
+5V DC out of power supply	Yes
+55V DC	No	For this, the 5151 requires an incoming horizontal sync signal.
-170V DC	No	For this, the 5151 requires an incoming horizontal sync signal.
+450V DC	No	For this, the 5151 requires an incoming horizontal sync signal.
Vertical deflection circuitry	Yes	Free-runs (at less than 50 Hz) if no incoming vertical sync signal.
Horizonal deflection circuitry	No	For this, the 5151 requires an incoming horizontal sync signal.
CRT filament  (cathode heater)	Yes	Uses +15V DC out of power supply.  Diagram here.
14 KV generation for CRT	No	For this, the 5151 requires an incoming horizontal sync signal.

		WARNING: Opening the 5151 will expose you to dangerous voltages and currents. Those threats can still be present long after power has been disconnected from the 5151. Before opening the 5151, adequately educate yourself as to the hazards. Some hazard examples at here.