Voltage Checks - HP 98780 CE Handbook

98780 Troubleshooting
4-3
Voltage Checks
The mainframe power supply voltages can be checked in the 98780A. Figure 4-1 shows the test
points and the corresponding voltages.
+5
-18
-60
GND
+800 V
-12
+12
+5R
-18 +18 +5
V
Figure 4-1. Voltage Test Points
Table 4-1 shows the distribution of the various voltages in the 98780A.
Table 4-1. Voltage Distribution
Voltage Comes from Used
+ 18 volts Mainframe 98780-66513 Heatsink, A12/A14 Deflection
Power Supply A21 Display Logic. 98775-66504 light Pen,
All CRT Drive
-18 volts
Mainframe 98780-66513 Heatsink, All CRT Drive
Power Supply A12/A14 Deflection, A21 Display Logic
98775-66504 light Pen
+
12 volts
Mainframe
A31 I/O, All CRT Drive, A12/A14 Deflection,
Power Supply
A511A52 Graphics
-12 volts Mainframe
A31 I/O, A12 Deflection, A51/A52 Graphics
Power Supply
+5 volts Mainframe
All PC assemblies except 98780-66513 Heatsink
Power Supply
+5R
Regulator A12/A14 Deflection
on A12/A14
+ -15 volts
Regulator A12/A14 Deflection
on A121A14
I