5-10
Voltage source
The various voltage source circuits include the digital inter-
face, the DAC, range control, and the power output stage.
Each of these sections is briefly discussed below.
Serial voltage source control information is converted into
parallel form by U303-U306. U304 is a latch that stores
range and operate information, while U305 and U306 store
the 16-bit data word for the voltage source output value.
The 16-bit data word that represents the voltage source value
is converted into analog form by U308, a 16-bit DAC. The
voltage reference for U308 is generated by regulator U309.
The voltage source itself is actually a compound operational
amplifier. U307 provides the overall stage gain, while power
output capabilities are supplied by Q311-Q317. Note that the
±120V supply is used to power the output stage on the 100V
range, while the ±1200V supply powers the output stage on
the 1000V range.
Voltage source ranging is provided by selecting feedback
resistor values with elements of U312. Approximate voltage
gain on the 100V range is
×
20.5, while the 1000V range gain
is
×
207.9.
5.6
Circuit board checks
Basic troubleshooting checks for the various circuit boards
are covered below.
5.6.1 Display board checks
If the FRONT PANEL TESTS (paragraph 5.4) indicate that
there is a problem on the display board, use Table 5-2. Cir-
cuit theory for the display is provided in paragraph 5.5.1.
Drawing reference: Display Board; 2002-110
Table 5-2
Display board checks
Step Item/component
Required condition
Remarks
1
2
3
4
5
6
7
FRONT PANEL TESTS
P1033, pin 5
CR902 cathode
P1033, pin 12
U902, pin 43
P1033, pin 10
P1033, pin 8
Verify that all pixels operate
+5V, ±5%
+60V, ±10%
Goes low briefly on power-up, then goes high
4MHz square wave
Pulse train every 1msec
Brief pulse train when front panel key pressed.
Use SELF-TEST MENU selection
D5V supply
VFD +60V supply
Microcontroller RESET line
Controller 4MHz clock
Control from main processor
Key down data sent to main processor.