Display Board; Table 4-2 Power Supply Components - Keithley 2701 Service Manual

4-6 Troubleshooting
AC power is applied to the AC power module receptacle. Power is routed through the line
fuse and line voltage selection switch of the power module to the power transformer. The
power transformer has a total of four secondary windings for the various supplies.
AC voltage for the display filaments is taken from a power transformer secondary at F1 and
F2, then routed to the display board.
Each DC supply uses a rectifier and a capacitive filter, and many supplies use an IC regula-
tor. Table 4-2
Table 4-2
Power supply components
Supply
+5VD
+3.3VD
+2.5VD
+1.8VD
+37V
+15V
-15V
+5V, +5VRL, +5V2
+18V
-18V

Display board

Display board components are shown in the digital circuitry block diagram in
Microcontroller
U401 is the display board microcontroller that controls the display and interprets key data.
The microcontroller uses three internal peripheral I/O ports for the various control and read
functions.
Display data is serially transmitted to the microcontroller from the digital section via the
TXB line to the microcontroller RDI terminal. In a similar manner, key data is serially sent
back to the digital section through the RXB line via TDO. The 4MHz clock for the
microcontroller is generated by crystal Y401.
summarizes rectifier, filter, and regulator circuits for the various DC supplies.
Rectifier
CR104
-
-
-
CR115, CR117
CR102
CR102
CR103
CR102
CR102
Model 2701 Service Manual
Filter
C156, C273, C274, C281
C66
C205
C214
C104
C148
C131
C146
C148
C131
Regulator
U144
U18
U25
U19
U101
U125
U119
U124
-
-
Figure 4-2.