Tektronix WFM5250, Service Manual

Page: 35 / 57

Troubleshooting
Basic Power Supply
Checks
This section describes methods for verifying the proper operation of the
basic power supplies on the Video I/O board. This procedure requires partial
disassembly, and should only be performed if the unit fails to produce evidence
of CPU boot up.
WARNING.
Internal power supplies are all low voltage so no safety shield is
present.
This instrument requires an external DC power source capable of providing 11
to 17 V
DC
at 3A. The provided AC adapter accepts 90 to 264 V
AC
and outputs
around 12 V
DC
with 4 A capability. This voltage passes through a power switch
circuit on the Video I/O board, and is present at the "+12V" test point if instrument
power is on.
The sw12V 5V and +3.3V switching power supplies, also
located on the Video I/O board. These three voltages are the basic power supplies
distributed to the rest of the instrument.
Remove the Reference I/O and FPGA boards to gain access to the Video I/O
board power test points. Locate the +12V, +5V and +3.3V test points on the
Video I/O board. (See Figure 2.) Measure the voltages with a DVM and check
against the allowable ranges. (See Table 5.) If the voltages are outside of the
allowed range, replace the Video I/O board. If voltages are within the allowed
range, replace the CPU board.
Table 5: Video I/O board basic supplies
Nominal (+V) Allowed range (+V)
+12V 11 to 17
+5V 4.85 to 5.15
+3.3V 3.2 to 3.4
WFM5250 Waveform Monitor Service Manual 19