Fluke 2680A Service Manual page 181

Table 6-10. Hints for Troubleshooting "Dead" Devices
Possible Fault
Blown Fuse
Power Supply
Dead A2 Display PCA
Dead SYS/CTRL Microprocessor
Power-On Reset
Diagnostic Testing and Troubleshooting
Discussion
If the device is completely dead, you may have blown the
line fuse. There is also a fuse inline with the DC voltage
input for battery input protection. Either power input can
operate without the other working. See Chapter 3 for fuse
replacement instructions.
Self-test starts with the outguard Sys/Ctrl PCA. If self-test
won't even begin, then something is wrong either at the
Sys/Ctrl PCA or with a power supply voltage. If the A/D
Power module PCA has a short circuit of some kind, it
could load down a power supply voltage such that the
current limiting feature is folding the supply back. For
example, the +5.6 V dc Vdd supply might only measure
1.2 V dc. This in turn would kill the Sys/Ctrl PCA. To check
this possibility, turn the device power off; then pull out all of
the modules. Power the device again. If this time the
device goes into self test, then you need to troubleshoot
the modules and look for the load that is pulling the power
supply down. See "Power Supply Troubleshooting." [Power
Supply - look for overwarm devices]
It may appear that self-test didn't begin because the
display is dead and therefore didn't shown anything. To
verify the display is dead, extract the error code over the
RS-232 port instead of from the front panel display. (See
"Retrieving Error Codes using RS-232.")
If the SYS/CTRL microprocessor or related component in
the kernel has failed, self-test will not initialize. See
"Troubleshooting the Digital Kernel." Check the power
supply and crystal oscillator, U13.
If the input line voltage is too low, the SYS/CTRL Power-
On Reset/Power-Fail Detector, U1, might be generating a
POREST* (power-on reset) condition. Alternatively, if for
some other reason the output of the raw dc supply falls
below approximately 8.25 V dc (measured at SYS/CTRL
U301 pin 2 with the power switch on). Locate the low
voltage or missing voltage condition.
Troubleshooting the Device
6
6-35