General Maintenance
All subsystems
that assert the FAULT LED also assert a local, red LED to indicate
the area that generated the fault. Thus, whenever the instrument fault line is
asserted, you need only remove the top cover and look for the red LEDs inside to
find the location of the fault. The following table lists the circuits that can assert
faults and identifies the LEDs associated with the circuit. (See Figure 4-2 on
page 4-24.) There are also duplicates of the instrument FAULT LED and the audio
fault LED on
the main board (DS940 and DS840.) (See Figure 4-1 on page 4-23.)
Table 4 -5: Circuits that can assert faults
Circuit area Local LED
Fans
DS170, DS270
Audio
DS590 on main
Front Panel
DS252 (between preset 1, 2) on Front Panel
board
CPU DS680
Fan Failures. One possible source of an a sserted FAULT LED is a fan failure.
If the right-side fan fails, then LED DS170 will be lit.
If the left-side fan fails, the LED DS270 will be lit.
The fan failure is sensed through tachometer feedback, thus a fault will be
asserted if the fan is not connected, stalled, or if the tachometer feedback line is
not working correctly.
If one fan fails, the control circuit will increase the voltage and the other fan will
be driven at full speed.
If neither fan is spinning, then check fuse F70 and the dedicated switching supply
that drives them.
If both fans are spinning, but one is showing a fault, swap the fans. If the problem
moves with the fan, then replace the defective fan. If the fault does not track the
swap, then there is a problem on the main board.
The normal voltage to drive the fans (pin 1) varies from about 6 V to 13.5 V in
response to temperature and fan speed.
DSP. The following conditions can assert the FAULT LED from the DSP
circuitry:
Over temperature 2.5 V supply
Over temperature 3.3 V suppl
y
If any of these are in fault condition, the front-panel FAULT light will be lit and
the local, red LED DS550 will be lit. Over temperature faults are reported in the
diagnostic log - so you can look there to see if the DSP is asserting the line and
which supply is the root cause.
4–12 WVR6020, WVR7020, and WVR7120 Waveform Rasterizers Service Manual
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