General Maintenance
Primary P ower Supply
Tests
This section de
scribes methods for verifying the proper operation of the waveform
monitor primary power supply.
WARNING. Some parts of this test may require removing the insulating safety
shield. To avoid personal injury, be careful not to contact the circuitry while the
shield is removed. Be sure to replace the shield as soon as possible to prevent
injury.
The main power supply accepts 100 to 264 VAC and outputs 5 VDC. The output
voltage at the supply must be between 4.9 and 5.3 V for correct operation. On the
main board
, the common 5 V supply must be between 4.80 and 5.25 V.
There is also a green LED, DS232, that will be lit if some 5 V power is present.
This is a u
seful indicator, but does not insure that the voltage is within tolerance.
If the power supply output is correct, check the seven fuses in the 5 V system near
the main
board power connector J14. (See Figure 4-1 on page 4-24.). All should
have 5 V on both s ides. If not, replace the fuse.
If the s
upply output voltage is zero, then check the input circuit. The voltage
should be the same at the line cord, at the input to the power supply, and on both
ends of the fuse on the input to the supply. If the input voltage is correct while
the output is not, replace the supply. If the input voltage is not correct replace the
element in the chain that is not passing the AC input.
If the voltage at the output of the supply is not zero, but still not correct, check
the input voltage. If the input voltage is in the correct range, then disconnect the
output of the supply from the main board and recheck the output voltage. If the
vol
tage is still not correct then replace the power supply.
If the no-load output voltage is correct, then reattach the cable to the main board
an
d measure the current by clamping the ammeter around all the red wires. If
the current is less than 14 Amps, and the voltage is still bad, then replace the
power supply. If the current is more than 14 Amps, then remove module boards
and recheck the current. If it is still high then replace the main board. If not
then test with one option board at a time to find the one with excess current and
replace that board.
Secondary Power Supply
Tests
There are multiple secondary supplies that are derived from the main 5 V supply.
Be sure all seven 5 V fuses are good (as noted in Primary Power Supply Tests)
before checking the secondary supplies.
First, check the LEDs near the power connector, J14. Green LED DS232 indicates
thereissome5Vfromthemainsupply.
4–14 WFM6120, WFM7020, and WFM7120 Waveform Monitors Service Manual
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