Tektronix WFM6100 Opt. MB, Service Manual

Page: 43 / 76

General Maintenance
WFM6100, WFM7000, and WFM7100 With Option FP Service Manual
4- 13
resistor R864 on the Main board, and use the oscilloscope to look for a 3.3 V
square wave on the tachometer feedback line. Replace the fan if the pull up is
intact but there is no signal on the tachometer line.
This section describes methods for verifying the proper operation of the
waveform monitor primary power supply.
CAUTION.
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 useful 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, page 4--22). All
should have 5 V on both sides. If not, replace the fuse.
If the supply 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
voltage 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
and 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.
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.
Primary Power Supply
Tests
Secondary Power Supply
Tests