Tektronix WFM700 Series, Service Manual

Page: 168 / 194

Troubleshooting
4- 34
WFM700 Series Waveform Monitors Service Manual
Use this troubleshooting tree to help diagnose instrument power-up problems or
failures. You can also start with this tree if unsure of the nature of the problem.
No
Power on the
instrument.
Can you
hear the power supply relay
click when the ON/STBY
button is pressed?
Is
the +5 V LED
DS5473
on?
Check Power cord and power source.
Check that the power supply control cable
is properly connected at both ends and is
not damaged.
Check for +5 V on pin 1 of power supply
cable at J271 and at TP373.
If all OK, replace power supply module.
No
Yes
Yes
Check that the cables between Main Interface board and the Front Panel
module are properly connected at both ends and are not damaged.
Check that the wide flex-cable on the left side of the Front Panel module is
properly connected and not damaged.
Do the
ON/STBY and FAULT LEDs
indicate a status other than
normal operation (refer to
the LED fault
table)?
Yes
Does
DS390 (POWER
ON LED) switch on and off
when ON/STBY switch is
pressed?
Any
problems found?
Can you hear the power
supply relay
click?
No
Yes
No
Remove the modules from slots 4
and 5 to gain access to J470.
Use a jumper to momentarily short
the two pins of J470 together.
Do you
hear the power supply relay
click when shorting the pins
together?
Yes
Replace the Main
Interface board.
No
Replace Power
Supply module.
The power button contacts should short the pins of
J592 together. Trace connections from J592 to the
power button to identify the faulty cable or module.
Pin 34 of J390 is connected to the power button
through a ribbon cable to J150 on the Front Panel
Assembly, then through pin 4 of the flex cable from
J680 to the Left Keyboard. The ground connection
to the power button originates on the Main Interface
board, connects through pin 35 of the ribbon cable
on J390, and pin 5 of the flex cable on J680.
Proceed to the LED Fault Troubleshooting
Tree 1 on page 4--35
Separate the Front Panel assembly from the
main chassis. Leave all cables attached except
for J890 on the Main Interface board.
Use a jumper to momentarily short the two pins
of J592 together.
Does
DS390 (ON/STBY) switch
on?
Check that U790 is seated in its
socket. If DS390 is still not on,
replace Main Interface Board.
Yes
If problems persist, refer
to Check for Problems on
page 4--27.
Yes
No
No
Figure 4- 13: Primary troubleshooting procedure
Power Troubleshooting
Tree