Tektronix WFM8200, Service Manual

Page: 52 / 85

General Maintenance
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 the red wire. If the
current is less than 20 Amps, and the voltage is still bad, then replace the power
supply. If the current is more than 20 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
fi nd 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 eight 5 V fuses are good (as noted in
Primary Power Supply Tests )
before checking the secondary supplies.
First, check the LEDs near the rear left side of the instrument. Green LED
DS19 indicates there is some 5 V from the main supply.
Next, check if any of the three Red LEDs (DS5, DS6, or DS7) are on. These
indicate failures on the general 5 V, general 3.3 V, and processor 1.5 V supplies,
respectively. If these are lit, the most likely causes are the fuses near J14, but if
those are all OK replace the main board.
Next, check the secondary supplies as shown in the table. (See Table 4-5.) Each
supply has a test point in the rear left corner of the Main board. (See Figure 4-1 on
page 4-20.) If any supplies are out of range, replace the main board.
Table 4-5: Main board secondary supplies
Nominal (+V) Allowed range (+V) Labeled as
1.8 1.7 to 1.9 + 1.8 V
Fan 5 to 13.5 FAN_PWR
+5 4.75 to 5.25 + 5 V
3.3 3.2 to 3.4 + 3.3 V
2.5 2.4 to 2.6 + 2.5 V
1.5 1.4 to 1.6 + 1.5 V
1.0 0.95 to 1.05 + 1.0 V
+5A 4.75 to 5.25 + 5 VA
-5A -4.75 to -5.25 – 5 VA
1.2 1.2 to 1.4 + 1.2 V
Check the Audio supplies on the Audio board (if an Audio board is installed).
(See Table 4-6 on page 4-13.). The test points are available with the board
installed. (See Figure 4-2 on page 4-21.).
4–12 WFM8200 and WFM8300 Waveform Monitors Service Manual