Troubleshooting The Power Supply; Troubleshooting The Digital Section - Fluke 39 Service Manual

5-4. Troubleshooting the Power Supply

After pressing o, check the power supply voltages against the supply range values in
Table 5-2.
If the power supplies do not come on, the problem could be with the power-on circuit
itself. The following technique can be used to force the power supply on, even when the
DSP or power-on circuit is defective. Refer to Figure 5-1 for test point locations in the
following steps.
1. To ensure the Tester is not drawing too much current, remove the batteries and
connect a 5-volt supply that indicates supply current between +VBT and -VBT.
2. Turn on the power supply.
If the current draw with the Tester power off is greater than 0.5 mA, check the power
supply capacitors C48 and C61 for shorts.
3. Short SW1 and SW2 together with a jumper while monitoring the amp meter on the
supply. If the current draw exceeds the High Limit level in Table 5-1, immediately
remove the power from the Tester and isolate the excessive current draw using
appropriate troubleshooting methods.
Tester Condition
Start-up Current
Normal w/o Backlight
Normal with Backlight
If the Tester powers up within the current limits of Table 5-1, you can check the power
supply voltages against the voltage range specified in Table 5-2.
Supply Name
VCC
VDD
VSS
VEE
VREF
-22 VDC

5-5. Troubleshooting the Digital Section

The digital section of the Tester is made up of the digital kernel, keypad, display, and
optical interface. Fault isolation procedures for each of these areas are listed below.
Table 5-1. Power Supply Current Limits
Low Limit
130 mA
70 mA
115 mA
Table 5-2. Power Supplies
Measure
From:
Jct. of C63 & T1
U15-1
U17-4
U25-7
U14-9
U25-4

Troubleshooting the Power Supply

High Limit
Supply Range
To:
Comm 3.13V to 3.47V
Comm 5.75 to 5.25V
Comm -7 to -5V
Comm -18.5 to -15V
Comm 2.1016 to 2.1292V
Comm -23.32 to -20.68V
Troubleshooting
200 mA
110 mA
165 mA
5
5-5