Fluke 39 - Troubleshooting the Power Supply; Troubleshooting the Digital Section

Troubleshooting
Troubleshooting the Power Supply
5
5-5
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.
Table 5-1. Power Supply Current Limits
Tester Condition Low Limit High Limit
Start-up Current
Normal w/o Backlight
Normal with Backlight
130 mA
70 mA
115 mA
200 mA
110 mA
165 mA
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.
Table 5-2. Power Supplies
Supply Name
Measure
Supply Range
From: To:
VCC
VDD
VSS
VEE
VREF
-22 VDC
Jct. of C63 & T1
U15-1
U17-4
U25-7
U14-9
U25-4
Comm
Comm
Comm
Comm
Comm
Comm
3.13V to 3.47V
5.75 to 5.25V
-7 to -5V
-18.5 to -15V
2.1016 to 2.1292V
-23.32 to -20.68V
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.