Troubleshooting The Power Supply - Fluke Autoranging CombiScope PM3370B Service Manual

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8.8

TROUBLESHOOTING THE POWER SUPPLY

WARNING:
The table below indicates the output voltages, currents and power figures delivered by the power
supply. To determine whether a certain fault condition is initiated by the power supply itself or by the
connected oscilloscope circuits, a dummy load is listed in the table. The table gives also an example
of the resistor types that can be used to compose the dummy load. The resistors and connector
(ordering number 5322 267 70308) that fits on connector X1002 can be ordered at Consumer
Service.
Supply volt-
age
+5 V
-5.2 V
+12 V
-12 V
+18 V
-18 V
+58 V
-58 V
+10 Vref
6.3 Vac
-2.2 kV
+14.5 kV
Another way of fault location is the use of the extension board with ordering code 5322 218 61479.
On this board there is a jumper that can be removed to switch off the EHT-converter. For safety
reasons it is strongly recommended to use this feature.
The current drawn from a certain supply voltage can be measured after having removed the series
choke and connecting a current meter instead of it. The chokes are L1273 (+5 V), L1201 (-5.2 V),
L1202 (+12 V), L1203 (-12 V), L1204 (+18 V), L1206 (-18 V), L1208 (+58 V) and L1209 (- 58 V).
On the power supply there are many parts that carry dangerous high voltages.
Some of these voltages remain some time after disconnecting the unit from the
mains. Therefore, it is recommended to wait at least five minutes after having
disconnected the unit from the mains, before removing the unit. If working on
the power supply unit under live condition cannot be avoided, it must be done
by a qualified technician who is aware of the dangers involved. The use of an
mains isolation transformer is strongly recommended.
Current Substitution
drain resistance
3000 mA 1.7 Ω
1750 mA 2.9 Ω
6.8 Ω
1750 mA
8.3 Ω
1450 mA
550 mA 32.8 Ω
92.5 Ω
195 mA
966 Ω
60 mA
725 Ω
80 mA
9 mA 1100 Ω
26.3 Ω
240 mA
700 uA 3.1 MΩ
50 uA 290 MΩ
CORRECTIVE MAINTENANCE PROCEDURES
Dissipated Dummy load resistors
power
15 W 5x 10Ω/4W (4822 112 21054) in parallel
8.7 W 3x 10Ω/4W (4822 112 21054) in parallel
21 W 3x 22Ω/7W (4822 112 41063) in parallel
17.4 W 3x 27Ω/7W (4822 112 41065) in parallel
10 W 3x 10Ω/4W (4822 112 21054) in series
3.5 W 2x 47Ω/4W (4822 112 21072) in series
12.1 W 2x 470Ω/7W (4822 112 41098) in series
4.7 W 330Ω/4W (4822 112 21094) and
390Ω/4W (4822 112 21096) in series
0.1 W --
1.5 W --
1.55 W --
0.7 W --