TROUBLESHOOTING AND REPAIR
POWER SUPPLY
3. If either of the 23.4V or -5V supplies are not at the specified voltage, check the
unregulated supply for both (TP13 and TP1, respectively).
If some of the supplies that are supposed to be off are partially or fully turned on,
check the 37V supply (TP20) voltage.
If the 37V supply is partially or fully on, check the standby switching circuit and the
comparator operation (U3, Q5, R52).
4. Next, switch the power supply on, by connecting the STANDBY line pin to GND
(J6 pin
7,8).
5. Verify all supplies are operating and are within the following specified levels:
a. TP18, 24V supply = 24V (± 5%)
b. TP2, 23.4V supply = 24V (± 5%)
c. TP6, +5.1V supply = 5.1V (± 2%)
d. TP11,+15V supply = 15V (± 4%)
e. TP16, -15V supply = -15V (± 4 %)
f. TP14, -5V supply = -5V (± 5%)
g. TP20, 37V supply = 37V (± 5%)
h. TP21, 30Vsupply = 30V (± 5%)
i. TP15, +5V reference = 5V (± 3%)
6. If all supplies are at the appropriate voltages when in standby, but are not at the
appropriate voltages when the power supply is on, verify that the all standby
supplies are correct.
If the fan supply (24V) is on and the rest of the supplies (with the exception of the
23.4 and -5V) are off, check the current limit circuitry (U2, CR5, CR9, Q4). A short
at either the +15 or the +5.1 could cause the current limit to trip and turn all
non-standby supplies off, with the exception of the fan supply. In this case, verify
that the voltage at TP22 is less than 1V, which indicates a current-limit trip. To
recover from a current limit shutoff, turn off the power supply (to standby
operation) for at least 5 seconds.
7. If only the +5 V reference, +5.1V, +15V, and the -15V supplies are in error, check the
+5V reference circuitry, since it is likely that the fault is with the reference supply,
U1,
CR16.
POWER SUPPLY ADJUSTMENT PROCEDURE 6A-5.
A single adjustment potentiometer is provided for adjusting the voltage output of the
three discrete supplies: the +5.1, +15, and -15V. To adjust these supplies, place a
voltmeter at the +5.1V supply (TP6) and adjust R41 for 5.1V (± 0.05V). Since the
+5.1V, +15V, and 15V supplies are of tracking design, both the +15 and the -15V
supplies should be at 15V ± 0.2V.
6A-5/6A-6
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