Improper line voltage may cause one or all of
the supply voltages to be off.
All the low voltage power supplies are de
pendant upon the —150 volt supply for regula
tion, and consequently, a change in the regula
tion point of all the supplies is indicative of a
defective —150 volt supply. If the output voltage
of the —150 volt supply is off by only a small
amount, it may be possible to readjust the —150
ADJ control for the proper voltage. In any event
it will be necessary to recalibrate the instrument
according to the procedures given in the Recali
bration section of this manual.
In case of the failure of a single power supply
to regulate properly, check the following:
1. Line voltage
2. Transformer voltage
3. Output voltage of the rectifier
4. Tubes or transistors
5. Loading
Important power supply voltages are marked
on the power supply schematic diagram. These
voltages may be used to perform checks on the
power supply operation. One cause of improper
regulation by a power supply is incorrect load
ing of the supply. To check power loading, shut
off the power and check the resistance of the
power supply output bus to ground. The —150-
volt bus should read approximately 5,000 ohms,
the + 100-volt bus approximately 5,000 ohms,
and the +350-volt bus approximately 11,000
ohms.
If none of the preceding checks determine the
cause of the trouble, the cause of the improper
regulation is probably a change in value of one
or more of the resistors or capacitors composing
the voltage divider networks. The resistance
networks in the grid circuits of V746B, V666B,
and V636A and the base circuit of V644 are
particularly critical since they determine the
output voltage of their respective power supplies.
Use resistance checks to isolate the defective part
or parts. The following information may be used
as quick index to troubleshooting the Low-Volt
age Power Supply.
If the output voltage is high with excessive
ripple, check:
1. For high line voltage
2. The amplifier tubes and transistors (V746,
V666, V636, V644, and V634).
3. For insufficient loading
If the output voltage is high with normal rip
ple, check:
Fig. 5-4. Low voltage power supply test points.
1. For proper resistance values in the dividers
(R751 and R753; R671 and R673; R621, R622,
and R623; and R648 and R649)
If the output voltage is low with excessive rip
ple, check:
1. For low line voltage
2. The series regulator tube (V747, V757, V677,
V637, or V647)
3. For excessive loading
4. Open or leaky filter capacitors
5. Rectifiers (V722, V652, V602, or SR642)
If the output voltage is low with normal ripple,
check:
1. The resistance values in the dividers
2. The capacitors across the dividers
If the output voltage is normal with excessive
ripple, check:
1. Filter capacitors at the output of the recti
fiers and at the regulated output
2. AC bypass capacitors in the grid circuits of
the regulator amplifiers
3. Regulator amplifiers screen grid circuits
®
5-8
MAINTENANCE — TYPE 502
To Next Page
Loading...
