HP 85662A, Troubleshooting And Repair Manual

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High Voltage Power Supply (85662060232 and
Circuit Description (Serial Number Prefixes: 3004A and Above)
V Regulator
The V Regulator is the same as the previous version of this board assembly
(85662-60101) except that V dc voltage regulated by VR2 was V dc in the previous
version. This voltage is always present whenever the 85662A is plugged in. It is used to
power the thermal shutdown section and HPON (High=Power On) circuit. The main
V is turned off when in thermal shutdown or when HPON is false. Refer to
V
Regulator for additional information.
-15 V Regulator
The -15 V regulator is identical to the one used on the previous version of this board
assembly (85662-60101). Refer to
V Regulator for additional information.
Thermal Shutdown
The thermal shutdown and HPON (High=Power On) control section is nearly identical to the
previous version of this board assembly (85662-60101). The difference is that R42 and R45
were changed from 6.19 to 11 to accommodate the change in power supply voltage
from V to V. This change maintains the same voltage threshold for the HPON
signal. Comparator is half of a dual comparator. Refer to V Regulator for
additional information.
High Voltage Power Supply
The High Voltage Power Supply provides the operating voltages for the CRT. These
voltages are: 6.0 V ac for the filament, -2400 V dc for the cathode,
V dc for the post
accelerator and approximately 400 V p-p for the High Voltage Regulator board to
provide dc restoration to the grid and focus signals.
The High Voltage supply is made up of High Voltage Module interconnected through
the High Voltage Regulator and the Display Motherboard to High Voltage
Power Supply that contains the V and -15 V power regulators and the drive circuits for
the High Voltage Module. The High Voltage Module consists of a transformer that generates
the ac voltages and various rectifier and multiplier circuits to produce the dc voltages.
The transformer primary and form a resonant tank circuit at about 30 Energy
is synchronously pumped into the tank circuit from the High Voltage Power Supply and
the cathode voltage is fed back from the
board through to form a regulated
feedback loop (HV FEEDBACK).
The power to run the high voltage supply is pre-regulated by a three terminal regulator,
to V dc. This pre-regulation helps save some heat dissipation in the drive portion of the
HV supply. supplies the average power for the supply, while and supply
much of the pulse of current to pump the resonant tank. goes into current limit at
approximately one amp during the pump pulse (peak current about 3 amps) then recharges
the and before the next pulse.
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