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CIRCUIT DESCRIPTION
Figure 2 is a simplified diagram of the main Power Supply used in the ZP94/95 series Projection Television
chassis. The primary control element of the power supply is IP01 (the Switching Regulator IC), in conjunc-
tion with transformer TP91. These two components, along with the supporting circuitry, comprise a closed
loop regulation system. Unlike previous Pulse Width Modulated (PWM) Switch Mode Zenith power
supplies, the regulation system in the this chassis utilizes Frequency Control Modulation with an operational
frequency of 85KHZ to 100KHZ, corresponding to full load and no load conditions, respectively. Primary
regulation is provided by IP03, IP04 and into IP01, regulating the switching frequency at pin (3) of I901 via
pin 1, the regulation input to the IC. Two primary secondary voltages are developed that are needed to
sustain run and maintain regulation; Run Voltage generated from pin (8 and 9) of TP91, +120V used for
regulation and powering the regulation circuitry.
POWER SUPPLY FREQUENCY OF OPERATION DURING RUN
When the Horizontal deflection is in operation, the power supply frequency fluctuates in accordance to
screen brightness, causing differing demands for High Voltage replacement. The normal operational range
for the power supply is between 80 kHz to 100 kHz. The lower the frequency, the higher the current
supplied to the load. During Stand-By, it operates at 200KHz.
GREEN LED:
120V Deflection B+ DP29
The Deflection B+ 120V supply is generated from pin (13) of TP91. This output is rectified by DP11 and
filtered by CP17. This supply is routed to the Horizontal Drive Circuit and the High Voltage generation
circuit. This voltage is what illuminates the Green Visual Trouble Shooting LED, DP29.
ZP-94/95 CHASSIS L.E.D. (VISUAL TROUBLE DETECTION) DIODES
DEFLECTION PWB 1 GREEN L.E.D.s and 1 RED L.E.D.
ALL GREEN
L.E.D.s
120V Deflection B+
RP29
RP28
DP29
G
RP42
IP01
Driver/Output
IC
IP04
4
Osc B+
4
IP04 Regulator
Photocoupler
DP37 is a RED L.E.D.
Off = No I901 B+
On = I901 B+ OK
3
1
2
Vcc
Run
24.2V
DP37
R
Start Up
RP02
RP03
1
IP03
2
IP03
Regulator
DP0
2
POWER SUPPLY SHUTDOWN EXPLANATION
This chassis utilizes IP01 as the Osc.\Driver\Switch for the Deflection power supply, just as the previous
chassis have done. This IC is very similar to the previous versions, however it does differ in Frequency,
(described previously). The Shutdown circuit, (cold ground side detection), is used to turn off the Relay
S901 via the following circuit, QP01 (the Shutdown SCR), Connector PQD2, Q911 the Relay Driver and
the Relay S901. The Power Supply utilizes a Shutdown circuit that can trigger QP01 from 14 input sources.
When any of these inputs cause a high on the gate of QP01, the relay disengages, disabling the deflection
power supply. All of the Power Supply Shutdown circuitry can be broken down into the following groups;
