Shutdown Circuitry - Philips PTV500 series Service Manual

Regulator, Q401. Regulation is accomplished by monitoring the
130V Source via a voltage divider network. This feedback refer-
ence voltage is sent through the Control IC and the Output
Voltage Regulator Opto-lsolator to the Dual Controller IC. The
130V Source can be adjusted by changing the reference volt-
age via the 130V Adjust potentiometer.
Cable connections and voltage check points for the Power
Supply are shown in Figure 10. To assist in making connec-
tions, plugs and jacks have been color coded in the 1993
Projection Television. Note, Jack 402 has a yellow plug and
Jack 404 has a red plug. Another feature is that all boards have
been coded with a letter. The Signal/Deflection/High Voltage
board is the "A" Board and the Power Supply board is the "P"
Board (see Figure 18). The 404 cable end that connects to the
"A" Board is labeled "A404" and the other end of the cable that
connects to the "P" Board is labeled "P404". This labeling
method will help prevent incorrect connections.
All voltages from the Power Supply can be checked at the jacks
of either the "P" Board or the "A" Board. Also shown in Figure
10 are the Scan Derived voltages.
Shutdown
Circuitry
The High Voltage circuitry, even though it is located on the main
chassis PCB, is separate from the Horizontal circuitry (Figure
11). The High Voltage is phase locked to the Horizontal signal
via the "Horiz Pulse" as input through Q900. This pulse is
applied to IC900-3, the High Voltage Sync Processor. Its output
drives the High Voltage stages to the HV Output Transformer,
T900. Here, the High Voltage and Focus/Screen Voltage is
developed. A Shutdown/Phase Sense winding from T900
develops the signal used for phase correction (input to IC900-8)
and Overvoltage Shutdown (input to IC902-1). Beam Current is
monitored from the bottom of the Diode Stack, Pin 10
(Aquadag).
The PTV will go into Shutdown when the High Voltage or Beam
Current increases beyond the designed safety limits. There are
four basic shutdown areas; too much High Voltage, too much
Beam Current, no Horizontal Scan, and no .Vertical Scan. In the
case of no Horizontal or Vertical scan, beam current must be
stopped quickly to prevent damage to the CRT's phosphor.
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