Heater Voltage Regulator; Troubleshooting Heater Voltage - Sony CPD-420GS Training Manual

Heater Voltage Regulator

Heater filament voltage is developed by the +8V DC supply to IC604/1 (I).
During 'Active On' mode, IC1001/8 (N Board) outputs the "HEATER" con-
trol line H (+5V) which is routed to IC604/4 (VC) to enable the +6.3V DC
Heater supply voltage output at pin 2.
During 'Standby/Suspend' mode, the power supply is operated at reduced
voltages. As a result, the input voltage to IC604/4 (VC) is +5.5V DC. The
output from IC604/2 is also reduced to +3.2V DC keeping the heaters of
the CRT active on during the power saving function. This allows the CRT
to quickly display the information or video during the 'Standby/Suspend'
to 'Active On' transition.
During 'Active Off' mode, IC1001/8 (N Board) outputs a L (0V) to IC604/4
(VC) disabling the +6.3V DC Heater supply voltage.
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Troubleshooting Heater Voltage

A loss of Heater Voltage will result in a no picture condition. During 'Active
On' mode, confirm IC1001/8 (N Board) outputs 'HEATER' control line H
(+5V) to IC604/4 (VC) to enable the +6.3V DC Heater supply voltage.
Also check for shorts or an open on the A Board and the CRT.