Front Panel - Hitachi HTD-K185UK Service Manual

•IC800 (MC44608) is a SMPS IC. The switching frequency of this IC is constant. Only the
duty cycle determines the voltage on the secondary side of the transformer and the duty cycle
depends on the feedback current injected into pin 3 (from the secondary side of the SMPS via
the opto-coupler IC803)
• VI pin of IC800 transfers the voltage across C854 to VCC pin internally. This voltage is
used during the start up process. As soon as the IC starts up, this property is disabled.
• IC804 TL431 is a constant current regulator. TL431 watches the 30V output of the
transformer and supplies the required current to opto-coupler (IC803). The LED inside the
IC803 transmits the value of the current from IC804 to phototransistor. Depending on the
current gain of the phototransistor IC800 keeps the voltage on the 30V winding constant.
• MC34167 (IC807) is a power switching regulator and it is used to step down 8V to 5V.
When the device enters stand by mode, transistor Q807 starts to conduct and pulls pin 5
(stby pin) of this IC to ground and this cuts off 5V and 3.3V output of this board.
11.2

FRONT PANEL:

• The VFD controller is a NEC uPD 16311 (IC1). This controller is not a processor, but
does include a simple state machine which scans the VFD and reads the front panel button
matrix.
• The pressed key information is send to MT1379 from pin 5 and pin 6 of IC1.
•IR remote control receiver module IC2 (TSOP1836) sends the commands from the
remote control directly to IC300 MT1379.
• The 16311 also includes RAM so it can store the current state of all the VFD icons and
segments. Therefore, the 16311 need only be accessed when the VFD status changes and
when the button status is read. The MT1379 can control this chip directly using PIO pins. It
sends the commands to IC1 UPD16311 via socket PL301 (on the mainboard).
•Socket PL2 carries the VFD filament voltages (FL1, FL2) and -22 Volts. These three
voltages are sent from the power board (socket PL806).
11.3 I/Os and Back Panel:
•There are
• 2 SCART (input and output) connectors,
• 2 RCA audio jacks for audio output,
• 3 RCA jacks for av input.
• 1 coaxial digital audio output,