ViewSonic G90FB-4 - Model No. VS10794 - 19” Digital
Controlled Color Monitor - Schematic Diagrams _ Power, Horizontal Out & System control
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SMPS
Before check SW.REG
Variable output: 60V
Constant output: 6.3V, 12V, 83V，180.V, －12V
Adjustment conditions and precautions
Adjustments should be undertaken only on those necessary
elements since most of them have been carefully preset at the factory.
The B+ control block of the SAA4849 has the same behavior as
the TDA4856 with adapted threshold voltages. The circuit allows the user to
choose the trigger edge of the HDRV signal and the polarity of the output stage
via I2C-Bus. The B+ control function block of the SAA4849 consists of an
Operational Trans conductance Amplifier (OTA), a voltage comparator, a
flip-flop and a discharge circuit. This configuration allows easy application
for different B+ control concepts.
Main adjustments:
Power supply Troubleshoot
The horizontal part contains a PLL, which works over the
full frequency range from 25 kHz to 140 kHz. This range can be reduced by a over
and an upper frequency limit (Write Once Registers HPMAX and HPMIN).Via I2C bus
the number of 48MHz clock cycles is sent through the register. The slewing
speed during mode change is also programmable in a write once register (HSLEW) After
the clocks for the HPLL are switched on, the HPLL starts with a fixed free
running frequency of 60 kHz. The H-drive pulses are not active and the start up
procedure is inhibited. The default setting of register bit HCONTROL [0] will cause
the HPLL to slew, not switch. To the free running frequency defined in the I2C
register HPFREE (the default value is also 60 kHz).Independent on H-syncs which
are possibly present. The HPLL will slew to that free running frequency. To
achieve an always defined starting point for the startup procedure, this
procedure cannot be interrupted.
Horizontal scan & output schematic
Micro-controller Section
The micro controller (IC101) core is a 80C51 type. The micro
clock frequency of 12 MHz is derived from the Xtal oscillator, which is running
at 48MHz. The DDC interface is suitable to handle DDC2 by a modified hardware I2C-bus
interface .Standard high current ports,3 ADC pouts with voltage inputs and 4
static standard8 bit DAC outputs (low interference) and one PWM output for
digital control application are implemented. The central processing unit (CPU) manipulates
operands in two memory spaces. These are the 1024byte internal data memory (consisting
of 256 bytes standard RAM and 768 bytes AUX-RAM) and 48K-byte internal program memory.
The program memory of the SAA4849 consists of 48K bytes ROM. The SAA4849P
provides sync. Processing with full auto sync. Capability, a flexible SMPS
block and an extensive set of geometry control facilities. Further the IC
generates the drive waveforms for DC coupled vertical boosters to the TDA8172.
