Read Sharp 28JF-74H (serv.man2) Service Manual online
50Hz Widescreen Colour Television – GA20 Chassis
Sharp Electronics (UK) Ltd
Technical Support
Issued June 02
Page 16
pins 47(VSUP
AF
) and 108(VSUP
AB
)
The horizontal output pin is a open drain configuration, therefore the +5v is
applied to pin76 via a pull-up resistor R1038.
applied to pin76 via a pull-up resistor R1038.
+3.3v
Present when the CTV is running and is derived from the +5v by IC1007. It is
applied to pin 77(VSUP
applied to pin 77(VSUP
D
).
R
ESET
/W
ATCHDOG
C
IRCUIT
The reset and watchdog circuits are internal with an external pull-up resistor R1060 at pin 117
(RESQ) connected to the +3.3v standby supply. The reset level is ‘Active Low’. This RESQ port is bi-
directional, therefore it has the capacity to act as a reset command to any external device that
requires a reset, this feature is not used. Instead the port 15 (pin 35) has been configured as a reset
command (RES), connected to the +5v rail via pull-up resistor R308 for the MSP (IC301) ‘Active Low’.
I
2
C
B
US
There are two I
2
C bus ports configured on this device. Pins 118 and 119 are the dedicated I
2
C port
with pull-up resistors R302 and R306 to the +5v. This I
2
C bus communicates between IC1001, IC301
(MSP), IC201 (IF) and the tuner. The second I
2
C bus is configured by the software to use IC1001
ports 36 (pin 80) and 37 (pin79). This allows communication between IC1001 and IC1003 (NVM).
There are two pull-up resistors to the +5v rail, R1034 and R1035.
Note
There are two pull-up resistors to the +5v rail, R1034 and R1035.
Note
When writing data directly to the NVM from a PC remove R1036 and R1037.
V
ERTICAL
P
ROTECTION
Vertical fly-back is fed to IC1001 pin 94. The IC is looking for a pulse >2.5v on this pin. If it cannot
detect the negative going edge then the RGB output will be blanked.
S
AFETY
(Pin 95)
This pin is normally zero. If it increases above 1.8v the RGB drive is blanked. If the voltage continues
to rise above 3.8v then horizontal drive is stopped, until the voltage at IC1001 pin 95 has decreased
to <1.8v.
Q1012 turns on and forward biases D1017 which will take IC1001 pin 95 high. This ensures that the
line oscillator is turned off. Therefore, there will no possibility of any supplies from the line stage that
could possibly cause noise.
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