Panasonic BT-M1950Y Service Manual page 102

ts l·Ml~oUY
8. On-screen signal converter (OSDC signal generator)
The MPU OSD orange signal selects between the orange color level (R:G:B
=
1 :0, 7:0) ratio setting circuit and the on-
screen TTL level RGB output 0/52 Vp-p setting circuit.
When the OSD orange signal is High, 0207, 0208 and 0209 switch on. The IC102 on-screen IC pin 12, 13 and
14
outputs are 0.52 Vp-p. As a result, the R202 : R205 : R217 resistance ratio sets the T connector OSD R : OSD G :
OSD B
=
0.52 Vp-p : 0.36 Vp-p :
O
Vp-p, which is the on-screen orange color setting at the factory. The display on the
screen is controlled by the video processor IC402 of the signal PB ASS'Y from the OSD enable signal from IC108 pin
6. The color can be changed by selecting the service mode. If changed, the on-screen IC102 pin 12, 13 and 14 outputs
are not 0.52 Vp-p.
When the Blue Check button is pressed, the blue check signal from the MPU is sent to sync selector IC106 pins 13 and
14. The negative logic -blue up signal from pin 12 switches 0210 off and sets the OSD N signal level from 0.52 Vp-p to
0.62 Vp-p.
When the OSD orange signal is Low level (changeable in the service mode), 0207, 0208 and 0209 are off. As a
result, R202 + R211, R205 + R213, and R217 + R215 are respectively set to 290 ohms and the on-screen IC102
pin 12, 13 and 14 outputs go directly to the T connector OSD R, OSD G and OSD B.
The on-screen color is set by the service mode control block C03. Nos.
O -
7 are when the OSD orange signal is High
level, while Nos. 129 - 139 are when the OSD orange signal is Low level. In Table 8-1, the R, G, B column indicates
the No. column in binary form. The lower 3 digits indicate presence or absence of the on-screen IC102 pin 12, 13 and
14 outputs. For example, since C03 is set to 7 at the factory, R, G, Bis
1,
1, 1 and the on-screen IC102 pin 12, 13 and
14 output signals are all present.
No. Display color R,G,B No. Display color R,G,B
0
Black (blue check: dark) 0,0,0
129
Blue 1,0,0,0,0,0, 1
1
Black (blue check: bright) 0,0, 1
130
Green 1,0,0,0,0, 1,0
2
Green (blue check: dark)
0,1,0
131
Cyan
1,0,0,0,0, 1, 1
3
Green (blue check: bright) 0, 1, 1
132
Red 1,0,0,0, 1,0,0
4
Red (blue check: dark)
1,0,0
133
Magenta
1,0,0,0, 1,0, 1
5
Red (blue check: bright) 1,0, 1
134
Yellow 1,0,0,0, 1, 1,0
6
Orange (blue check: dark) 1, 1,0
135
White 1,0,0,0,1,1,1
7
Orange (blue check: bright) 1, 1, 1
136
Black 1,0,0, 1,0,0,0
Table 8-1
9. Reset circuit
In event of power supply abnormality, the reset circuit functions to quickly inform the MPU and avoid damage to the
system.
Reset operates when cutoff of the + 12 V power supply line is detected. Quick detection is possible since the + 5 V and
+
8 V power supply lines are regulated by the
+
12 V power supply line. The function is important since sudden cutoff
or failure of power can cause abnormal operation of the signal PB ASS'Y video processor IC.
Normally, the MPU pin 16 (-RST) is High level and goes Low during reset. Reset may not operate unless the Low level
is below VCC x 0/2 V. The MPU is operable at VCC
=
2.2 V (block 1 M) and -RST below 2.2 x 0.2
=
0.4 V is
required. If the reset voltage is higher than the specification, MPU operating error can destroy the EEPROM data.
10. Clock oscillator
The 8 MHz clock signal is applied to the MPU pins 12 and 13.
11. Power supply lines
Power supply lines are supplied via the signal PB ASS'Y pins 7 ( + 12 V), 5 ( + 5 V), 6 (GND) and 8 (GND). In order
to avoid MPU output interference, separate power supply lines (digital + 5V and GND, and analog
+
5 V and GND)
are provided on the MPU PB ASS'Y (source same as U connector pin 5).
-102-