Zenith DVB318, Service Manual

Page: 14 / 68

3-5
Check the followings
1) Check the video output mode. if the output
mdoe is progressive - on, there is no compos-
ite signal.
the output mode should be changed to
progressive - off
2) Check the buffer IC and MPEG, and then
replace.
175 Ohm
Composite out
34 pin
IC403
23Pin
STI5589
(MPEG)
buffer
DC 0V
15.7 Khz
DC0.3V
31.3 Khz
Composite signal is normal --> Screen display OK Composite signal is abnormal -->there is no screen on TV
8. Checking the Video Signal
81
82
IC501
MPEG
DSP-RST
PC[o]
IC202
DSP IC
IC203
MOTOR
AMP IC
Let’s look over the initial step of DSP
1) First. DSP IC receive the DSP - Reset from
MPEG
2) This reset signal get DSP initialized and DSP is
ready to do first step for servo
3) PC[o] from DSP is the test signal for checking
the PLL- loop
4) after checking the PLL-loop, the second step is
followed. the second step will be explained on
next page…..
if PC[o] doesn’t appear, check DSP and
replace.
/DSP-Reset
Vcc(3.3V)
50ms
DSP Reset period
PC[o]
9. Checking the first step of servo (1)