Sony CTV-25R1 Manual page 107

protect itself. The Timer/Standby light blinks two times, pauses and
repeats to indicate the failure.
If flyback (FBT) pulses were abnormally high, perhaps as a result of
an open resonate capacitor (C508 in this set), the TV would similarly
shut down. Higher than normal FBT pulses result in a high DC volt-
age that also grounds the horizontal pulses at IC301/pin 18. The
loss of horizontal pulses is detected and data is sent from IC301/pin
35 to IC001/pin 37 for the TV to shut OFF. The Timer/Standby light
continues to blink two times, pauses and repeats after the failure.
3. White Balance Failure – Jungle IC301 initiates CRT drive and moni-
tors CRT cathode current at pin 21. The amplitude of the three IK
pulses that return to IC301/pin 21 represent the level of red, green
and blue CRT cathode emissions. Their amplitudes are used to white
balance the picture while the TV is ON.
This IK circuit is designed to look for three IK pulses returned from
the picture tube. If IC301 detects a missing IK pulse within two sec-
onds after the set is turned ON, the video is blanked (muted). The
two seconds allow time for the picture tube to warm up.
This blanking state is relayed as data from IC301/pin 35 to IC001/pin
37. IC001 causes the Timer/Standby light to blink five times, pause
and repeat. The set remains ON during this video failure, so the
sound is still present.
When there are multiple failures, the two blinking light failure has a higher
priority over the four blinking light failure. By the same logic, the four
blinking light failure has a greater priority than the five blinking light fail-
ure. For example, if multiple failures caused all of the two, four and five
blinking light failures to be stored in memory, the Timer/Standby light
would blink two times, pause and repeat when the TV shut down. The
number of failures has nothing to do with how many times the light blinks.
Display
By using the TV's remote control, you can access this failure information
stored in memory. Once IC001 receives the self-diagnostic access com-
mand at pin 12, IC001 powers ON the TV. The failure information from
IC001 is sent to the Jungle IC301 as On Screen Display (OSD) video
levels.
A "OSD Blk" signal accompanies the OSD video levels from IC001 into
IC301. This analog input voltage at Jungle IC301/pin 29 is used to darken
(blank) the main RGB picture signal at the instant the OSD character is
103
to appear and enable the OSD. Since IC301/pin 29 is an analog input,
0Vdc input leaves the main picture at normal brightness. 2Vdc input
reduces the picture to half brightness and 5Vdc blanks or mutes the
picture.
Main Picture Brightness Control with OSD
Voltage at IC301/pin 29
0 Vdc
2Vdc
5Vdc
The following waveform was taken with the self-diagnostic page displayed
on the TV. The waveform shows that the YM/OSD BLK signal is at an
average level of 2.0 volts for the main picture brightness reduction. There
are peaks of the YM/OSD BLK signal that rise to 5Vdc to mute the main
picture. These peaks correspond to the self-diagnostic OSD characters.
By muting the main picture at this time, the OSD letters appear on the TV
screen without interference from the main picture.
CH 1
CH 2
Channel 1 =IC301/pin 29 – OSD Blk signal. 2V/div.
Channel 2 =IC301/pin 31 – OSD green signal input. 0.5V/div.
Time base = 2msec/div.
While the main picture is at half brightness, the OSD self-diagnostic page
is displayed at normal brightness and appears as an overlay to the main
picture.
Brightness level
Normal
Reduced to half
Dark – main picture muted.