Speco Technologies VM-1201 - Manual (Page 11)

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Flyback generator ：
‧ U301 pin6 is the output of the flyback generator that when driven, jumps from low to high
condition C305 transfers the jump to pin3
Vertical size control ：VR301, R312, R308.
2.5 Horizontal Deflection Block
Horizontal drive buffering
：Driving source-U401 pin11. Driving transistor-Q40, to pull high the
driving waveform to drive the Q401(MOS FET).
Horizontal deflection ：Horizontal Output transistor-Q401; Load-Yoke inductance and C414 ;
D401, High Voltage generation-flyback transformer .
3 Troubleshooting Instructions
‧ This chapter describes possible failures of the monitor with corresponding check/correction
actions, and guidelines for safe operation and service of the monitor.
3.1 No Display, No Power
3.1.1 First of all, turn power off, use multimeter to check Q901, and R904, replace if bad. Turn
power on after that.
3.1.2 Check DC voltage across C906. If no voltage or voltage too low, check and fix the following
components ：AC receptacle poor contact, fuse F601 broken, power switch malfunction, or
bridge diode D901 bad
3.1.3 Check voltage on U901 pin 7 for start up condition ：If voltage on U901 pin 7 reaches the start
up voltage(around 15 to 17.5V), U901 UC3842 will start to work and output 5V at pin 8. If
voltage on U601 pin 7 is too low, check and fix following circuits ：start up circuit R914,
and C914.
3.1.4 If no output pulses at U901 pin 6, check and replace U901.
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