Acer AM501, Service Manual

Page: 35 / 85

31
6.8.3 Power Saving Control Switch
Q940 is an ON/OFF switch of 13VS, when received a suspend signal (PS1 from high to low) which
comes from
ų -p, Q940 will turn off making the monitor to go to suspend mode.
U900 be control by H-Sync. And V-Sync. detective CKT. When H-Sync. and V-Sync. disappear , U900
provides Vref to U901 PIN2, the power supply slut - down and unlatch to enter OFF mode. The power
LED will flash naturally in this time.
6.8.4 Boost Mode Power Conversion CKT (The B+ Generator)
It consists of boost power stage, output rectifier and filter, driver CKT and PWM signal comes from
U401.
a. Q505 acting as a power transistor controls the energy flow through L501and D508 combining with the
output capacitor C513 to generate a voltage higher than the input to supply the B+ voltage to monitor.
b. There is a close loop to control the B+ voltage so as to regulate HV of the CRT. The feedback signal
comes from the H.V. bleeder of the FBT then sends to U401 to regulate the HV output.
6.8.5 Synchronizing CKT:
There is one sync signal comes from FBT pulse to synchronize the working frequency of U901.
6.8.6 Protection CKT
Under short CKT condition for each output, the Vcc of U901 will be removed and turn off all the outputs.
When short CRT condition is released, Power will restart automatically.