Summary Of Shutdown Circuits - Toshiba TP43H60 Service Training

Summary of Shutdown Circuits

Toshiba incorporates an elaborate shutdown cir-
cuit in every projection television for customer
safety and to prevent damaging the television if a
failure occurs. If the shutdown circuit engages,
neither the front panel power switch, nor the re-
mote power switch operates the TV. Refer to Fig-
ure 1. Although the standby power supply remains
operational, power relay SR81 disengages to cut
the power to the main supply and the power LED
in the front of the TV blinks. To reset the shut-
down circuit, the AC power cord must be un-
plugged. If the power LED blinks, but the relay
still operates or remains closed, the television is not
AC Line Plug
SR81
Stand-By Power
Supply
11V
activates relay.
Q843 and QB30
Main Power Supply
Shutdown Operation
in a shutdown condition. In this scenario, the blink-
ing LED indicates that the problem is related to the
microprocessor's serial clock and data lines. If the
relay doesn't energize or remains closed and the
power LED remains steady, the television is not in
shutdown. The main indicator of a shutdown con-
dition is that the relay immediately disengages af-
ter closing, and the power cord must be unplugged
and plugged back in for the relay to reengage.
Beware! The relay may disengage so quickly af-
ter closing, a person may only hear one "click" and
not realize the relay disengaged. To determine if
the relay is engaged, check the voltage drop across
the relay solenoid. An 11V drop across it engages
the relay.
Because Z801 is supplied by the stand by 5V,
the TV must be unplugged to reset shutdown.
5V
12V
drop
Relay Drives
bypasses the microprocessor
5V TV ON
to turn OFF the relay drivers.
0V TV OFF
+125V
Figure 1.
16
Microprocessor
(QA01)
15
Shutdown Curcuit
(Z801)
16
The shutdown circuit
for main power