TOSHIBA Technical Support Guide 2004-1
Rev-1
Shutdown Troubleshooting Guide
2004 HDTV Projection Models
Protective shutdown in these models will be indicated by the power relay disengaging and the
red power LED blinking at a half second rate. The power cord must then be unplugged and
plugged back in to restore operation. The purpose of this guide is to help narrow the cause of
the shutdown to a single section or circuit. Refer to the correct service manual for additional
information.
The voltage test points indicated in this guide should be measured with a peak-response
meter or an oscilloscope set to DC input. If a peak-response (or min-max meter) is used, set
the sampling time to one millisecond. A higher sampling time could cause errors. Do not use
a normal digital meter because the sampling time will be too long. Since you are attempting
to measure the peak voltage just at the point of shutdown, a normal digital meter might not
give correct readings.
Section One: X-ray protection. The high voltage is sampled at the reference pin of the CR
block, Z450 (at the white wire). This voltage passes through the blue CRT board and is
applied to pin 4 of connector P404 on the DEF/POW board. From there it goes to pin 10 of
Q306 and exits at pin 8. Q306 is a quad op amp that is used for current buffering. The
sampled voltage is then applied to the emitter of Q408 and on to Q409. If the voltage at the
emitter of Q408 exceeds the reference voltage across D490, Q408 and Q409 will be turned
on. This will cause the circuit of Q471, Q472 and Q473 to latch the set into shutdown.
For X-ray shutdown suspect the following components: T461, Z450, C440, C443, C444,
deflection yokes and other components in the horizontal output section.
Section Two: Over-current shutdown. Transistor Q470 and resistor R470 are part of the
over-current sensing circuit for the horizontal output section. The current for the horizontal
output transistor passes through R470. The base to emitter junction of Q470 monitors the
voltage drop across R470. If the current draw of the horizontal output circuit increases, the
voltage drop across R470 will increase. Shutdown will occur when this voltage drop exceeds
1.5 volts. (This voltage is very difficult to measure reliably. Since the voltage is measured
across the resistor and neither side of the meter is at ground potential, voltages induced into
the meter leads affect the measurement).
Measure the voltage at resistor R474 on the power/deflection board. Take this measurement
on the end of the resistor toward the rear of the set. If this voltage exceeds 13.2 volts at the
point of shutdown, then the set is going into over-current shutdown.
For over-current shutdown, suspect components in the horizontal deflection area such as:
Q404, D461, T461, C440, C443, C444, etc.
? 2004 Toshiba America Consumer products, L.L.C.
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