Zenith Model SY3288DT 32" TV WILL NOT TURN ON

[Ron Novini]

Have a Zenith Model SY3288DT 32" TV that doesn't turn on.
This model has the familiar power supply and deflection board
setup on the right side and vertically mounted and shielded modules
(1 each of video, audio-if, pip, star, and micro) on the left
side board. If we allow the double ground pins of connector 3A6
represent pins 1 and 2, the standby power measurements at connector
3A6 on the power supply board would be as follows:
Pin 1 - Ground
Pin 2 - Ground
Pin 3 - 26.95 volts
Pin 4 - 39.87 volts
Pin 5 - 11.28 volts
Pin 6 - 0.00 volts
Pin 7 - 15.38 volts
Pin 8 - 13.71 volts
Please note that pin 6 on this connector seems to be the signal line
from the micro that turns on transistor QX3403 which causes current
flow in optoisolator ICX3405 on the cold side. This in turn would
cause current flow in the hot side of the optoisolator which should
enable drive output 2 on ICX3401 (pin 14). This drive output should
enable B+ production for the tv.
I have uncoupled pin 6 from the connector and measure for any change
in the line from the micro when the power button is pushed. There has
been no change in the line when this action is performed. It is obvious
to me that the micro is not turning on the set when the power button
is pushed.
These further measurements might be helpful.
Optoisolator ICX3405
Cold side Pin 1 - 15.44 volts
Cold side Pin 2 - 14.84 volts
Hot side Pin 3 (connected to pin 14 ICX3401 Drive Output 2 Enable)-0.24
volts
Hot side Pin 4 (connected to pin 15 ICX3401 -Vref) - 4.92 volts.

ICX3401 (MC34065P) Dual Channel Current Mode Controller/Totem Pole
Outputs
Standby Measurements
Pin 1 (Sync Input) - 0.00 volts
Pin 2 (Ct) - 2.46 volts
Pin 3 (Rt) - 2.46 volts
Pin 4 (Voltage Feedback 1) - 2.46 volts
Pin 5 (Compensation 1) - 2.94 volts
Pin 6 (Current Sense 1) - 0.08 volts
Pin 7 (Drive Output 1) - 2.67 volts
Pin 8 Ground - 0.00 volts
Pin 9 Drive Ground - 0.00 volts
Pin 10 (Drive Output 2) - 0.00 volts
Pin 11 (Current Sense 2) - 0.00 volts
Pin 12 (Compensation 2) - 6.63 volts
Pin 13 (Voltage Feedback 2) - 0.05 volts
Pin 14 (Drive Output 2 Enable) - 0.24 volts
Pin 15 (-Vref) - 4.92 volts
Pin 16 (Vcc) - 12.11 volts

Also both electrolytic caps on hot side of power supply check good.
Set will simply not turn on. Any help would be appreciated.
Thanks ahead, Ron


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[Andy Cuffe]

Ron Novini wrote:

Have a Zenith Model SY3288DT 32" TV that doesn't turn on.

I assume you have confirmed that the micro is getting +5v and that the
osc crystal is running? If the micro is getting power, then it's
probably a micro problem, not a power supply problem. In cases like
this I sometimes manually supply the turn on signal that should be
coming from the micro so I can see what's happening. I've also seen a
few TVs with a shorted, or leaky buttion that cuases it to ignore any
other button presses, including power.
--
Andy Cuffe
baltimora@psu.edu