Vsc: Scan Voltage
The Vsc Scan Voltage is generated at the Y Board Assembly and is produced after the Y Board receives the Vs Supply
Voltage from the SMPS (Switching Mode Power Supply Board). It is approximately -190 Volts (-190V in the example la-
bel) and is combined with the Scan Signal from the Logic Board by the FETs on the Y Board.
The Scan driving signal is then fed to the Scan ICs located on the Y Buffer Board(s) of the panel and is responsible for
scanning left to right, across the screen, and top to bottom, in a Progressive Scan, that is, one horizontal line at a time.
Repair Scenario 1
Symptom: The panel will not turn on. The TV shuts down after a 3 second interval.
Troubleshooting: Measuring the ―Vital Signs‖ shows Vs is OK, but there is no Vsc Voltage or a rise in voltage.
Repair: Replace the defective Y Board. Also replace the Y-Buffer Board(s) since the Scan ICs may also have been af-
fected.
Note: A visual inspection of the Scan ICs on the Y Buffer Boards (Scan Board(s)) is important and necessary. Physical
damage to any of the Scan ICs can be a quick confirmation of failure. Failures, however, can occur without any physical
problems being observed. If any of the ICs fail, replace all Y Buffer Boards (usually 1 or 2 assemblies) and the Y-Board.
Repair Scenario 2
Symptom: The panel will not turn on. The TV shuts down after a 3 second interval.
Troubleshooting: Measuring the ―Vital Signs‖ reveals no Vsc and no Vs.
Repair: Since Vsc relies on the Vs feed from the Power Supply, first troubleshoot the no Vs condition. To begin, test Vs
for a short to the chassis ground. The short can come from the Y-Board or X-Board. Remove the Power Supply Vs feed
to determine which board has the short. Replace the defective Y or X Board. If no short exists, test the power supply with
the connectors removed.
Note: Also verify the Logic Board is sending an active high signal to the SMPS to turn on Vs.
Ve: Erase Voltage
The Ve Erase Voltage is generated at the X Board and is derived from the Vs voltage from the Power Supply. The Ve
voltage, approximately 100 volts, (95V on the example label) is primarily used to assist the Y in erasing previously acti-
vated cells and neutralizing the erasure before the next scan.
Repair Scenario 1
Symptom: The TV turns on, but the video has continuous image ghosting or retention from previous frames.
Troubleshooting: Measuring the ―Vital Signs‖ reveals no Ve.
Repair: Replace the defective X-Board.
Page 14
Volume 4, Issue 11 Consumer Electronics Newsletter Samsung Tech Talk
Plasma TV Repair Made Simple, Part 2
continued
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