Zenith R50V26 Service Manual

Also see for R50V26: Operating guide

Contents

Zenith R50V26 Service Manual Manual pdf 27 page image

CIRCUIT DESCRIPTIONSPV154 - 923-03506 3-3 ZP26/28 - SERVICINGHOT GROUND SIDE SHUT DOWN SENSING CIRCUITS(INTERNAL TO IP01)LATCHED SHUT DOWN MONITORS(AC must be removed to recover)1. Pin 4 is monitored for Over Voltage internal toIP01.2. IP01 itself is monitored for Excessive Heat. Thisblock is labeled T.P.O. (Thermal Protection Over-load).RECOVERING SHUT DOWN INPUT(Driver IC will recover on it’s own when trouble isremoved)3. Pin 5 besides being used as a regulation input, italso monitors low ohm resistors RP10, RP11, RP12,and RP16, (All are 0.22 ohm resistors). If theseresistors have an excessive current conditioncaused by monitoring the current through the in-ternal Switch MOS FET, the voltage will rise. Pin 5has an internal Over Voltage detection op-amp. Ifthis voltage rises enough to trigger this op-amp,the IC will stop producing a drive signal.COLD GROUND SIDE SHUT DOWN CIRCUITSThese Circuits are broken down into the appropriatecategories as described earlier.VOLTAGE LOSS DETECTION1. Shorted 220V (DP24 and DP25) Inverted by QP03then through DP282. Shorted SW+35V (DP26) Inverted by QP03 thenthrough DP283. Shorted 28V (DP27) Inverted by QP03 thenthrough DP284. Shorted Deflection Transformer or Miss-operation(D707 and Q705) then through D705NEGATIVE VOLTAGE LOSS DETECTION5. -28V Loss Detection (RP21, RP20, DP35, DP21 andDP22)EXCESSIVE CURRENT DETECTION6. 115V Deflection Power Supply (RP24, QP02, DP18,DP19 and DP20)7. 28V Vertical IC I601 Power Supply (R629, Q609,D608, and DP31)VOLTAGE TOO HIGH DETECTION8. Excessive High Voltage Detection (DH17, DH13 andDH15). Sensed from the 50P Voltage generatedfrom pin (5) of the Flyback Transformer TH01. Also,(DH14) sends a high command to the HorizontalDriver IC IH01 pin 7, to defeat Horizontal DriveOutput if this voltage goes too high.9. Side Pincushion failure generating a High. (D702,and D703).10. Deflection B+ Too High. (DP17, RP26 and RP27).11. SW +9V Voltage Too High Detection. (DP29 andDP30)12. ABL Voltage Too High Detection. (DH15)If any one of these circuits are activated, the powersupply will STOP, and create a Power Supply Shut downCondition.SHUT DOWN CIRCUIT DESCRIPTIONSShut down occurs when pin (1) of Connector PQD2 calledPROTECT goes High. This High is routed to the Sub PowerSupply PWB and is impressed on the base of the RelayDriver Transistor Q916 turning it On. When Q916 turnsOn, it removes the Power On High and the Relay S901will disengage and removes the AC source from the De-flection Power Supply.Please use the Commonly Used Shut down Detection Cir-cuits for the description of how the circuit works.VOLTAGE LOSS DETECTION1. Shorted 220V (DP24 and DP25) Inverted by QP03then through DP28. The cathode of DP24 is con-nected directly to the 220V line. If it shorts, thiscircuit is activated and pulls the base of QP03low. This output High is routed through DP28 topin (1) of Connector PQD2 called PROTECT and ShutDown occurs as described above.2. Shorted SW+35V (DP27) Inverted by QP03 thenthrough DP28. The cathode of DP27 is connecteddirectly to the SW+35V line. If it shorts, this cir-cuit is activated and pulls the base of QP03 low.This output High is routed through DP28 to pin(1) of Connector PQD2 called PROTECT and ShutDown occurs as described above.3. Shorted 28V (DP27) Inverted by QP03 thenthrough DP2. The cathode of DP27 is connecteddirectly to the 28V line. If it shorts, this circuit isactivated and pulls the base of QP03 low. Thisoutput High is routed through DP28 to pin (1) ofConnector PQD2 called PROTECT and Shut Downoccurs as described above.4. Shorted Deflection Transformer or (D707 and Q705)or D705. The Deflection circuit generates the ac-tual Drive signal used in the High Voltage sec-tion. If a problem occurs in this circuit, the CRTscould be damaged or burnt. D707 is connected toR728 which normally passes the same pulse as usedfor generation of the H. Blanking signal. This pulseis generated off the Deflection Transformer T752.The pulse is rectified by D707. This rectified volt-age is normally sent to the base of Q705 keepingit On and its collector Low. If the Deflection cir-cuit fails to produce the pulses for rectification,the base voltage of Q705 disappears and the tran-