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14

MM/MMC/DTV Troubleshooting Guide

Temporarily unsolder JW902, if set operates check XRP circuits & +12V Sense Line (see NOTE below)

B

A
HV Sample (from T700-7) XRP JW902 H_Pulse_B from T451-14
(Horz Flyback Pulse)

+12V Sense
Active Lo

Remove Deflection SIP CBA & short B-E of Q24105. Reinstall CBA. If set runs, check Horz Drv & Horz Output. If set doesn't run, unsolder pin 18 of J14102. If set runs after unsoldering pin 18, suspect Q24105. If set still doesn't run go to next step. +12Vr R844 Scan Loss (1) Q24105 5 3 Scan Loss SysCon Micro U13101 R13130 Scan Loss (2) Fan Detect Q813 14 Pwr Fail

CR902 CR24100

Q24103 Switch

Horz Scan Loss Detect Normal = Horz WF

+8Vr

H Drive V Drive

1 Lo Level 20 Horz/Vert 10/11 Gen U350 CR803 51V CR805 36V

C

2H Scan B+ Gen Q800 Scan_H_A from T451-8
(Horz Flyback Pulse)

Short B-E, if set operates check 2H Scan B+ Gen circuits or Horz over drive. If set doesn't run, check Q813. CR807
NOTE: All components & TP's are 14000 series unless otherwise indicated.

(2.X Horz Over Drive Detect)

Scan Loss Block Digram
NOTE: Servicers who defeat safety features or fail to perform safety checks may be liable for any resulting damages and may expose themselves and others to possible injury.

Scan Loss Detect Overview
The Scan Loss detect circuit monitors not only horizontal scan loss but also XRP, +12V Sense, horizontal drive level (overdrive), Scan B+ overvoltage and loss of horizontal drive. Horizontal scan is monitored at the anode of CR24100. If horizontal scan is lost, the base of Q24103 is pulled low turning it on. This turns on Q24105, pulling the Scan Loss input (pin 3) of the System Control micro low and shutting down the set (pulsing shutdown). The XRP and +12V Sense circuit, when activated, pulls the anode of CR24100 low via CR902 and causes scan loss shutdown. Scan B+ is monitored for overvoltage by CR803 (51V zener). If Scan B+ rises too high, CR803 breaks over and turns on Q813, which pulls pin 3 of the System Control micro low shutting down the instrument. Horizontal overdrive is detected by a pulse from T451-8 and is applied to CR807 which acts as a rectifier. If the DC voltage on the cathode of CR807 rises above 36 volts, CR805 (zener) breaks over and again Q813 turns on pulling pin 3 low. Two (2) other shutdown inputs to the system control are the Power Fail input at pin 5 and the Fan Detect input at pin 14 of U13101 (System Control Micro). The Power Fail and Fan Detect inputs also cause a pulsing shutdown when activated.