NEC FP1355 Service Manual

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Contents

NEC FP1355 Service Manual Manual pdf 13 page image

1 - 71.1.7 Degaussing circuit(1) The automatic and manual degaussing circuit is provided.The circuit prevents the picture from dropping its quality due to the magnetization on CRT,and operates as follows.(2) When powering ON, Q963 flows to activate RY901 by DG signal output by the MPU.This will make the current flow through the demagnetizing coil for demagnetization. Thedemagnetizing time is approximately 5 seconds.Manual demagnetization becomes possible by selecting the demagnetizing menu on theOSD picture.1.1.8 Power management circuitTurn ON the power management setting on the menu picture of OSD, and the energy savingmode shown in Table 2 will be ready depending on whether the horizontal/vertical sync. signalis present or not.1.1.9 Protective circuit(1) Overcurrent protective circuit (primary side)IC902 is provided with an overcurrent protective circuit. The voltage drop generated by thedrain current that flows into R928 is input to Pin 1 (OCP/FB terminal) of IC902. When thevoltage reaches 0.73V, the overcurrent protective circuit will be activated.(2) Overcurrent protective circuit (secondary side)To protect the parts on the secondary side, the short-circuit detection circuit is provided onthe secondary side output (+215V, +80V, +/-15V, +7.5V), one for each. As an example of+215V, the output line of +215V is monitored with R964, R965, D966 and Q961. If it dropsbeyond approx. +140V for any reason, Q961 will be turned ON to transmit the informationto the MPU. Then, since the MPU sets P-SUS signal at LOW, Q902 will be turned OFF tocut off the power to IC902 in order to stop IC902. (IC901 will be also stopped at the sametime.) The overcurrent protective circuit is designed to be activated when the output volt-age drops approx. 30 to 40%.(3) Overvoltage protective circuitR918, R919, R920 and R921 are used to detect the overvoltage in the higher harmoniccircuit, and the tertiary coil (Pin 9) of T901 is used to detect the overvoltage of the voltageon the secondary side. They are both connected to the overvoltage protective circuit(Q904, Q905) on the primary side. If any overvoltage results for any reason, Q905 will beturned ON to turn ON Q904. Then Q902 will be stopped. Since the power for IC901 andIC902 is cut off as Q902 is stopped, the switching operation will be stopped.OFFONOnOffOnOffOnOnOffOffActiveBlankBlankBlankPower Save VideoH-sync V-sync LED indicator140W3WPowerconsumption Recoverytime¥5 sec.GreenOrange