Friend check this article ... OCP CIRCUIT, OVER CURRENT PROTECTION, OPERATING THEORY The +135 vcc line supplied from The main Power Supply is monitored by the OCP circuit consisting of Q590, R591 and associated elements. The current flow of the +135 vdc line flows to the emitter of Q590 through a voltage divider circuit consisting of resistors R594 and R595 . If the current increases in the +135 vdc line, there will be a voltage drop in the resistance R591 . When the current is large enough that in R591 there is a voltage drop of approximately 1.2 vcc , Q590 will switch from cut-to-conduction mode, at which point the current flow in the voltage divider conformed by R594 and R595. Once the voltage drop across R592 reaches a level of 1.2 volts, it will drive into D562 . By cathode, D562 will supply a voltage of 0.6 vdc which will be applied to the base of Q572 . The circuit called Latch , consisting of Q572 and Q573 , works as follows: The voltage of 0.6 vdc from D562, induces Q572 to receive direct polarization and therefore it changes its cut-off state to conduction. Upon entering the driving mode, Q572 sends the base of Q573 to Earth causing the latter to also change its cut-off state to conduction. So far, it is necessary to pause to clarify that the circuit Latch will remain in such a state, the conduction, as long as the receiver is not disconnected and returned to be connected to the AC network The activation of the Latch circuit will cause the voltage directed towards the base of the transistors Q006 and Q608 , reduce below its driving point, 0.6 volts , which will cause both devices to change their driving state to the cut-off state. Switching from on to off on Q006 account will cause R055 to send a high logical state to PIN 72 (I-HLDWN) of IC001. On the other hand, switching the state of conduction to cut will cause Q608 to eliminate the ground point of RY600. When deactivated, RY600 disconnects the main Regulation Source circuit and thus, the receiver is put into Standby mode. The high logic state applied in IC001 via PIN 72 (I-HLDWN) automatically activates Auto-diagnosis and the STANDBY / TIMER led, Flashes in sequences of two.