The machine power thick film blocks using 3 s0680rf. The CPU is KS88C8432-12, small signal processing using TDA8841 microcontroller. SLRservice manual download site
 SLRservice manual download site
Observe the power indicator light is not bright. Disconnect after class. + B 100 w bulbs, switch on the light bulb not bright, measured filter voltage is 315 v, for a long time can't discharge, judgment for the power supply without oscillation. Check with light coupling (2) feet in a connected component labeling for KA431, due to my limited knowledge, preliminary judgement for SCR. At this point measured KA431 R changes between 0 V ~ 1.5 V, K changes between 3.9 V ~ 4.3 V, welding measure is ok, peripheral components substitution also checked, fruit. SLRservice manual download site
 SLRservice manual download site
Then substitution KA431. KA431 called precision voltage reference chip, also known as the three end precision voltage components. When R voltage below 2.5 V, the chip output low level, interelectrode approximate open A, K, K voltage is not controlled by R voltage; If the voltage is greater than or equal to 2.5 V R, K voltage drop, when the chip is equivalent to a control sensitive low impedance power supply, its biggest power source for 150 ma.SLRservice manual download site