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Symptom#1 : no boot, only a solid black screen.Hardware use a custom 68000 CPU marked "59" whose pinout is unknown.Found a 4.7uF 50V capacitor with anode terminal desoldered from its pad.This capacitor was part of the RESET circuitry along with a voltage monitor transistor (silkscreening suggests a PST518A IC but a generic BC547 transistor was used instead in order to detect a voltage and generate a RESET signal)

Fix#1 : replaced 4.7uF 50V capacitor @C43

Symptom#2 : board now boots but screen is all red.A dominant red color means that blue and green ones were missing.Traced them back to three transistors.Manifacturer/assembler used three compatible BC547 compared to original silkscreened part adapting their different pinout by rotating them and twisting the base and collector legs.This caused a short circuit between the base and collector of the blue and green transistors @TR2 and TR3

Fix#2 : Cleared short between blue and green BC547 transistors @TR2 and TR3.