The Tek 577 curve tracer is more than 25 years and components start to fail from time to time. The symptom is front YELLOW light ON (Collector Supply Disable Light) after power on and cannot output any voltage. After tracing, the circuit, the reasons is due to K115 not turn on, due to K125 not turn on, due to Q588 open. Replace new 2N222A to Q588 but always burnt (try 3 pcs) after power up! Later check base voltage is at 6.xV dc which is too high relative to Emitter at -12V. Thus transistor will be burnt after power up. Check Q586 is fine and then after removing Q586, the base at Q588 is still very high voltage. Thus suspect C587 defective (leaking). So change C587 by using 0.68 + 0.47 = 1.15uF (original is 1uF) from Tant to film capacitor. Also change C586 as it may also be defect soon. After plug in Q586 and Q588, the set works again! Here are the pictures of repair.
Lesson Learnt: Tantalum capacitors when failed, it always leaking or even short circuit!
