most projo's have various protection circuits that will activate on a fault . (a service manual would be quite helpful)
a visual inspection is a good beginning . start with the pwr sup. look for domed /leaky 'lytic caps-replace as needed..
same applies to the deflection pcb . also look for burn marks and loose connections .
loss of vert deflection will trigger shutdown. look for poor connections on the vert output ic.
if the HV does come up , the h out xistor is likely ok. however, faulty tuning caps /flyback/HV Distribution block can all
cause shutdown .
convergence failures can cause depending on brand .
i'm not familiar with Mitsu projo's , thus can not give detailed tips.
i'll see if i can find a manual .........

good luck