From whatever I have read about this model, it is similar to the MX500, but lacks the
sleep timer function (and probably the tip sense circuitry), so you should be able to use the MX500 schematic.
This one uses L4960 (40V max) vs the LM2576 in the MX500.
Apparently , Q1, Q2, Q4, C3 and C6, R2, R8, R9, R10 are possible failure points.