I had the same SX-1050 "overheating surge resistor" issue recently. The solution was:
1) Repair blown LChan outputs
2) Rebuild
Power Supply Assembly-A (AWR-103)
3) Rebuild
Power Supply Assembly-B (AWR-104)
4) Replace C1 (10uF 63v) on AWX-098
When they outputs are blown, the short prevents C9, C10 (470uF 80v) on
AWR-104 from developing the needed 76VDC on Pin6 which is then dropped to 48V via R2 on AWX-098 to power S2 SoftStart Relay. If original i.e. 40-yrs-old, C9, C10 are trash and won't hold a charge anyway. Even if the 72V on Pin6 is OK, if C1 on AWX-098 softstart assy is old and maybe shorted and won't hold a charge, S2 still won't close. Since S2 won't close within 500mS at turn-on, the continuous surge current is continuously routed through R1 (3.3ohms 20W) and the 10A TCO (microtemp). If left to continue, heat from burning R1 will open the TCO forcing primary voltage shutoff. Fortunately on mine, I shut it off immediately after starting to see the overheated R1 burn the masking tape that thermally-couples the TCO close to R1. That saved me from having to install a replacement TCO. Everything became normal after rebuilding the above-mentioned assys. Scary when it first happened!