These two components are the most likely ones to be at fault if your Atari isnt working.
AV Mod Kit for Pal/NTSC Atari 2600/7800 6 switch 4 switch and Junior Consoles
NEC CoreGrafx Capacitors / 20 x Capacitor Kit + Jailbar Fix + Voltage Regulator
6-wire Voltage Regulator For Kubota, Kokusan Denki, Perkins and Yanmar Dynamos.
BestParts Voltage Regulator Thermal Module Replacement for Dell Alienwar Aurora R11 R12 N1C1D VRM HeatSink
Super Nintendo SNES / 10 x Capacitors + Voltage Regulator Kit / SNSP-CPU-01/02
LONCIN Voltage Regulator 1P91F, 1P96F