TI-99/4A rolling white bars and a low pitch humming on power up

[EPOHouston]

I know the external power supply is good, and I know the RF modulator is in good shape. The unit was in bad shape, so I wouldn't be shocked if there's multiple faults here... I don't know much about fixing the TI 99, so I was wondering if someone could help me diagnose it. Thanks!!

 

[Chuck(G)]

Have you measured the ripple voltage on the PSU output?

 

[EPOHouston]

I actually haven't yet, I'll check that when I get the chance and report back. Thanks!

 

[Ksarul]

Note: the external power supply just steps the AC voltage down to something the console's internal power supply can handle to create the DC voltages the console needs (+5, -5, and +12 volts). The internal supply is under the cartridge slot.