2PSU, Same problem-same fix-different results: Odd Power supply output "flicker"

[EEVPiobee]

Hello there!

Today I fixed two small power supplies, same model, same design, same batch on manufacture production run... (SMPS, 12v, 4a, rated, classic Chinese design) that broke down two years ago (don't say I'm slacker, I just reallly busy and those were not a priority at the moment)

The problems on these two turned out to be the PMIC that went bad for some reason and the output diodes (2x 3amps in parallel argh!) were heating up, even without load on them...

So here is what I've done...

I changed:
PMIC for new ones, same model (and added a socket for serviceability) (CR6853T)
output diodes (cheap generic) for a Schottky TO220 pack 10 amps (B10150CTG)
and
Changed the opto-couplers used for feedback for new ones if ever this was the reason PMIC didn't work properly. (PC817C)


This trick WORKED on both, (at least nothing blows up, and now passes the finger test) but...

One of the two power supplies gives me a "flicker" on the output voltage... I'd say it's some sort of a sawtooth every 0.3-0.5 seconds or so...

for that purpose, let's call them PSU1 and PSU2...

As PSU1 outputs a perfect steady 11.89volts (good enough to me for a 12v supply and what is powers)

PSU2 Reads from 11.86 and drops down to 11.6 within a .3-.5 period delay and then instantly raises back to 11.86v (the led on the board flickers as well)

Any ideas?? 

p.s. I haven't tested them with load on them yet, also, I tried swapping the new PMICs between the two but same result... Flicker stayed on PSU2