Not trying to defend the shady parts, but I assume you've checked the capacitance and/or ESR of the bulk cap(s) upstream of the regulator? If there's more (good) capacitance downstream than upstream, and no reverse-bias protection diode is present, that could explain both the original regulator failure and the new ones. They could be taking some damage at power-off time that curtails their operating life drastically...
All of these questions have been covered many times in this thread now, but given that it got unnecessarily derailed for a couple pages I'll recap again to save you sifting through:
- The original regulator failed due to the owner of the unit poking around inside and apparently shorting something out. These new EVVO regulators failed but the newer ones of a different brand have worked just fine
- All power supply components had already been tested and confirmed working. Protection diodes ARE present
- These regulators not only failed while powering the unit, but also when the power supply was only driving a DC load which rules out all other circuitry in the unit
- They didn't even last long enough to be powered down once so definitely couldn't have copped that kind of damage. The first one failed at power up, and it was confirmed on the other two that any load exceeding about 1A would kill them instantly (the actual load is something like 1.2A from memory so it makes sense why the first one died while powering on the unit). On that note, I can't remember if I mentioned it originally but just to state the obvious, the supply WAS checked and working before connecting to the unit, just not heavily load tested as I had no reason to think these couldn't provide the rated current and I'd already confirmed the rest of the unit powered up OK with a bench supply