I purchased a 5V step-down voltage regulator (Part # 2177) many months ago and finally got around to using it to step down 12 V from a switching power supply. When I wired it to a 5V power input, the 12V supply would only make a single clicking sound and not come on. I wanted to confirm that it was putting out 5V and disconnected it from the board I was working with. When I turned the supply on I heard a popping sound and then the voltage regulator smoked. Resistance measured on the 5V end is 1 kOhm and 140 kOhm on the 12V end. Is there any reason that this would happen ? I suspect that the regulator was bad. Thanks.
More likely, you connected the regulator incorrectly, or the 5V load drew too much current for the regulator. However there is not enough information in your post to tell.
Please post a complete schematic diagram or clear photo of the entire circuit and describe the characteristics of the 12 V power supply and 5V load in more detail.
I think we also received a support email from you about this regulator. It sounds like when the BEC smoked, the printer was disconnected from the 12V 30A power supply and only the BEC was connected. Is that correct? Power supplies often produce transient voltages well above the nominal voltage on startup and it is possible that the BEC was damaged by such a transient voltage. If you post pictures like Jim suggests, we can look to see if there is anything else that might be an issue.