regular regulator failure modes

[duck_arse]

I have a test circuit built using a SOT-223 package 3 terminal 5V regulator to power a 7556 circuit. circuit is shown here, for those interested:
https://i.imgur.com/xk4LrqH.png
IC2 is MIC5209-5.0BS [standing on header pins as temporary replacement for 78L05, known genuine parts from reliable source], datasheet here:
http://pdf.datasheetcatalog.com/datasheets/105/187404_DS.pdf

the circuit works, does all as expected, except it's outputting 9V squarewaves. so I've checked and tested and measured - there is 9V on the regulator in pin and 9V on the out pin, 0V on the ground pin. resistance measures between pins and pads is as expected, shows "no" conductivity between in and out, either probe polarity, while powered down.

so, my question, before I hack what I think is the offending part from the board (layout shown here, only for the brave: https://i.imgur.com/Jk2hhIL.png ), can anyone advise - is this *suppy out pin V equals supply in pin V* a common/expectable/known failure mode for three terminal regs? I've used this part on pins in builds before w/ no probs, but can see no other possible culprit.

advise? comments? abuse? experiences?

[R.G.]

I don't have any special insight into this particular part, so no help there. But I do know that LDO regulators have oddities about exactly how much capacitance is on their output. You might get the datasheet on the Micrel part (in fact, you probably already have it) and look carefully for hints about oscillation under capacitive loading, or recommendations about critical cap loading values.

[anotherjim]

I've managed all this time without going that near to any LDO reg's. They have a reputation for being awkward. The Datasheet shows especially for the BS types you want 0.1uF (fast ceramic?) input to ground right next to the pins and 22uF on the output.
Other than that, if I had 3 term reg apparently passing the input as is, I'd suspect the ground connection wasn't there. Internals drawing suggests you should be able to measure some resistance between ground and the output pin.

[amptramp]

The 555-type timers can pull several hundred milliamps during the change of output state.  It doesn't persist, but it is enough to upset some circuits.

[duck_arse]

[well, that was fun. no, wait, the other one ...... my screen said "no signal" mid session, so I had to kill that machine and 'up' a laptop with a new install on .... so I'll repost this post.]

thanks for answers. I wasn't using the LDO-edness of the regs, it's just they was smd and on special. after much poking today, I couldn't get the reg to regulate, so set about cutting it from the pins it was standing on. and the first one went -- PWwingg -- across the room, along with a corner of epoxy, so no post-mortem on that part.

but the new part went in, as seen in the bodge pic, and works as expected. plus, I might have found a use for the pads on the end of the perfs.



any parties interested in the circuit in question can see things in this bukket, like the test panel and some waveforms on the cro. a lucky few punters might be getting links to some sound/video samples shortly [you know who you are].

https://imgur.com/a/N3QdlLn

[vigilante397]

I'm a bit late, so congrats on getting it sorted, but as one that has burned up plenty of regulators in my time, I can verify that Vout = Vin is a pretty common failure mode for them. Most notably when I had a 78L05 go bad in a reverb build and sent 9V into the supply pin of my Belton brick, turning it into a literal brick