[geeks] Voltage regulators don't!

[der Mouse]

> Grrr.  Rant alert.  [...7805s not regulating...]

Okay, this gets weirder and weirder.

Prompted by an off-list email, I redid the tests, this time being
careful to clip the voltmeter connections onto the device separately
from all other connections, to make annul contact resistance issues.
It still didn't work.  Except, as I picked the device up to disconjnect
it, it suddenly stabilized.  Pressing on the leads in various
directions made me suspect mechanical stress was responsible.

So I soldered wires onto one of them.  Same behaviour: worked under no
load; under load, collapsed to low output voltage until I picked it up.
A bit more experimentation indicated that it was *electrical* contact
between my fingers and the leads that was responsible (pressing with
insulating plastic in place did nothing).

So I connected a resistor between ground and power *input* (3.9K, that
being what I had handy, even though it's far less than dry skin contact
resistance - and my skin was basically dry).  This seemed to stabilize
it.  So I started to set things up again, and had more trouble.

Now I've got a 7805 connected up to power, 150 ohm load, the Fluke
voltmeter on the output, and a 3.8K resistor between the _input_ and
ground.  Sitting there, the voltmeter shows about 1V.  But if I touch
the input side of the 3.8K resistor, the voltmeter immediately
stabilizes on 4.98V!  I've checked, several times, that I'm not
electrically connected to anything else.

Next up, I'll try adding some ceramic disc caps here and there - even
if I'm not dc connected to anything, body capacitance is still present.
The environment is probably rather electrically noisy, but I have
trouble seeing how picking up additional noise onto the power input
could *stabilize* the 7805, so I'm currently guessing it's stray
capacitance that's responsible.  (I tried switching out the 30000uF
filter cap for a 470uF cap, in case there was some funky resonance
going on; no difference.)

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