After 25 years of trouble-free use with _no_ changes at all, I am suddenly
having problems with a 115 volt grounded branch circuit. The circuit is
connected to a 30 amp breaker and feeds three duplex grounded outlets and a
fan/vent hood over the stove in my kitchen. The branch feeds from the breaker
into one of the three outlets ("outlet #1") and splits from there to feed the
other outlets and the vent hood. I have a microwave (Amana Radar-Range, 20 yrs
old) in one outlet ("outlet #2") and nothing plugged into the other outlets.
Recently, if I hit the Start button on the microwave, it dies, along with the
vent hood. The really weird thing is that if I plug an ordinary work light
with a 40-watt bulb into "outlet #3", the work light works, _and_ the
microwave and vent hood start working again, at least for a while. When the
problem occurs, a voltmeter shows 115 volts in outlet #3, but minimal voltage
(maybe 50 volts) in outlet #2. (I cannot remember right now what the voltage
in outlet #1 is, but I think it sometimes shows normal and sometimes not.)

Here's what I've done to troubleshoot the problem:
1. Verified that the microwave works okay when plugged into a different branch
circuit (in fact, I can sometimes also get the problem to occur with the
microwave unplugged, just by plugging the work light into outlet #2, so the
problem is not related to the microwave.)
2. Cycled the circuit breaker, pulled power and verified the breaker terminal
is securely screwed down, and, finally, switched the breaker with another
identical one in the panel.
3. Disconnected all wires from all outlets and ran continuity tests on all
parts of the circuit with an ohmmeter. Continuity was good on all wires.
None of the above solved the problem, so I did the following:
4. Removed and examined all outlets, looking/smelling for signs of burning or
scorching. None found.
5. Bought a new outlet and swapped it for outlet #2 (the one the microwave was
plugged into). Problem did not go away, so I
6. Swapped the old outlet removed from outlet #2 for the outlet in outlet #1
(the one that "feeds" the other outlets). Problem did not go away. Did not do
anything to outlet #3, since it always tests good.

As I said, this circuit has run without problems for 25 years. Also, there
have been _no_ wiring changes of any kind in the house for at least 10 years.
No fires, water damage, lightning strikes, etc.

The only thing I can think of to do now is to replace _all_ the outlets with
new ones. Does anyone else have any other suggestions?

Thanks in advance for any help.