Viperdoc wrote:
First flight after annual, and the alternator light comes on over Lake
Michigan in IMC- left alternator belt thrown, which was replaced at the
annual. Never had any problems with electrics prior to this.

Replace belt, light comes on with application of power or electrical load.

Returned to mechanic- says it could be stuck counterweights on crank shaft
causing vibration that throws belts. I ask- why did this just start after
the annual, with no indication of problems prior to this?

Replace with another new belt- no change. Now note that no voltage is going
to alternator field. Diagnosis- bad voltage regulators (two), possibly bad
alternator.

Both voltage regulators removed and alternator as well. Repair shop says
they are all OK, but replaced brushes anyway.

Working diagnosis is now bad connection at alternator field wire, caused
alternator to run intermittently, and this is what threw belt initially.
Apparently, with intermittent loading of the alternator due to engine
vibrations, these pulsations caused belt to whip and jump off of pulleys.

My guess- wire was bent, kinked during initial belt change, starting cascade
of events.

Two questions: does all of this sound plausible?

Who is responsible for all of the labor, belts, and alternator and voltage
regulator check out?

Should the mechanic who changed the belt initially bear some of the
financial responsibility for this?


Yes, and it sound like it may be time to find a new mechanic.