Bad Primary Switch (B2)

Microwave Repair
,
1

Timer counting down but no fan and no power to
magnetron

Opened-up the unit, found signs of overheating on the
quick-disconnect to switch B2 (primary switch)

Removed the switch and found that the N.O. terminal
has overheated, plastic switch casing is slightly melted,
switch no longer operates correctly (N.O. on only when
partially activated, off when fully activated)

I am thinking there are two possibilities:

  1. quick-disconnect connection went bad over time, increasing
    resistance, causing overheating, eventually resulting in the
    damage I see

  2. overheating and damage are a symptom of a short-circuit
    or similar more serious issue

For (1), I can simply replace the switch and clean-up or
replace the quick-disconnect

I am more concerned about (2). How would I check for an
over-current or short-circuit?

MV

2

Measured the D.C. resistance of the low-voltage winding
of the H.V. Transformer and got 0.4 ohm. (This is with both
secondaries disconnected)

That doesn’t seem reasonable, does it?

MV