A very nice lady from Houston sent us the oven controller from her Whirlpool RBD275 built-in double oven. We rebuilt and returned ... then got it back a while later with a note saying the display is very dim. We powered it up on our test bench and the display looks great. After discussions w/nice lady the syptoms were: I can read the blue clock ok (but not great), I can't read the temp display after a few seconds of starting bake.
So, long story short ... wire nut connections on the main power feed to her oven are corroded ... a few seconds after you push "start" the bake relay kicks in and draws high current causing the control board voltage to droop.
On the bench we hooked up a Variac (variable transformer) to test at proper and then compare to drooped voltage. You can see in the pictures that at full voltage display looks great (lower) but with the line voltage dropped to 91V (upper) you can still read clock but the orange digits are almost gone. It's a characteristic of the display technology (vacuum flourescent display - VFD).
It's a good quick visual to see failing breakers and oxidized wire nuts (at least once they're degraded enough to add about 0.5 ohms of resistance to power feed).
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