Still haven't gotten my hands on a laser thermometer (but I do have a source). Here's what I found that hopefully will help someone.
1. Convection Fan Blade wasn't loose, bearing is bad. New bearing, mounting plate, holder plate, pulley and belt are on order. Insides of this thing haven't changed in 18 years, except that bearing assembly has a new version. I used an R-930AK service manual you can get here
2. Found a burned wire end and a loose connector at the heating element neutral side. Cut the wire back, added a new heat-resistant lead and cleaned the element connection.
3. Found a burned wire end at the primary interlock switch common terminal. Cut it back, added a new crimp connector, and cleaned the switch terminals.
4. Found loose connectors and carbon on the common terminals of every switch. Cleaned the terminals and pinched the connectors for a snug fit.
5. Due to loose connectors and carbon buildup on the damper switch common terminal, the damper was not closing consistently in convection mode, allowing heat to escape from the oven cavity into the outer casing. Cleaned the terminals and pinched the connectors for a snug fit. The damper now works as expected and food is cooking in convection mode within the expected amount of time.
6. Thermistor reads almost nothing using both a digital and analogue multi-meter. Service manual says it should be Approx. 350kΩ - 155KΩ @ a room temp of 68˚F(20˚C) - 86˚F(30˚C). So it should be replaced, but Sharp wants $45 for that thermistor. The oven works, registers temperature and cooks food at the set temperature in the expected amount of time. Thermal cut-off isn't kicking in because the service manual says that would shut down the entire oven. So I'm personally going to hold off on that until I get my hands on the laser thermometer to see how far off it is.
- DurhamAppliance likes this