"electroninja" writes:
Ref your questions Sam:
Q. Not sure what your saying here about the fan?
A. Fan looks like an AC vs DC fan--one open air coil around
core--armature alum--motor has appearance of bathroom vent fan. Fan
runs on low speed only on first cycle but speeds up prior to shutdown.
Todays test shows 115 volts across motor's coil at both low and high
speed. Shaft rotates freely, but will try a drop or two of oil.
Q. Is there a thermistor to monitor magnetron temp?
Is there a schematic?
A. Limited schematic (unit door closed/cook cycle off)
One thermal switch on magnetron in series with power fuse--activation
shutsdown all power (not our case.)
- One oven thermistor shown as input to control unit circuit. No
details given (including wire color coding). Had thought this might be
convection oven temperature control.
- Control unit connected to a "relay unit" --Triac, small transformer,
relays etc. Schematic shows one relay that if activated would shutdown
magnetron and fan while leaving power to rest of unit (our case
possibly.)
--Action plan:
- Oil fan motor monitor affect
- Locate thermistor and test--assume a two wire device whose resistance
rises with temp. Uncertain what I should expect for ohm delta--comments
appreciated
There have been cases where for whatever reason, RFI from the magnetron,
triac, who knows, gets into the controller and does strange things.
Unfortunately, hard to track down those sorts of problems.
But you said it happens on Defrost but takes longer. Defrost is 10 or 20
percent duty cycle (I'm assuming this is your basic HV transformer/cap/diode
design) so any heating would be minimal.
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