On a NGC Tornado, oven would warm up fine, when cooking cycle is started, screen will either right away, or within 15 seconds, go blank and oven will continue to operate. Screen remains blank until oven is disconnected from power and then turned back on, then the screen is working fine and oven would operate as normal again, until cooking was started, and again it will go blank. I guessed I/O board but was wrong, new I/O board and right away oven is having same problem.
Anybody seen this? No mention of anything like this is in the service manual
Check that the ribbon cable and power cable to the vacuum florescent display are good.
This may help:
No Display (Blank)
Verify power 208 VAC or 240 VAC is going to the oven correctly.
If not, correct the voltage supply.
Control DOES NOT beep when any key on the keypad is pressed.
Check power going to the 24VDC power supply. Supply must have
or 240 VAC across L and N terminals.
If there is no voltage, replace F1 and F2 fuses.
If the voltage is OK, verify output of power supply is 24 VDC.
If there is no output, change the power supply. If the power
supply is 24 VDC, see below.
Output is 24VDC
Verify I/O control board has 24 VDC by checking the voltage on
diode (striped end) on the I/O control board to chassis.
Reference page 54
for a schematic of the I/O control board.
No voltage: Check wires from power supply to I/O control board.
Voltage is 24VDC, but 5VDC is not present on the I/O control
J3 connector: Replace I/O control board.
The control DOES beep when any Key on the Keypad is pressed.
Check all connections between the I/O control board and display.
loose connections. If connections are OK and 5 VDC is
present on the J3 connector, but there is still no display, replace display.
It sounds like with the added load of cooking the 24 volt DC supply drops below the needed VFD power. Verify the incoming line has no resistance and is the proper voltage. Like a bad/corroded power plug
The 24v supply does not drop during cooking and when this problem happens and it is right at 24v. The screen is on when cooking is started but within 30 sec display goes blank. Buttons still beep when pressed. Oven screen resumes operation once power is disabled and restored.