You have a fault in the controller module. I suspect a bad power supply capacitor is feeding dirty voltage to the control electronics.
Unplug the range, then open the control panel (usually you get into it from the back). Remove the control module (warning: handle it only by the edges to prevent damaging the circuitry with static electricity from your fingers). You may not have to disconnect everything at this point; you just need to see the component side. Look for any electrolytic capacitors that have a domed top instead of a flat top. Normal is flat top; domed capacitors are burned out. Also, if you see a smaller electrolytic capacitor that has obviously had its can enclosure pushed off the base, that would be bad. See the photo for a comparison of bad (marked with red boxes) vs. good capacitors.
These capacitors are relatively inexpensive to replace, usually less than $1.50 US from on-line sources. I recommend using the Panasonic FR series as the most reliable replacements. It should be much cheaper to pay a TV technician to put in the parts than to buy a replacement controller. Note: if this is what you find, and you want to take the module out for service, first go to a computer parts store and beg an anti-static bag from them. Make sure it's big enough to hold the controller including the keypad (keypad connectors can be tricky; if you don't know how the latch on the connector works you can damage the connector or keypad cable, so leave it attached and let your technician worry about it). I don't have the service info for your model, so I wouldn't know what kind of latch it uses without seeing it. Again, handling the module only by the circuit board edges or whatever mounting frame it is in, place it in the antistatic bag for transport. DO NOT USE AN ORDINARY PLASTIC BAG; these generate static charges instead of protecting from them.