It depends on a couple of things. Firstly, has the bulb that illuminates the cavity blown? If so, there is a good chance that part of the pcb track has blown, it can be easily mended by soldering in a link wire across the break (making sure to follow the line of the original track) alternatively, if the bulb has blown but the pcb track is intact, then the small relay that feeds the bulb, fan and turntable drive has possibly frozen or a dry joint on the pcb is not allowing the relay to close.
The other possibilities are mcu failure or fractured zener diodes, this particular board seems prone to one of the zeners being installed under more 'tension' than they can tolerate or maybe the zeners are particularly weak, but either way they have been found cracked and fried. Test the zeners with an ohm meter - the reading should be about 500 ohms reverse and 1500 or greater forward.
We process about 100 delonghi microwaves a week and this is a fairly common scenario.
If all else fails, e-mail chainstore_massacre@yahoo.com for spares, repairs or replacements.
Finally, BE WARNED !! There are very significant dangers involved when repairing microwaves, the magnetron needs around 4.5 - 5.0 kv to run and the secondary side of the main transformer produces roughly 2 kv step up assuming average mains input, couple this with the half wave doubler circuit using the diode/capacitor array you have a very, very high voltage which is stored in the capacitor even after the power is switched off (the bleed resistor takes a short while to discharge it, sometimes the bleed resistor is not working in which case it can take hours for the cap to discharge by itself)
As well as the potential for electric shock, microwave leakage can cause significant injury, make sure there are no gaps in the door closure and that the magnetron is secure to the chassis.
IF IN DOUBT, SEEK QUALIFIED HELP. ALWAYS PROCEED WITH EXTREME CAUTION.
Karl Mitchell
April 2007
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