Its most likely a lose wire, or potentially faulty PCB. There are no fuses protecting the control board\display, just the high energy parts such as elements and the magnatron.
Your best bet is to call our an appliance engineer who can remove it, fault find and give you a quote for repair, and in most cases if it needs a part they will take it away for you, repair it then drop it back off and reinstall it for you.
If you would like me to recomend someone in your area can you provide me with your postcode.
I would suggest you give Dalhouse a call on 0121(###) ###-#### they will come to your property free of charge and give you a estimate for repair.
Based on the age of the appliance I think you might be correct in that its uneconomical to repair, but certainly worth getting them to quote for repair, as it may be something simple, or failing that they can at least recommend a replacement and install it for you.
Please let me know if I can be of any further assistance.
I havent heard back from you please let me know if you have any follow on questions.
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