Scantronic 500r Front Door Tamper Won't Reset - Help Please

[Andy Beecham]

I've had a Scantronic 500r alarm for many years now and usually carry out replacement batteries in all sensors without an issue. However on removing the door sensor it triggered the tamper on the control panel and as I was struggling to realign the 3 metal prongs into the casing of the sensor, I decided to input the security code to stop the continuous beeping. After finally putting the door sensor front back on to the wall, I keyed in the security code and hit the reset button but it wouldn't reset and the front door tamper light flashes. Having turned off the electricity and removing the battery the system does seem to reset and the tamper lights disappear. However, when you try and re-arm the system it doesn't seem to recognise the door sensor although the system does arm. Clearly I'd like the door armed and so has anyone got any ideas as to what the problem is and how it can be rectified. Many thanks.