Scantronic 9800 system. Keypad 9825 not working

[LRCTech]

Hi. I have an old (circa 1992) Scantronic 9800 alarm system installed with the 9825 keypad. Its been working great for 'ever'. But after a recent mains power failure to the house, the display gave the 'Lb' indication for backup/auxillary battery low on the display. I disconnected the battery and mains power fuse. I have replaced the AUX/backup battery over the years 4 times before without any problems. I have fitted a new 12v lead acid battery today, but now the 7-segment display does not illuminate and the keypad appears to be malfunctioning. I enter 1234 followed by 07890 but all that lights up are the 2 yellow LEDs immediately under the top of the keypad, above the segment displays. The 2 x 7 segment displays, Power, Failure and Service LEDs do not illuminate. After several presses of the keys the sounder beeps for every key press and the yellow LEDs go out. I have checked the keypad is getting full 12v DC from the main panel . The onboard regulator (7805) is giving out 5volts to the 80C49HC controller and 74HC14N chip etc. The tamper switch on the back of the keypad PCB is working OK. I have looked at buying a used 9825 or 9827 keypad from eBay which are over priced. Would anyone happen to have a circuit daigram for the 9825 keypad? or any ideas, suggestions etc on what to check to get this working again. Thanks in advance for any help.

 

[sparkymarka]

Just replace it ….its not worth messing around with as it’s over 30 years old

 

[LRCTech]

Being of the generation that likes to fix things and give them an extended working life, would prefer if possible, to make it work that bit longer. I founded a Repair Cafe several years ago and todate have been successful in saving around 4 tonnes of household electrical/electronic devices going to the scrap heap, by repairing them rather than replace. Would be great to get the keypad working again.