Keys not responding (1-3,0,00) Sharp ER-3220

Our old ER-3220 suddenly stopped recognizing the 1,2,3,0,00 keys, no beeps just nothing. Everything else worked (more later), but can't get too far without those keys. I opened the case and saw the battery was starting to blossom so I ordered a replacement and welded it on. I also cleaned off the keyboard circuitry (plastic sheet with touch pads under the keys) as it was quite dusty and crumby, restaurant hands. So, turning the machine back on got nothing on REG MODE. After some research, my DIY SRV key brought it back to life but now none of the keys respond except CL, RECEIPT and JOURNAL. Am I missing a critical step to reviving it or is it time to get a new till? This machine was made in 1991 and working until 3 days ago! TIA for your suggestions and help!