Epson HX-20 problem

Does anybody know how to fix the classic protable Epson HX-20? This is my part of collections, I know it's work fine before. When I tried to switch on the machine last week, (it was after 15 hrs charged), the LCD didn't show up and there was no response on the contrast wheel. But I still tried to key in something, like "SOUND 10,10" and "LPRINT A", there was a beep sound and the text printed from the mini-printer. Then I plug in the AC adapter again and tried to switch 'on and off' many times on the startup switcher, the LCD worked again. At that time I thought the problem is solved. After one day later, the problem happened again, I needed to switch on and off many times to make the machine wake up. I am sure the machine is work on the first switch, because the computer responded my key strokes but the LCD still sleep. Really want to know what's happened on this machine and how to check/fix it? Thanks Man