Hi Guys, I'm trying to fix a dead Model 100 which gives a blank screen when powered on. The machine is not responsive to keyboard input as well. I can't get it to beep. While poking around with the oscilloscope it seems the power is ok. The clock input to the CPU is also probably good enough. The only chip that gives me a messy signal is the 81C55, which routes all of the I/O from the keyboard and LCD screen. I've tried reflowing all the connections to the chip. There was a moment when the thing beeped as I pressed a bunch of keys and the screen was giving me garbled output, but upon hitting the reset button everything died again.
I'm thinking I need to replace the 81C55 but wanted a second opinion. What do you guys suggest is a good replacement if I do need to buy one? Here is a lonk to my oscilloscope output: http://jovan.freeshell.org/weblog/ Thanks, Jovan
