I have a late version of the Osborne 1, it was clearly stored in a moist environment as many screws are corroded. When powered on, it beeps once and vertical bars are displayed across both the internal and external displays. Two alternating columns of characters fill the screen. Pressing reset seems to scramble which character fills the screen, and occasionally there are many characters, but always ordered in some way. These screen remains completely static until reset is pressed. Initially, after two or sometimes three presses of the reset button the floppy disk drives would rotate continuously and the beeper wouldn't stop. Now the beeper doesn't beep after the initial chirp, but in addition there is now more than one pattern of characters on the screen at once.
I have verified that all voltages are correct, and the RAM is receiving correct voltages as well. The RAM chips in bank D (closest to the front) are the warmest but nothing on the board gets hot enough for me to assume a short. Removing the double-density board doesn't seem to make a difference. Here are the pictures of the symptoms shown on the external display:
Additionally, when I remove the processor, the vertical bars and initial characters remain on the display, but the reset button no-longer has any effect on the system. Removing the character ROM eliminates all characters from the display, but doesn't change the bars going down the display as shown in the first picture. Removing the main ROM causes a continuous war-cry from the beeper. Keyboard input never has any effect on the symptoms. Pressing enter or tab at boot doesn't cause either disk drive to respond.
So, given all of that, I am inclined to suspect the processor or RAM, but I don't know where to start. I also figure the vertical bars and the failure to boot may be entirely separate issues. I read a comment by Tezza at the following URL:
http://www.vintage-computer.com/vcforum ... 13108.html
The piggyback test seems a good 'quick-and-dirty' method to diagnose some cases of bad RAM. While obviously not definitive, it did work with my Osborne.
Does my issue also seem like RAM? Would piggy-backing be a good place to start? I don't have any spare chips at this point. I am hoping anyone here can help me identify what my symptoms mean. I don't trust myself to de-solder multiple RAM chips without ruining solder pads and/or at least one chip, so I hope to do it as little as possible.