This is my first post here on Stardot. A few weeks ago I picked up my first ever BBC computer from eBay. Since then I've been trying to get it working.
The machine is an issue 4 with no Econet or disk controller. The original fault was a continuous tone from the speaker and no image on the display.
I've been combing through posts on the forum and I've found a lot of helpful information that has gotten me this far. After much troubleshooting with a logic probe and Tricky's test rom, I've replaced:
IC 45 (74S139)
IC 24 (74LS138)
IC 14 (74LS245)
IC 39 (74LS283)
IC 66 (4816 RAM)
The computer will now boot, but there is no startup message, only a blinking cursor. Typing will advance the cursor but no characters are printed on screen. I can blindly enter the "Mode" command to change screen modes. In all screen modes except 7, text is printed correctly and I can execute Basic commands. If I switch back to Mode 7, no characters are displayed, only the cursor.
I can get a startup message to appear if I remove IC 3 (VIA):
Code: Select all
BBC Computer Searching File Not Found BASIC
I feel like I'm close to getting this working, but I'm not sure what to try next. Any help would be appreciated.