Completed work on testing the Extender Board and I/O board with the ZX81. The board burst into life after just less than 60 minutes of testing and repairs and it appears that the problem was that the chips had been put into the wrong sockets at some point over 30 years ago. Of course i did not have the edge connector then so never found that out at the time! At least it was easily rectified. If the chips had been damaged due to being in the wrong sockets i did have a few spares that i could have used. Successfully ran a small test program to confirm all the outputs of Port B of the 8255 could be toggled. Click here for more details.
Allan Faulds is an Electronic Design Engineer who develops Hardware and Software on a professional basis. He has a strong interest in applying his design and development skills to his areas of interest such as bicycle lighting and plant growing and greenhouse and garden control technology.