I knocked up this Rom replacement that can hold four different ROM images if I want to fit a selection switch. The image in my ROM is Tychie that I assume works if someone can confirm that. It works better than the original ROM chip that my programmer thought had four dodgy pins but it hasn't fixed my QL. I say it works better because during boot the screen gives a white panel on the bottom of the screen but it is only there for a flash where as the original ROMs just gave rubbish that was always the same. The transistor inverts the ROM select line and works nicely on the scope so no chip required. I enable the EPROM all the time because it takes less power than the old ROMS when not selected and the other select line is just an address line for upper or lower old ROM. I thought it was a simple build and didn't give it much thought on the assembly side so I put things on the board in the wrong order but luckily realised before I had soldered many pins on the socket. I had to push some of the pins out of the plastic socket to get it off again so I could cut the tracks and do anything under the socket before fitting it. The row of pins under the socket had to be soldered first then fit socket then other row of pins and be careful of not putting too much solder to join the cut tracks between the socket and row pins but I managed it in the end.
Here are some pictures of top and bottom. The space on the right I thought might be useful for a ram up grade but it can always be cut off later if not used.
Is there software that I could boot that would test for any board faults and give simple output like flashing an LED or something that doesn't require the screen?
I had to push some of the pins out of the plastic socket to get it off again so I could cut the tracks and do anything under the socket before fitting it. The row of pins under the socket had to be soldered first then fit socket then other row of pins and be careful of not putting too much solder to join the cut tracks between the socket and row pins but I managed it in the end. 