8th January 2021
While waiting for the parts and PCB's to arrive for ROMXe and ROMXc, I finally got to build and test the 2513 character ROM replacement for pre-rev 7 motherboards - and it works! My test machine is an Apple II (not a plus) with a rev 4 board in it :
It's the pride and joy of my collection - maybe one day I'll be lucky enough to have a Rev 0 machine, but it seems increasingly unlikely. Before installing ROMX and the 2513 board set, I had to repair a fault with the machine - the vertical sync circuit was not working correctly, resulting in a fast vertical roll of the picture. Using Jim Sather's excellent book Understanding The Apple II for reference, I was able to determine that gate 1 on the 74LS02 at location B14 was the culprit. This was confirmed in a logic tester :
Once that chip was replaced, and the machine was running normally, I set about installing the board set.
If you recall (way back in October) when I designed this board set, I wanted to have the identical text ROM functionality as a Rev 7 machine, with no motherboard mods required. To achieve this, I ended up with a 2 board solution that picks up the various required signals on the motherboard via the IC sockets. No bodge wires, and completely reversible.
First up is the 2513 replacement PCB which also taps into signals at location A3 :
And then there is the U-Board PCB which taps signals from the chips at locations B9 and B11:
It woud have been a nightmare to line up if it also had to plug into the B10 socket, so I worked around it in a U shape. Rather than reusing the A3, B9, and B11 chips I decided I'd just include SMD versions on the relevent boards. The U-Board links to the 2513 board via a U-Link cable, and the 2513 links to the ROMX board via the regular ROM-Link cable.
Installation went pretty smoothly - perhaps a little bit tricky to get the pins all lined up (mostly because I haven't yet made an assembly jig for this board set to ensure the headers are correctly aligned when soldering them in) , but otherwise no problems.
This particular machine has the (then) stock Integer Basic ROM set installed, with no D8 or D0 optional ROM - made it easy to install ROMX as I only had to remove the 74LS138 at location F12 :)
As this machine has an Apple Language Card installed, the Language Card mod is required to prevent the F8 Autostart ROM on the Language Card from overriding ROMX.. The 2513 and U-Board are hidden underneath the keyboard area so all you really see is ROMX and the ROM-Link cable.
End result is that we now have a tested solution for the pre Rev 7 motherboards. It uses the exact same flash image as the 2316B replacement so you have the exact same set of 16 fonts available.
Drop us a line if interested in one of these bundles. Oh - we've started a Slack channel #romx - link is also up the top right next to the twitter and facebook links (which currently dont go anywhere - working on it!). The Slack channel is a great place to ask questions, give us feedback, request new features etc.