So far have repaired most of the key switches which had failed. Repaired damaged traces and removed most of the corrosion. Installed sockets for all the chips on the board. The system now will power on and a have access to the monitor but can't load BASIC.
The issue appears to be with BASIC3 as the Monitor returns F0 for all addresses from B000 to B7FF. Did a Dump of the ROM and its contents appear okay? Maybe the problem is with BS2 on Pin20, U16 7404 pin 11 is constantly High so pin 10 is LOW, will look at U17 74LS139N but I don't have a spare, so I hope it is not the problem. Any other suggestions?
Is it possible that while removing the chips and installing sockets it is possible you may have damaged some lands or other traces? A bent pin somewhere? Corrosion on the chip leads?
Seems a bit strange as F0 would mean 1111000. It's not likely you'd see that coming from an 8bit memory chip so it looks like the ROM is not getting addressed at all. Check all the address lines to make sure they make sense when addressing the ROM.
Box stock Superboard II Rev. B
KLyball replica 600D, replica 610 & KLyball Data Separator
OMS SBME and SBME+ memory cards
OMS Digi-Mule expansion bus
KLyball memory card
Thanks for the good advice. I have checked the continuity of all the addresses and data lines. Next, I will use my oscilloscope to check the actual signals for the addresses and inverted address signals, then I look at
74LS138 decoders and 2114 RAM (testing with only two RAM chips installed).
Problem with U17 74LS138 BS2 signal, so replaced the 74LS138 and now BASIC will load. Now investigating why the system only sees the first two RAM chips. Maybe an issue with /RS1 or /RS2 signals but is great progress. This poor system spent over twenty years in my brother's garden shed so it is wonderful to get this far. The last time it was powered on and working was in 1983. https://youtu.be/-slbms3Vfxo