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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?

Video of system power up https://youtu.be/2f-G8uNm9Gg

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.

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).

Thanks, BillO for the first time since February 1983 my Superboard II Model 600 Rev B has started BASIC.

Nice to see!

What did the problem turn out to be?

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

Hi Roy,

Nice to see it working.

Do you need any new key-switches?
I have a few new ones here in the shack somewhere...

Cheers,
Leslie