TL074/TL072 work fine. Glad the schematics have made it to KO4BB.
I'm not too sure what the voltages should be at those test points. I would strongly suggest tying to find a GPIB adaptor somehow as it makes this debugging quite a lot easier. I had problems with the error log getting too long to find the latest errors.
Even if the traces looks like they are connected make sure to check them with a multimeter for continuity.
Simon
