Yeah!! Finally a SCELBI 8B is working like it was meant to be with TTY and cassette interface. This may be the only working fully configured SCELBI 8B in the world at this moment.

After much investigation, which I’ll document more fully in later posts, I finally figured out the problem with the SCELBI cassette interface. Turns out that the problem was on the write board. The .02 uF capacitor on the inputs to Z14 (pins 3 and 4) was creating problems with the counter at Z4, which uses the same clock. Apparently due to the altered shape of the clock, the counter was not counting properly. This created chaos with the written data. I changed the capacitor to .004 uF and everything started working perfectly.

Once I made this change, I just slightly tweaked cassette player volume and I was able to write and read a small buffer of all zeros and another of all ones. I was also able to write a 2K buffer of random data and read it back without any parity errors. I need to do some more testing and tuning, but based on this initial experience, I’m expecting that this interface will work pretty well in practice.

I’ll need to take a breath and figure out board prices, which will be similar or less than the TTY board and then, at last, I’ll be able to start shipping cassette PCBs.

Here’s a picture of my current SCELBI 8B setup, with TTY card, Cassette read and write cards and RS-232 dongle all attached. The TTY and Cassette cards will eventually be moved to enclosures with female 78S11 Amphenol connectors. These will be connected with standard SCELBI 11(really 12) conductor cable with male 86CP11 Amphenol connectors on both ends to the chassis.

SCELBI loaded up with I/O