I posted a preliminary copy of the cassette read and write board BOMs back in this posting.

Further investigation into the problem with the cassette write board reveals that the original SCELBI’s used revision A of the 7493 counter ICs, while I had purchased the original version. There seems to be significant differences in the specs, so I ordered a few 7493As to try. I’m fully expecting that the write board will work fine with the A revision parts, without having to change the capacitor. I have had very few problems with SCELBI designs in the past. I think that the inclusion of 7493As in production boards instead of plain vanilla 7493s was probably intentional, possibly to avoid the problem that I encountered.

The other change that is likely, is do to another image of the schematics that were sent to me. This version of the schematics have parts numbers labeled on the transistors. The image I received wasn’t all that clear, but the PNP types appear to be 2N2907 and the NPN types 2N2222. I doubt that the use of 2N3906 and 2N3904 on my reproduction in their place makes any difference, but I intend on updating the BOM.