Because the external cassette port is not responsive (no power) I used the internal cassette port to load a cassette program, located near where the power connector attaches to the motherboard from the transformer. The internal port is called TAPE 2. Click image for larger view.
NEXT - trace the fault and repair. Because TAPE 2 works fine, the electrical fault is probably isolated to the cassette TAPE 1 5V circuit. At least I'd say that's the first thing to check.