billdeg
Technician
Found and scanned this from the "TRS 80 microcomputer technical reference handbook" - a garbled characters "isolation flowchart" to help narrow down the cause of the problems. I tested, it seems to work pretty well as a starting point for repairs.
http://vintagecomputer.net/tandy/trs80_1/TRS80m1_GarbledDiagChart.pdf
Bill
http://vintagecomputer.net/tandy/trs80_1/TRS80m1_GarbledDiagChart.pdf
Bill