I got these from C. Singleton a year or two ago and just noticed raw copies are floating around here. Optimized, OCR'd, and indexed versions are posted on my site if anyone wants. I have tons of other stuff I still need to process and a bunch more to scan for various GRiD models.
https://classicbits.net/library/ then go to GRiD > Portables > 1500 Series
GRiD_965018-00_GRiDCase-1500-Series_Hardware-Service-Course_(May-1988).pdf
GRiD_001500-50_GRiDCase-1500-Series_Hardware-Technical-Manual_(Oct-1988).pdf
GRiD_001500-60_GRiDCase-1550sx_Service-Manual_(Jun-1991).pdf
https://classicbits.net/library/ then go to GRiD > Portables > 1500 Series
GRiD_965018-00_GRiDCase-1500-Series_Hardware-Service-Course_(May-1988).pdf
GRiD_001500-50_GRiDCase-1500-Series_Hardware-Technical-Manual_(Oct-1988).pdf
GRiD_001500-60_GRiDCase-1550sx_Service-Manual_(Jun-1991).pdf