Do not power your SBC until you've done some preliminary checks!

Use sockets unless you are confident you can make it work on the first boot!

Verify VCC and GND are present in all sockets per the schematic

Make sure power connector is attached properly (no reversals)

Add only the components you need to test a subsystem

Build only one subsystem at a time and test it before moving onto the next

You only need the CPU, ROM, memory decode logic, clock, RESET circuits for a minimally working system.  Do not insert other ICs or components until you need them!

Optional components are all connectors, Q1, ECB bus transceivers, RTC circuit, UART, PPI, RAM, and RAM MPCL.

Check VCC

Check GND

Check Clock circuit

Check RESET circuit

Look for solder bridges

Look for unsoldered joints

Look for cold joints

Clean up all the joints with solder wick and remelt

Use the diagnostic programs in the default software build such as JRLOOP, JPLOOP, SCREAM, HDM80, etc

Use a logic probe and/or oscilloscope to verify /MREQ and /IORQ are pulsing after boot