On transmit, 27MHz squarewave appears at pins 4 and 10 of IC3. (Should be ~7MHz squarewave, as observed on another QCX built by a relative.)
What method are you using to see this squarewave?
Is it the expected 3.3V peak to peak?
Is it a stable frequency?
Can you alter the frequency?
73 Alan G4ZFQ
This suggests that IC1 isn't being programmed to output 7MHz signals.
What I've done so far:
-- Visually inspected IC1 pins for possible shorts (for the second time; also did that before the board was assembled). None found.
-- Visually insected IC2 (microprocessor) socket joints. All look good.
-- Removed and reseated IC2. Didn't fix the problem.
-- Visually inspected traces on board bottom from IC2 socket to IC1. No problems found.
-- Performed a system reset. Didn't fix the problem.
-- Verified continuity between IC2 pins 27 and 28 to IC1 pins 4 and 5.
-- Verified that R3 and R4 are 1K.
-- Verified that voltage at output of D1 is 3.3V.