Fix DS1307 RTC Malfunction

The DS1307Z real-time clock on my custom PCB stubbornly reports nonsense values—think 00:00:80—and refuses to accept new time or date settings. Everything else on the board behaves, so the problem appears isolated to the RTC section.

Power to the RTC rail is rock-solid, and on the firmware side I have already combed through the code for syntax slip-ups and walked through the logic flow; nothing obvious stands out. I will share both the RTC schematic and the current firmware so you can trace the fault from hardware through to I²C transactions.

Here’s what I need from you:
• Pinpoint the exact cause of the malfunction, whether it sits in the circuit, the layout, or the code.
• Provide a concrete fix—this could be a schematic tweak, a board-level bodge, or patches to the firmware, complete with clear implementation notes.

Acceptance is simple: after applying your solution the clock must set, keep, and report the correct time across power cycles and battery backup. A concise write-up of the root cause plus the corrected schematic or code diff will wrap it up.