Frequency Counter: Logic Schematic
The lower schematic is a pretty standard bidirectional rectifier together with capacitors and a 7805 as a fixed 5V source which supplies all the electronic in the frequency counter. For "security reasons" a fuse is used.
The upper diagram shows the main microcontroller, an ATMega161, connected to all the other boards via various cables. JP9 (reset) and JP2 (SPI) are connected to the 9pin SUB-D service port at the back side. The large gate HC30 turned out to be a design flaw and was not mounted into the socket. The strange wire connections around it are due to ease signal routing on the PCB.
The HC753 octal transparent latches save the current LED status of most LEDs on the front panel. The keys on the front panel are connected via JP1. The other connectors are well described in the schematic.