hi Lorne.
As the fault is obscure, I would suggest the following.
1. Disconnect the two 10K resistors from the 4553 pins 1 and 2.
2. Connect the first transistor 10K directly to 0V [ so the LEFT transistor is always ON]
and the other 10K to +V [ so the RIGHT transistor is always OFF]
3. Disconnect the four wires to the 4543, pins 5,3,2,4
4. Connect the four pins of the 4543, pins 5,3,2,4 to 0V [ this makes the input = to a "0"]
5. Now switch on the power to the pcb.
6. The left LED should display a "0" [ the right LED should be OFF/blank]
Tell us what you see.
If it does display a "0" ok then
7. Disconnect 4543 pin 5 from 0V and connect to +V via a 10K resistor.
The LED should now display a "1"
Tell us what you see.