ERR 1 and then ERR 4 flashing
It is necessary to make measurements.
I think you have a problem with the signal level on A3.
You need to check:
1. Input BNC connectors. Cable from them to leak
2. R28 - loss of contact or poor contact.
3. Voltage to CR1, CR18
4. In А3 - ТР2, ТР3,
5. key Q2,3,4
6. the key Q10,11,12,13,14
7. carefully U5. Comporator LM339P she manages the keys.
you need to get passport modes on T3 and T6.
Remember that the common points are different!
I hope that the power supply voltage of the module is normal.
The following models did not use an operational amplifier. The discrete elements were installed.
Perhaps this is more reliable.