Soviet digital clock Elektronika B6-403 (Электроника Б6-403) was produced in USSR from late 1970s to mid 1980's.
The schematic is almost identical with Elektronika 4 / G9.02 clock.
It was based on 4 single digit VFD displays with 21mm digit height in a glass tube envelope similar to a vacuum tube or nixie.
7-segment displays are IV-12 (ИВ-12) and the separator is IV-1 (ИВ-1).
Transistors are KT361D (КТ361Д). Integrated circuits (CMOS):
1x K176IE5 (К176ИЕ5) - Crystal oscillator with prescaler from 32768 Hz to 1Hz, 2Hz and 64Hz.
3x K176IE4 (К176ИЕ4) - Base-10 counter with 7-segment output (similar to 4026).
3x K176IE3 (К176ИЕ3) - Base-6 counter with 7-segment output (probably doesn't have any western equivalent).
1x K176LA9 (К176ЛА9) - Triple 3-input NAND gate (similar to 4023).
Clocked by 32768 Hz crystal.
The clock has 4 buttons: Reset minutes, Set minutes, Set hours and a selector of two levels of brightness.
The power consumption is 1.5 - 2.5W from 220V 50Hz mains. 9V backup battery can be connected.
Common failure is short circuit in one of 25 transistors (KT361D), that switch the segments of VFD displays.
E-C short causes permanently lit segment, E-B short causes permanently off segment. Electrolytic capacitors also may
dry out or the VFD displays may wear out (brightness declines or gets uneven). The clock is built for 220V mains. In 230V or 240V countries
the VFD heater filaments can suffer from overvoltage. This can be solved using series resistor cca 0R15 for 230V or 0R3 for 240V to set the heater
voltage as close as possible to nominal 1.5V~.
