Elektronika 6.15 (Электроника 6.15) alarm clock was produced in USSR during 1980's.
It was built with flat 4-digit 7-segment VFD display IVL1-7/5 (ИВЛ1-7/5) or ILC4-5/7L (ИЛЦ4-5/7Л) with 21mm high digits.
Integrated circuits (CMOS):
K176IE18 (К176ИЕ18) - Crystal oscillator and prescaler. Older versions of the clock may contain K176IE12 (К176ИЕ12). This one doesn't allow 2 levels of brightness.
K176IE13 (К176ИЕ13) - Clock circuit (24h mode, 4-digit).
K176ID3 (К176ИД3) - BCD to 7 segment decoder. The oldest version uses K176ID2 (К176ИД2) and has two extra K161KN1 (К161КН1).
The clock is controlled by 32768 Hz crystal.
Accuracy according to manual is 1s/day at 20 +/- 5 °C, 5s/day at 5-40 °C.
Mains voltage 220 +22/-33 V, 50 +/-1 Hz, power max. 6VA. Max. backup time with 9V battery is 240h. Alarm intensity min. 65dB at 0.5m.
I measured the power consumption to be cca 2W.
How to use the clock:
Control buttons at the rear panel (from left to right):
1. "Show alarm". A latching button. When latched, alarm time is displayed. Use buttons 2 and 3 to set alarm. When unlatched, time is displayed.
2. "Set minutes"
3. "Set hours"
4. "Reset minutes". This will set minutes to 00. The design of this clock requires you to press this button after plugged in, before setting the time!
5. "Brightness". Selects low or high brightness. Mind that the clock can only be set when high brightness is selected! The brightness selector is omitted in some models.
- Big latching button at the top of the clock. Latch the button to disable alarm, unlatch it to enable alarm.
Common failure is one of the three CMOS IC's. Electrolytic capacitors also may
dry out or the VFD display may wear out (brightness declines or gets uneven). The clock is built for 220V mains. In 230V or 240V countries
the heater filament can suffer from overvoltage. This can be solved using series resistor (see below).
Also the crystal tends to fail, it can cause very inaccurate run or dead clock.
