About Z14 (Vz = 11 V in the latest schematic)
@PiotrMisiuna Any marking on the zeners ?
Minimum PWM controller startup voltage depends on IC reference :
UC3842 & UC3844 : 16 VDC : Z14 value is underrated, PWM controller will not start
UC3843 & UC3845 : 8,4 VDC : Z14 value is OK
Interesting sentence in chapter '
7.3.5 Undervoltage Lockout' of the datasheet :
During normal circuit operation, VCC is developed from auxiliary winding NA with DBIAS
and CVCC. At start-up, however, CVCC must be charged to 16 V (*) through RSTART. With a start-up current of 1 mA,
RSTART can be as large as 100 kΩ and still charge CVCC when VAC = 90 V RMS (low line). Power dissipation in
RSTART is then be less than 350 mW even under high line (VAC= 130 V RMS) conditions.(*) Actual minimal startup voltage depends on IC model, see above.
Reminder : as PiotrMisiuna is located in Europe, VAC = 240 V RMS @ 50Hz (hence DC rail voltage = 339 VDC)