overvoltage switching power supply

I have a switching power supply for the Digital Receiver, according to which the output voltage is not reasonable. On the PSU PCB board listed 22 V and 3.3 V at the output, but after I measured it using a volt meter, volt meter that shows the number doubled is even more of which are listed on the PSU's PCB board. So that makes 2 Electrolyte Capacitors (220uF/35v) burst / leaking, then I replace both with the same capacity and voltage
I assume there may be errors in the AC (in the primary "Switching Transformer") on the PSU, then I started to check the components one by one, at that part there are two transistors (BU3150 and C6020), both transistors are good , an electrolytic capacitor which large voltage (22uF/450v) good too, then I checked a few other components, such as Diodes, Resisor, capacitor (non-polar), all of the components is good.
Then I checked the DC (in the secondary section "Switching Transformer"), there is an IC 4 pins (B1121  817C) and a non-polar capacitor with high voltage (222 M 400v), which connects the AC and DC good too, no which short linked. there is a transistor in the DC TL431 are also good

the question is, what lead to overvoltage on the output?

please help ..

regards

Is the overvoltage you are getting is regulated or stable, no matter how higher it is. if it is so then check the feedback circuitry comprising of TL431 and PC817 with some resistances and capecitances.
The output voltage regulation is mainly governed by the feedback circuitry and the TL421 along with its tunning resistances play a vital role in that.
TL431 is not a general transistor but a variable voltage regulator. Like in LM317 the regulation is governed by the two resistors, in the same manner , here also two resistors governes the voltage regulation.
Check the values of the two resistors which go from the first pin of TL431 to ground and + wire.
revert me with your observations