welcome back to my channel, this 12 volt 20 ampere power supply have problem, that it have just only a few volts in the output instead of 12 volt and it have no control if you don't have a good practical experience in Power Electronics, never try to repair I will apply power using series lamp (100 watt Tungsten lamp) if you have isolation Transformer to power up this power supply that will much better we can see, the power supply draw current, the lamp indicated and then it turned off it is not turned off, it is drawing the routine current, the fan is off if I will check ac voltage here, at input terminal it is 229 volts and if I check DC voltage between positive and the return - Terminal it is just only 2.3 volts and if I try to adjust, it have no control it is not increasing or decreasing the voltage. let's check what is the problem now I will remove the outer four screws, here for the top cover two four and six now remove mosfet heatsink screw and this rectifier heat sink four screws here for the PCB. this solder joint is looking in some suspected look, in the first step verify DC voltage on these capisters, 160 millivolt that means it is safe if there are any voltage there never touch the board, until it is discharged now I will add jumpers here to apply ac voltage inspect the circuit carefully for any burning sign, smoke, damage it is using tl494 here but if we see this IC I think this IC have some crack or discoloration at this point in the first step I will apply power here because this power supply is starting up that means, its startup circuit is good now we want to verify this IC pin number 7 & 12. it have only 4.3 volts LED is on we have just only 3.5 volts in output but problem here at VCC pin number 12. it have only 4.4 volts, it is not good pin number 14 4.4 volts that means it have something wrong with the VCC. so this IC is making problem now if we verify the voltage on this DC rail 162 volts, this capacitor 162, that means both capacitors are good and the total voltage here, it is 324 volts that's good. that means no problem in DC rail. so problem here in this section. if we check this IC it have some crack or discoloration here and it have something wrong here yes it has something wrong here yes this is IC tl494.I will install it here I will apply some solder here for good thermal conductivity, so we can desolder it easily always solder or desolder randomly never solder or disorder IC with one sequence. if you will install in sequence, we will damage the IC. either we are installing new IC, we will damage the IC because when we are heating up in same line, the IC substrate will heat up and its internal connections will damage solder from different places. well I will solder this pin the other pin will cool down verify the rectifiers here now I am checking this transistor so it is good, this is good so it is better to verify transistors okay now I will install this IC now I installed the IC and now I will power up this circuit and we will see the result yes the LED is now bright, before this it was dim yes I have 15 volt, wonderful, that's nice we have now the control, that's good and voltage are stable if you enjoyed this video, hit the like button. I think this IC is material failure because other no component is damaged we can check the voltage here at pin number 7 and 12. it is 23 volts. that's good we have 23 volts 4.9 volt reference. that is good before this with this IC it was just only 3.4 volt I hope you enjoyed this video, if it is good. hit the like button if you have any question, please write in the comments. thanks for watching
