How Come There Are So Many Optoisolator ICs In SMPS?
It is common to see 1 or 2 optoisolator ICs in a switch more power supply board (SMPS) but what about 3 or even 4 opto ICs in the power supply board? As far as I know those Opto ICs are use for over voltage and over current protection, regulation/feedback and also to use as a way to control on/off power by the MCU. It depends on the designer what pupose they want to put into the power supply circuit. The best way to understand the purpose of those ICs is to analyse it with the help of a schematic diagram. If you can't find the schematic then the only choice you have is to do it the hard way which is to analyse the circuit on your own.
It will take up your time as you need to trace at where the signal is coming from and where it goes. If the power supply is using 3 or 4 opto ICs and if one of the signal to those ICs is bad the the power supply could have shutdown, low power, power blink and even no power symptom. It is not easy to troubleshoot this kind of problem as you really need to find out which OPTO IC that need to get the first signal before the other opto ICs kicks in so that the full power from thepower supply can be produced.
No matter what SMPS you are repairing, always have the orginal load connected for easy troubleshooting. Some SMPS designs seems to have a brain (with the help of feedback circuit) and whenever it detects no load or wrong load it tends to shutdown after power up. In order to eliminates any weird problem in the power supply, always connect it with the original load. If with the original load the power supply still would not work then at least you now know that the power supply is the cause of the problem and your concentration should be in the power supply assuming the load is in good condition.