| Electronics > Repair |
| Please help power supply dead 110V to 24vdc 5vdc |
| << < (4/6) > >> |
| viperidae:
By the looks of it, you need to do something with the pwr on/off pin to turn the triac on. |
| timenutgoblin:
Near the top of the PCB, I can see a green-coloured component glued to the common mode choke. Is that a thermistor? Could it be open circuit or measuring high resistance? The O.P. measured 20Vac at the input of the bridge rectifier which may indicate a fault in the primary side of the PCB. |
| shakalnokturn:
You apparently don't know enough to be making live measurements on this, however those who survive learn. As previously mentioned by Haenk and others, there's a On/Off control, the best would be knowing how this is controlled and testing accordingly. My bets are on a failure of that part of the PSU rather than the rest. If you don't know how the On/Off is controlled (via host computer's USB 5V or seperate standby supply in printer?) you can check the supply by shorting A1/A2 power pins on QT1 triac. If your secondary voltages appear either your lacking the On/Off control voltage, or that portion of the PSU is defective. (QT1, R3 to R7, PC2, R1, R19.) |
| timenutgoblin:
There are 2 things that I've learnt about Switch Mode Power Supplies: 1) They usually require an external load to be applied to the output rail(s) for them to operate. This is especially the case with some ATX power supplies found in computers. Some ATX power supplies need to be connected to a HDD for them to operate. 2) They sometimes require an external signal to enable or disable them such as your SMPS. As shakalnokturn suggested, try shorting the 2 pins of the triac QT1 that he refered to. Doing this should result in the 110Vac being applied to the bridge rectifier. |
| transistor12:
Need to start externally. At output terminals there written PS_ON , look carefully . |
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