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    Please help power supply dead 110V to 24vdc 5vdc

    hello,
    this printer power supply is dead,I cant figure out with my limited knowledge that why the lower output part of circuit is not getting any DCV. I have measured voltages across transformer and I found 24v but nothing on the other side of transformer, please have a look at pictures, any help is kindly appreciated. thanks.

    Please, right click on image and open in new tab, for some reasons it will show up too big in this post










    Thank you

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    Re: Please help power supply dead 110V to 24vdc 5vdc

    U1 IC







    Updated readings and measurements.



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    Re: Please help power supply dead 110V to 24vdc 5vdc

    Hi,

    Seems to be something basic.
    Maybe FS1 is a fuse and is blown ...
    Unpower your circuit and check continuity of FS1.

    Klaus
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    Re: Please help power supply dead 110V to 24vdc 5vdc

    Two points to make here:

    1. You show DC voltages across the transformer primary and secondary, you can't measure these voltages with a normal test meter and they are not DC anyway.

    2. There will be very high voltages on the primary side, easily enough to kill you. Be extremely careful connecting anything to them, including testmeter probes and under no circumstances try to measure voltages from one side of the transformer to the other. There is a lines, roughly side to side through the 'varistor' (more likely a high voltage capacitor), through the transformer and then through the 4 and 8 pin optocouplers (PC1, PC2?) that divides the primary high voltage side from the safer secondary and isolated low voltage side.

    The first test to do is connect the AC power and measure the DC voltage across the 150uF/400V capacitor. It should have around 210V DC across it, if that is missing, either the input fuse is blown or the bridge rectifier has failed. If they are OK and the voltage is much lower, most likely the capacitor itself has failed.

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    Re: Please help power supply dead 110V to 24vdc 5vdc

    Quote Originally Posted by betwixt View Post
    Two points to make here:

    1. You show DC voltages across the transformer primary and secondary, you can't measure these voltages with a normal test meter and they are not DC anyway.

    2. There will be very high voltages on the primary side, easily enough to kill you. Be extremely careful connecting anything to them, including testmeter probes and under no circumstances try to measure voltages from one side of the transformer to the other. There is a lines, roughly side to side through the 'varistor' (more likely a high voltage capacitor), through the transformer and then through the 4 and 8 pin optocouplers (PC1, PC2?) that divides the primary high voltage side from the safer secondary and isolated low voltage side.

    The first test to do is connect the AC power and measure the DC voltage across the 150uF/400V capacitor. It should have around 210V DC across it, if that is missing, either the input fuse is blown or the bridge rectifier has failed. If they are OK and the voltage is much lower, most likely the capacitor itself has failed.

    Brian.
    i tested the cap 150uf/400v and there is only 24VDC across it when the ac power is connected. so i will see the bridge rectifier and then cap.
    thanks



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    Re: Please help power supply dead 110V to 24vdc 5vdc

    ntc could have gone open ckt - but more likely the low power ckt supplying the IC has died - hence the IC dead & main mosfet

    check o/p diode just in case this has gone short ...



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    Re: Please help power supply dead 110V to 24vdc 5vdc

    The big capacitor is fed directly from the bridge rectifier which in turn is fed through the filter and fuse from the AC input. It could be the NTC if that's what is hidden under the white silicone but to get 24VDC implies there is a high impedance path very close to the AC input connection.

    Imcool1, with the AC unplugged and the board left to discharge for a minute or so, use your testmeter on the resistance range to measure across the pins of FS1, then the green disc near the AC connections and tell us what you get.
    You could also measure from each of the middle two pins of BD1 to each of the AC input wires and tell us the resistance there too.

    *UNDER NO CIRCUMSTANCES DO THIS WITH THE POWER TURNED ON*

    Brian.
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    Re: Please help power supply dead 110V to 24vdc 5vdc

    Quote Originally Posted by betwixt View Post
    The big capacitor is fed directly from the bridge rectifier which in turn is fed through the filter and fuse from the AC input. It could be the NTC if that's what is hidden under the white silicone but to get 24VDC implies there is a high impedance path very close to the AC input connection.

    Imcool1, with the AC unplugged and the board left to discharge for a minute or so, use your testmeter on the resistance range to measure across the pins of FS1, then the green disc near the AC connections and tell us what you get.
    You could also measure from each of the middle two pins of BD1 to each of the AC input wires and tell us the resistance there too.

    *UNDER NO CIRCUMSTANCES DO THIS WITH THE POWER TURNED ON*

    Brian.
    hello, i measured more voltages, please have a look..




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