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Thread: Hitachi a100 power supply

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    Default Hitachi projector a100 power supply

    Hello,

    I have received an old Hitachi projector a100 that doesn't power on, no lights no nothing. This is pretty much been narrowed down the the power supply.

    There is no standby power, 240v can be measured up to the bridge rectifier. Where would be the best place to start looking as im no expert on power supplies and as this has half the underside covered by a glued in common transistor heatsink. Its hard to have a good look :/




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    Last edited by TheTodd; 30-05-17 at 08:23 PM.



Look Here ->
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    Default

    Top view


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    Without the relevant experience, your task is going to be difficult.

    Personally, I am a little reluctant to offer advice regarding switchmode power supplies (PSU's) to inexperienced people, as they can receive a nasty shock from one or suffer even worse consequences.

    Be warned that the high voltage filter capacitor on the output of the bridge rectifier (with 240V DC on the input) can be charged to 340 volts DC or thereabouts and should be discharged before poking around.

    The capacitors shown in your pictures do not show any obvious signs of "bulging", a common sign of a faulty component, therefore the problem could be in the swtichmode IC, any of other the diodes on the PCB or various other components. But the absence of "bulging" is not always a reliable indicator.

    I suggest enlisting the aid of someone who is suitably qualified to trouble-shoot the problem for you.

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    Thanks for your concern, I'm more then aware of the risks, and the potential voltage. The capacitors all seem perfect, no swelling, coming off the board or shorting. The fact that there is NO voltages coming makes me believe they may not be the issue.

    And the fact I am inexperienced in PSU's is the reason WHY i want to trouble shoot, if i don't know, i learn.


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    There are service manuals for the scanner in question available at several websites (for a fee). I could not locate any free ones. See and .

    And the fact I am inexperienced in PSU's is the reason WHY i want to trouble shoot, if i don't know, i learn.
    It's good to want to learn, but the starting point and method by which you go about this is largely determined by your current level of expertise. After all, one has to learn to crawl before one can learn to walk.

    If you want to learn about switchmode power supplies there are numerous sites where such information is freely available, such as those returned by .

    A basic knowledge of switchmode PSU's is required before you contemplate attempting to troubleshoot and repair one, particularly if there are no obvious physical signs of where the problem lies, as appears to be the case here.

    Now, I'm not trying to be difficult, but do you have any formal (or even informal) electronics experience/qualifications to aid you in this endeavour?

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    20 years or more of repairing Tv`s,computer, Game, appliances, console modding, dabble in car repairs and once had a small business repairing iPhone's before the markets got flooded with schoolkids with cheap ebay parts so yes i do know my way around a soldering iron, and i have already spent the last week researching PSU`s.If your wondering why im asking for help with this, is this is logically more technical then what i usually fix, and i REALLY don't want to have to desolder the 5 components underneath just to inspect the bottom unless there is no other option.

    I could just go on Ali express and buy it new,but I though HELL, lets fix this guys up and learn something along the way.

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    Quote Originally Posted by TheTodd View Post

    There is no standby power, 240v can be measured up to the bridge rectifier. Where would be the best place to start looking as im no expert on power supplies and as this has half the underside covered by a glued in common transistor heatsink. Its hard to have a good look :/
    First make sure that huge cap is fully discharged which is hard to confirm without removing that heat sink. It can hold voltage for weeks when the PSU is faulty.

    Wear rubber gloves!

    Your best bet is to CAREFULLY check the 10 large soldering pads of the components attached to the heat sink against each other to ensure there is no voltage. They are easy to access on the component side. I assume that that 4 legged beast attached to the heat sink is the bridge rectifier.

    Then check there is no short on the secondary (low voltage) side. Usually it is a rectifier or a cap gone short. You do not see that from bulging caps.
    On the second photo copper side there is an 8 legged smd IC on the left of the unexposed area (still mains) that could also be the culprit.
    You really can't check the IC without a replacement but you can passively check every component around it with a multimeter. Caps with ESR meter if possible.

    The two opto copplers in the gap between mains and low voltage are also worth checking. If the diode side is conducting with a multimeter the photo transistor side should conduct with a second multimeter also on diode test correctly poled of course.

    Finally you will have to bite the bullet and desolder those 10 pads that hold the heat sink and check the 'transistors' for shorts at least.
    You can not do that when they are soldered in because the transformer coils are shorting your multimeter. Diligently check the copper tracks and solder joints for fatigue because here is where the most (heat)stress is.

    Good luck and only do these tests without any power connected.
    Last edited by Uncle Fester; 02-06-17 at 12:27 AM.
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    Hey thank you, ill check this out on my next day off,

    I have a couple of questions too,

    The times i have pulled this out after 240v testing, i shorted out the main filter cap but there was no crack? can this be a fault of simply that the board is setup to discharged when turned off?

    All the guides and pages ive read often talk about a large and a small Transformer to supply the main and secondary power, In this case is one transformer supplying the main board power and second one supplying the power to the lamp driver board? the projector does have standby mode. again hard too see under the heat sink.

    And what is the purpose of the big IC board that sticks up right next to the main filter cap, is this just the timing chip for the transistor or more?

    thank you again.

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    It sounds to me as if the main filter capacitor, at the output of the bridge rectifier could be open circuit/low capacitance/leaky.

    I have sometimes found this to be the case.

    Remove from the pcb and check the capacitor with a capacitance meter or ESR meter.

    If the capacitor is O.K. the indications are that something is pulling it down to ground.

    Not being familiar with the projector circuitry and PSU in question, it is difficult to answer your other questions.

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    ah,that could be it, I will try that after everything else as i will need to remove the bottom Transistor group to get to it.

    also here is the diagram if you wish to look, FYI the quality is not my doing it is literally how it is was printed in the service manual

    thanks, again.





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    Quote Originally Posted by TheTodd View Post
    Hey thank you, ill check this out on my next day off,

    I have a couple of questions too,

    The times i have pulled this out after 240v testing, i shorted out the main filter cap but there was no crack? can this be a fault of simply that the board is setup to discharged when turned off?
    Something in the circuit can discharge it fairly quickly and it should if it is not faulty however a small voltage under 15V should be still measurable for a while.
    Totally zero almost immediately would indicate a faulty or disconnected mains cap like Tristen mentioned.

    All the guides and pages ive read often talk about a large and a small Transformer to supply the main and secondary power, In this case is one transformer supplying the main board power and second one supplying the power to the lamp driver board? the projector does have standby mode. again hard too see under the heat sink.
    Kind of like that. The transformer with yellow tape looks like a boost coil to create the 380V for the lamps ballast but it also seems to supply the transformer for the low voltages.

    And what is the purpose of the big IC board that sticks up right next to the main filter cap, is this just the timing chip for the transistor or more?
    Looks more like the driver circuit for the main power mosfets, which I assume is indicated as MC101 in the schematic.
    Timing and feedback control is done in the circuit with that 8 legged IC I mentioned above where the optocopplers are intergrated.
    It would be interesting to know it that 9V is still present on the connector to the ballast P2 pin4
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    Well, decided to bite the bullet and de-soldier. The capacitor is reading about right so it seems fine. Here are some pics of the board.


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    So I've tested the smaller capacitors, they are ok, the mosfets ok, and the bridge rectifier is fine also.


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