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Thread: NAD AV 716 no display

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    Default NAD AV 716 no display

    Got a NAD receiver to fix. The fluro type dislay doesn't light up. Voltage ok,resoldered connections. Now I'm stuck.



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    Heres a manual which should help.



    The first two and last two pins on the fluro display should have some AC volts on them to drive the display filament and the rest of the pins should have -20 to -30 on them.

    Check the capacitors c708, c709 and c710 these could upset the negative volts to the display driver.



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    So did you figure out what's wrong.




    Mickstv
    Last edited by mickstv; 14-03-11 at 10:18 PM.

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    Yes aware of AC on first and last two pins. Measures 4.74vac. Thanks for manual,gonna take time to read that. The caps tested fine and replacing them made no difference. I,m getting all postive voltages on other pins though,between 2.2V and 3.3V roughly. Thats measured with negative to 0V. Possibly doing that wrong?

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    Check page 24 and have a look around the capacitors you changed you should have -30 volts heading into the display driver IC make sure thats ok.




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    Getting no where on front panel PCB so removed bottom to access main PCB and power supply circuits. Soldered up dries around regulators etc,still no go. Started checking diodes,caps and resistors. Found open circuit resistor in series with AC-3 power feed.

    Its R921,and there is another R922(both 0.47ohm 0.5W). Now to try and find where to buy one. Would these be fusible type resistors? They are pale in colour(cream)and run warm going by other beside it.

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    They will be fusible resistors.

    Wonder why they are o/c. It might pay to check the main diodes and transistors in that section again just in case.


    That manual has been downloaded more than 10 times since I uploaded it and not one person has hit the thank at the bottom of my post. Thank everyone......


    Mickstv
    Last edited by mickstv; 15-03-11 at 05:09 PM.

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    Just one of them are OC. Didn't know about the "thanks" button,have hit it now.

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    Quote Originally Posted by NZ Alarm Tech View Post
    Just one of them are OC. Didn't know about the "thanks" button,have hit it now.


    I would replace both of them just to be safe. Generally if one is o/c on the AC side the other one would be stressed and likely to fail.

    Also I wasn't having a go at you mate I was having a go at the other users that decided they need the manual as well.



    Mickstv
    Last edited by mickstv; 15-03-11 at 05:40 PM.

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    your VKK must be -30V. CHECK THAT FIRST

    thats about the only hint, other than that...


    take it to a tech and pay him accordingly, he may then feed his family!
    When I explained to the guy what avatar I wanted, that wasn't what I meant!

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    Quote Originally Posted by iwacelect View Post
    your VKK must be -30V. CHECK THAT FIRST

    thats about the only hint, other than that...


    take it to a tech and pay him accordingly, he may then feed his family!
    Bit old now considering i've already told him and he's found a o/c fusible resistor in line.




    iwacelect, we can blame the internet and the likes of ebay for making information and parts so freely avaiable.





    Mickstv
    Last edited by mickstv; 16-03-11 at 07:47 AM.

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    I'm an Alarm Technician and have been an electronics enthusiast all my life. I fix other peoples gear to earn extra dollars to feed my family(1 income by the way). I prefer to buy low cost broken items and repair for myself though, Also love making things so plenty of projects on the go. Training myself has never been easy and now pay good dollars for information/contacts via internet. Willing to help others too as I dont charge full price for my practise on other peoples gear. I do take my electronics to experienced tech's when required.

    "your VKK must be -30V. CHECK THAT FIRST"

    OK,what does VKK stand for please. Thanks for the info.

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    Did you have any luck finding .47 if not get some 1 ohm fusibles if they are easy to come by and put them in parallel.

    EDIT : don't worry about VKK all you need to know is that you need -30 to drive the display which comes from the powersupply and goes to the driver ic.



    Mickstv
    Last edited by mickstv; 16-03-11 at 11:39 AM.

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    Thanks for idea. I will order them from Tradetech but need to make up an order of more than a few fuseable resistors. Shall start others posts for other amps to help fiqure out parts required.

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    Quote Originally Posted by NZ Alarm Tech View Post
    Thanks for idea. I will order them from Tradetech but need to make up an order of more than a few fuseable resistors. Shall start others posts for other amps to help fiqure out parts required.


    Do you have anyone local that fixes stuff that you could get them from maybe. Or maybe some junked boards that may have the resistors on.




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    I've got other values from junked boards. I have tested it with a fuse and all lights up with the -30 volts so yippee. Have moved on to the next job. Many thanks!

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    Quote Originally Posted by NZ Alarm Tech View Post
    I've got other values from junked boards. I have tested it with a fuse and all lights up with the -30 volts so yippee. Have moved on to the next job. Many thanks!


    Good stuff.

    The second hand ones were they definately fusible because as you would know if you don't use fusible resistors you could have a risk of fire.




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    Last edited by mickstv; 16-03-11 at 05:21 PM.

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    Default Update:

    Got new pair of fusible resistors and installed. Turned on and all ok. Put it all together, difficult being so long since pulling it to bits(all those screws)but got there. Thanks for the help.

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    Quote Originally Posted by NZ Alarm Tech View Post
    Got new pair of fusible resistors and installed. Turned on and all ok. Put it all together, difficult being so long since pulling it to bits(all those screws)but got there. Thanks for the help.

    Another job well done.




    Mick

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    Question i find both R921 and R922 busted, please advice

    Quote Originally Posted by NZ Alarm Tech View Post
    Getting no where on front panel PCB so removed bottom to access main PCB and power supply circuits. Soldered up dries around regulators etc,still no go. Started checking diodes,caps and resistors. Found open circuit resistor in series with AC-3 power feed.

    Its R921,and there is another R922(both 0.47ohm 0.5W). Now to try and find where to buy one. Would these be fusible type resistors? They are pale in colour(cream)and run warm going by other beside it.
    I'm not a techical guy. I also have a NAD AV716, and my problem is as same as yours, so I first checked and found the 2 bad resistors.

    BUT could anyone please tell me which components will most likely go wrong even after I replaced the new ones? anyone has any problems again after replacing the R?

    thx a lot

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