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80 HP 912UL will not start

in 912 / 914 Technical Questions 10 years ago

  • Re: 80 HP 912UL will not start

    by » 9 years ago

    Have you seen any drop in capacitance for the 47uF electrolytics?
      
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  • Re: 80 HP 912UL will not start

    by » 9 years ago

    The unit that I took apart had a bad solder joint on the end of one of the power resistors and the small SMT transistor on the back was faulty.

    All the capacitors measured OK. When I first took it apart I convinced myself that the problem was likely to be the electrolytics but they both measured OK with a low ESR. The main 400V cap measured OK.

    I exercised the trigger circuits and recorded some scope traces. I contemplated building a test fixture to run it up properly but other commitments got in the way ;-)

    I would be interested to see a photo of the back of one of the units that has been repaired to see what area they were working in.

    Kevin
      
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  • Re: 80 HP 912UL will not start

    by » 9 years ago

    I'd imagined that the fault was common across all failed units, as is often the way... but if not, this would make things a little more complex :-)

    Unfortunately I don't have a repaired one to look at. But I know that the back gets cut out, a repair is done and the back is re-potted... There is no resultant bulge in the back, so nothing big is being added.

    I'm almost tempted to send mine off to find out... but it's all black potting, so would need to x-ray it.
      
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  • Re: 80 HP 912UL will not start

    by » 9 years ago

    Do you know if the units supplied these days are exactly the same design? Is it an age they get to when they fail, or has the design been updated and improved the failure rate?
      
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  • Re: 80 HP 912UL will not start

    by » 9 years ago

    From what I have heard most of the failures are not the early units with the 4 pin plug and the bullet connectors but the later ones with the two 6 pin plugs. I don't know anything about the very latest units.

    I have only ever looked inside the one unit so I can't comment on the others.

    Kevin
      
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