Dish motor doesn't move... Faulty motor or receiver?

Discussion in 'Satellite TV' started by Sat-du-Nord, Nov 7, 2010.

  1. Sat-du-Nord

    Sat-du-Nord Member

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    my dish stopped moving suddenly in a middle position on a way from Astra to Hotbird :(. I have tendency to blame the receiver as it happened to me already once with my previous Echostar that at some point in time just lost the Diseqc 1.2 function while doing everything else just fine. However it would be nice to be sure that it is really receiver and not the motor this time before I send the receiver off for repair (still under warranty).
    The symptoms:
    - the receiver works as usual, however motor doesn't move to neither satellite nor reference position
    - the receiver can see a bit of LNB signal when set to Astra and nothing at other settings (motor is stuck close to Astra)
    - the motor doesn't move when manual buttons East/West are pressed
    - 18V is still present on the coax
    - I checked the receiver with another motor and it was not moving as well. However, the big BUT is, I'm not 100% sure that this motor is still alive (any way to check it? I can open this one if it helps:smile:)
    The BIG question: is there a way to figure out who is dead, motor or receiver?
    MANY THANKS TO ALL HELPING!!!
     
  2. Robbo

    Robbo Satellite mad

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    Try another receiver.:smile:
     
  3. Sat-du-Nord

    Sat-du-Nord Member

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    Thank you for the advice! The only problem, I have no other receiver with functional diseqc:sorry:. Is there an independent way to check the receiver/motor? e.g. connect a resistor and watch for some signal when diseqc is accessed?
     
  4. Robbo

    Robbo Satellite mad

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    Possibly yes, as the disecq commands modulate the 22kHz tone. Problem is to check that they are working you would need to have an oscilloscope to check that the tone is being modulated, and secondly understand what you should be seeing. The easiest way to check the motor it is to use a receiver, any cheapo receiver that does USALS/diseqc1.2 would do. You can also buy diseqc positioners, but I believe it would cost more than a cheap receiver anyway.

    Maybe you could use a pc sound card to look at the 22kHz tone, but you've have to remove the dc and attenuate possibly too. Not ever tried it.
     
  5. Sat-du-Nord

    Sat-du-Nord Member

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    Yes, that's someting I can try. Do I understand correctly, that the receiver sends the commands via 22kHz modulation to the motor and the commands are interpreted by some sort of microprocessor in the motor to rotate. So, it should be some sort 22kHz pulses on top of 18VDC every time it sends a command, correct?
    However, as the motor doesn't respond to East/West buttons I don't think it is the (only) problem. Is it possible that the receiver cannot draw enough current to drive the motor? In other words, it it possible that 18V are still there, but those 500mA of current cannot be drawn due to some transistor/opamp failure? Can it be checked by shortening the leads through some resistor ("motor model") and measuring current?
     
  6. Sat-du-Nord

    Sat-du-Nord Member

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    Ok, I did the tests. In operating mode with the open circuit I have 18VDC and a 22kHz carrier with 0.7Vp-p. It looks like that (time scale 10us):

    [​IMG]
    When a command sent I see a modulation on top with a frequency of approx. 1kHz (time scale 1ms):
    [​IMG]

    I also tried to load if with 80 Ohm. It looks like the system is capable of sending the current through the resistor (dissipating 4W of power) without any visible changes in terms of DC or AC signals.

    THE QUESTION: is it enough to assume that the receiver is functional?
     
  7. Sat-du-Nord

    Sat-du-Nord Member

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    To finalize the story:
    The problem was localized to the motor side and fixed.
    The receiver happened to be fully functional and the whole system works fine again.
    Thanks again to Robbo for good hints and tips!:righton:
     
  8. Larry Laffer

    Larry Laffer New Member

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    Hi guys!
    I know it's an old topic but I'm in the same situation now.
    Can I ask you what exactly was wrong inside the motor?
    Or maybe a list of common faults if my sat motor won't move?
    Receiver and cables seems to be ok. My aluminium dish is 45 cm, so I don't think it's size and weight is the problem...
     
  9. pedro2000uk

    pedro2000uk Installer/Design Engineer

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    Check cabling and connectors for damage including water damage

    Check if lights are on on the motor (if it has any)

    Try buttons on motor if it has them

    Try reseting the motor from the receiver or at the motor but it should be at zero

    Check there is 13 or 18 volts on the sat output from the receiverest

    Decent motors usually last a long time when fitted properly, one thing that can damage them is electrical faults on any connected device putting voltage on the sat cables
     

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