problem oscilloscope philips pm3240

Discussion in 'General Electronics Chat' started by marketta, Dec 15, 2012.

  1. marketta

    Thread Starter New Member

    Dec 15, 2012
    6
    0
    hi
    I am Italian
    also I have an oscilloscopio PM 3240 that it doesn't turn on
    the problem is in the card feeding, and to a first analysis I have found that the filter of net F11801 is in short-circuit and the zener opened GR1835 and the resistance R1819 Da 2ohm open.
    I have still replaced the broken components but the oscilloscopio it doesn't turn on the tensions on the card feeding they don't go out of the relative connectors.
    Can you be that the IC is broken 1801 UA723s that don't furnish the tensions for the inverter?
    give me information for the reparation.
    thanks to all of you
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Do you have the service manual and schematics?
     
  3. marketta

    Thread Starter New Member

    Dec 15, 2012
    6
    0
    yes
    thanks
     
  4. MrChips

    Moderator

    Oct 2, 2009
    12,432
    3,360
    Something must be loading down the power supply and blowing components.

    The first thing I would do is a complete visual and smell test to look for all burnt components or bulging capacitors.

    Next, I would disconnect the power supply cables and plug it into the dummy load as shown in Fig. 3.42 on page 177.
     
  5. marketta

    Thread Starter New Member

    Dec 15, 2012
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    I will have to build him
    I will make you know
    thanks
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    You don't have to build it exactly as shown in the circuit diagram.
    Since this is a single AC transformer I would think that a simple load across any of the secondary windings should be sufficient.
     
  7. marketta

    Thread Starter New Member

    Dec 15, 2012
    6
    0

    hi
    I have tried to void detaching all the connectors of exit but the tensions they are all to zero
    as I have said I already suppose that the guilty one is the uA723 that you is broken for the damage of the components that I have already quoted.
    I have purchased uA723 when I replace him I will make you know.
     
  8. marketta

    Thread Starter New Member

    Dec 15, 2012
    6
    0
    after having replaced ua723
    from further analysis I have found R1800 from 3,3ohm open
    and the zeners gr1806(75volt) and gr1807(47volt) in short circuit
     
  9. marketta

    Thread Starter New Member

    Dec 15, 2012
    6
    0
    after having replaced the zeners gr1806(75volt) and gr1807(47volt)
    the oscilloscope has started over working -
    Now the problem is that during the calibration with the honest ones
    from the channel B doesn't go out the wave it squares the horizontal trace he is seen, only and if I send a signal with various levels of tenzione the trace he/she is firm.
     
  10. gootee

    Senior Member

    Apr 24, 2007
    447
    50
    First make sure that all power rail voltages are within specifications.

    Find the Vertical Amplifier circuitry for both Channel A and Channel B. The two sets of vertical amplifier circuits should be identical/same, or nearly identical/same, to each other.

    With Channel A and B front panel settings all the same, and the same input, every measurement anywhere in one channel's vert amp circuit should be the SAME as the measurement at the same (corresponding) point in the OTHER channel's vert amp circuit.

    Method to shorten time to repair: First measure at both vertical amp inputs and outputs. If inputs give roughly the same measurements but outputs do not, then measure at a location that is about HALFWAY through each of the two vert amp circuits. (Always measure at exactly the same, i.e. corresponding, locations for both channels.) If any pair of measurements has a significant difference between the two channels' measurements, then the problem is upstream, i.e. closer to the input. If a pair of measurements are roughly the same, then the problem is farther downstream, closer to the CRT circuits. Always choose the NEXT measurement location to be roughly halfway between the last-measured point and the end of the circuit, or the last measured point, in the direction where the problem is. If measurements are same, problem is farther downstream. If measurements different, problem is farther upstream. Using that "binary search" method, by always dividing remaining (unmeasured) circuit roughly in half, will usually result in far-fewer measurements than sequentially working through the entire circuit. Also, looking at the schematic will help, if you choose measurement locations at logical subsystem input/output points, until a subsystem containing a problem is discovered.

    If problem is not in channel B vertical amplifier, proceed to other sections of circuitry for which separate channel A and channel B sections exist, and use the same type of procedure as above.

    Cheers,

    Tom
     
    Last edited: Dec 30, 2012
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