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oscilloscope LEADER 4081= KENWOOD CS-5135 DOES NOT CHECK THE BRIGHTNESS OF THE TRACE

Discussion in 'Troubleshooting and Repair' started by quinoara, Jan 21, 2020.

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  1. quinoara

    quinoara

    4
    0
    Jan 21, 2020
    Dear Foristas, I am grateful in advance for some collaboration with this LEADER 4081 analog oscilloscope equal to the KENWOOD CS-5135. With failures with the brightness control, I have the service manual.

    Initially, when it was turned on, it took time to appear the stroke and when it appeared in 10 or 15 minutes, it did not let the brightness control.

    Initially, the operating voltages were checked, being all normal, note that when starting the ignition did not show high voltage, the high voltage section was checked and an isolated high-speed diode was found at one of the ends due to oxidation, in the Inten adjust circuit consisting of VR401, coming into operation correctly.

    The surprise came after armed and covered when a light was heard when a diode or resistance was broken, leaving the oscilloscope with excess brightness in the stroke and without intensity control this does not work.

    The X74-1490-00 card was checked thoroughly to see if something burst or burned I want to emphasize that no burning smell was felt, everything being in normal condition.

    Diode by diode, resistance by resistance, transistor by transistor, capacitors all manually with the ohmmeter were checked in detail, making different tests to verify the optimal state of each component, finding everything normal including the pot that controls the Focus intensity and astigmatism.

    The approach works normal and astigmatism control. It just does not control the brightness or intensity. Attached scheme and photo of the failure presented.

    I reiterate thanks for any suggestions.


    Apreciado Fred101 , estoy usando Traductor, pero entendi la respuesta .

    No subi el manual por que el servidor no lo permitió por que es muy grande.

    El VR401 control de inten adju está obrando en su derivación central de 75 a 140V, considerado normal.

    En cuanto a mi estimado Raff12 en esa sección se midió afuera del circuito cada una de las resistencias, diodos, condensadores de toda la etapa .

    Gracias a los dos por responder.
    Download link service manual https://we.tl/t-x3dRSxH1ET
     
  2. Tha fios agaibh

    Tha fios agaibh

    2,075
    686
    Aug 11, 2014
    Hola Quinoara,

    Have you checked Q405, Q407 and diodes in the vicinity of the intensity portion of the circuit? Are you using the diode check mode or just measuring in ohms?

    Screenshot_2020-01-22-11-12-37-1.png
     
  3. quinoara

    quinoara

    4
    0
    Jan 21, 2020
    Yes sir, they were taken out of the circuit, they were tested several times to check their status and they were exchanged for others, we think that the fault is possibly in the short CRT tube.

    These were the voltages taken with 10Meghomios probe, none presents changes when operating the intensity control and neither VR401. All negative voltajes. Unable to conclude anything
    K = -825V
    G1 = -703V
    P1 o G3 = -702V
     
  4. Tha fios agaibh

    Tha fios agaibh

    2,075
    686
    Aug 11, 2014
    Are you saying you accidentally shorted a trace or component somewhere?

    The voltages sound about right although g1 voltage should decrease with a higher intensity setting.

    Does the trace now appear within seconds of power up, as opposed to the 10 minute warm up problem?
     
  5. quinoara

    quinoara

    4
    0
    Jan 21, 2020
    No sir, nothing was accidentally cut, what I mean is that after solving the 10 minute warm-up failure, it was normal. The next day I went to turn it on and made a noise like when a capacitor or diode bursts. Running out of brightness control.
     
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