Oscilloscope on crt monitor repair

Discussion in 'General Electronics Chat' started by Kenny, Aug 20, 2010.

  1. Kenny

    Thread Starter AAC Fanatic!

    Oct 11, 2004
    I have a dead 17" crt monitor and I want to fix it by using the oscilloscope.
    The problem seems to be in the low voltage power supply, then I want to check the signals on it, but I have a big doubt:
    ¿Where I must to connect the ground clip?
    Of course ground. But in the low voltage power supply (before T901) the ground is not the same oscilloscope ground (earth).

    I have read the threads about grounding and I understand them, but how is the way?

    I want to try connecting the monitor with a prong without earth connection and the scope ground clip to the negative leg of the main capacitor.
    But this is the first time that I'm using a scope to debug a monitor, and I want to know how is the WAY?

    I want to see the waveforms that are showed on monitor schematics.

    Thanks in advance!
  2. tom66

    Senior Member

    May 9, 2009
    I would be careful with my oscilloscope and a CRT, there are voltages in there (such as the focus voltage and EHT voltage) which can easily exceed the 250V or 400V rating of the oscilloscope.

    When I am testing equipment, I usually ground the probe to part of the exposed metal case. This has never failed me, but perhaps someone else has a different opinion.
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
    Unless you're 100% sure the monitor has a fully isolated power supply DO NOT hook a scope or any other non battery operated test equipment to it. That was always a first rule when working on consumer electronics, especially televisions.