TV osiliscope

Discussion in 'General Electronics Chat' started by electronis whiz, Oct 1, 2013.

  1. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    I got an old CRT TV the other day somebody gave me. I saw something online about cutting the HV horizontal coil, and moving the vertical opt to the horizontal coil. Then using vertical coil and hooking an amp up to it and applying input to amp. I tried using an external amp connected to radio, but all I ever get is a dot in the center. what I understand there should be a line. They adjusted something to do with the scanning frequency I'm thinking maybe that is the issue, but i'm not seeing this on mine.
    Mine has the following internal adjustments on the main board:
    vlt-adj, h-con, RF-AGC, V-size, sub-bri, V center.
    I don't really have much idea what any of them do. I looked online, but hard to find anything about crt repair now. From sounds of it I would guess either be RF-AGC, or sub-bri, but mine may not have this either. The rest i'm thinking are for size, positioning.
    they used an analog style tuner/volume unit, mines digital control. not sure makes a difference, but I wouldn't think since mine makes blue screen if no signal so should work.

    The instructions i'm using are:
  2. MrChips


    Oct 2, 2009
    The amount of current required to deflect the beam magnetically is very large.
    You need high power amps for it to work.

    Secondly, the maximum frequency is relatively low. Consider that the horizontal scan frequency is 15.750kHz.

    You will not be able to view any signal much greater than 20kHz.
  3. electronis whiz

    Thread Starter Well-Known Member

    Jul 29, 2010
    The instructions mentioned it didn't have much of a range basically human hearing range. I hooked radio into 50 watt power booster had radio about level 5 level 1 is about normal listening on this one. Not sure what it will take to make an amp to drive this. I can try what he did I guess with his amp. I would think could just use a good size transistor and put base on source of signal and emitter/drain on like 12V DC supply.
  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
    more info here

    The tv uses the line oscillator to drive the beam across the screen left to right, it also uses the oscillator to generate the EHT of 20 to 30Kv for the tube anode ( rubber cap on back side of tv tube) from the LOPT, so disconneting it will kill the voltage and the screen wont be visible.
    Last edited: Oct 2, 2013
  5. Jaguarjoe

    Active Member

    Apr 7, 2010
    If you are driving the vertical section of the yoke, why not use the vertical output circuit that's already there?

    If you can find old electronic mags from ~65 years ago, lots of these will pop up.