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Philips 41JP20 still shuts down

Discussion in 'Electronic Repair' started by James Sweet, Jul 11, 2004.

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  1. James Sweet

    James Sweet Guest

    I messed with this thing some more and am still stuck. Press the power
    button and the green light comes on, HV comes up, about a second later the
    relay clicks and the PSU shuts down. Power light remains on and the other
    two LED's illuminate. Remote (which I think was working before) doesn't turn
    the set on or off.

    So far I've:

    Replaced arcing flyback, that got the set up and running briefly but I
    turned it off to reassemble and then it started this shutdown thing

    Resoldered entire power board

    Resoldered most of the sweep board

    Resoldered yoke interconnect board

    Checked all the diodes, transistors, and fusible resistors on both the power
    board and sweep board

    Measured voltages out of the power supply including HV, all appear within
    spec for the ~1 sec it'll stay powered on

    Grumbled, cursed at it and brooded


    I'm wondering if I should just hope to find a known good chassis for it?
    Someone told me it's a PTV300.
     
  2. techforce

    techforce Guest

    I was told the ABL Pin on the FBT can trigget Shutdown in a TV or Monitor.
    Does this set have an ABL Pin and related Circuitry? Sometimes there a TRIP
    Pot to set.


    | I messed with this thing some more and am still stuck. Press the power
    | button and the green light comes on, HV comes up, about a second later the
    | relay clicks and the PSU shuts down. Power light remains on and the other
    | two LED's illuminate. Remote (which I think was working before) doesn't
    turn
    | the set on or off.
    |
    | So far I've:
    |
    | Replaced arcing flyback, that got the set up and running briefly but I
    | turned it off to reassemble and then it started this shutdown thing
    |
    | Resoldered entire power board
    |
    | Resoldered most of the sweep board
    |
    | Resoldered yoke interconnect board
    |
    | Checked all the diodes, transistors, and fusible resistors on both the
    power
    | board and sweep board
    |
    | Measured voltages out of the power supply including HV, all appear within
    | spec for the ~1 sec it'll stay powered on
    |
    | Grumbled, cursed at it and brooded
    |
    |
    | I'm wondering if I should just hope to find a known good chassis for it?
    | Someone told me it's a PTV300.
    |
    |
    |
     
  3. Ol' Duffer

    Ol' Duffer Guest

    PTV330 to be exact, but the distinction amounts to frills like high
    power stereo sound that are almost surely unrelated to your problem.
    Used to see these all the time, not so much anymore. 'Bout 15 years
    old y'know. So okay, I have a little free time and I'll try to help.

    Grounds:
    I'll assume you've found your hot ground and cold ground test points
    on the power board (the one with the flyback). If not;
    TP1 = cold ground
    TP3 = hot ground

    Main Power Supplies:
    Verify 130V (hot) supply at TP7/TP3, also on collector of Q14,
    not very critical at this point, anything within a few volts will
    probably work.
    Verify approximately 120V (hot) on Q14 output, easier to clip onto
    R69 the big power resistor standing up. Actual voltage will vary,
    I usually see about 118V on working sets.
    If the above measurements are true, the regulator is working and
    you have a horizontal drive signal.

    HV Reference:
    Now check the +210 (cold) EHT reference TP14/TP1. I expect to see
    about 180V here on a properly working set, and that is what I use
    as my initial target if I have to re-adjust. If this looks high,
    it may be the cause of your shutdown. Here's the deal, high voltage
    is regulated by feedback from a tertiary winding on the hot side
    TP15/TP3, but over-voltage is detected by a different tertiary
    winding on the cold side TP14/TP1, so replacing the flyback changes
    this relationship and often causes unnecessarily touchy shutdown.
    They were sometimes overly touchy from the factory anyway. The
    over-voltage detection circuit is on the other (deflection) board,
    but since your main failure appears to have been the flyback, you
    may not have to mess with the other board.

    If you determine that the HV regulator needs to be turned down,
    locate RP2. It's under one of the metal cans that look like IF
    transformers, but have no holes. The cans are installed by the
    factory to prevent anyone from messing with their adjustments.
    These parts of the schematic (including the flyback) are marked
    "non-serviceable area". I like to leave the can off so that the
    next guy (who may or may not be me) will know the pot has been
    tweaked.

    Seems like a good place to pause for questions, or may be all
    you need to know. If not, post some more and I can try to walk
    you through the shutdown circuits.
     
  4. James Sweet

    James Sweet Guest


    So after the chaos of moving settled down I was *finally* able to get to
    this. Removing the cans which I had assumed were transformers I found the
    adjustment pots and discovered that turning down the HV does indeed fix the
    shutdown, it's still quite touchy though. Before I dig too deep, what should
    the HV be on a properly running set? Or should I just measure the HV
    reference? There doesn't appear to be an adjustment for the shutdown as many
    sets have, what modification do I need to make to make it less sensitive?
    I'm assuming a resistor change but not having a schematic makes it
    difficult.

    Once this is all done I get to experience the joys of a full calibration, I
    dread doing the convergence on PTV's, still amazes me they can have them
    looking so good from the factory.
     
  5. Ol' Duffer

    Ol' Duffer Guest

    The service manual doesn't say what the actual HV is
    supposed to be, but it's "real high" (40KV+?) and they
    (deliberately?) don't provide a place where you can
    measure it. And I seriously don't recommend trying to
    poke through insulation anywhere to get at it.

    I go by the EHT reference on TP14 (cold), and expect
    to see about 180VDC. Again, the factory doesn't give
    an exact number or a procedure, this is just what I
    have seen on normally behaving sets.

    Their approach was "module replacement" when they built
    these, and they witheld a lot of information about what
    were essentially easily-repaired boards.
    It's on the other board (deflection). Look for RP1 under
    another one of those cans. The EHT reference is dropped
    through R39, then RP1, then R40 to ground. The wiper of
    RP1 goes through a Zener diode Z3 to the base of Q3, which
    is the over-voltage sensor. Z3 has been known to become
    leaky, and the factory tech didn't tell me it was a 6.2V
    1/2W (wink). If you're sure the HV isn't out of control,
    you can short the base of Q3 to ground and run the HV up
    and down to eliminate other stuff.

    There are some other things that can cause shutdown, but
    this is the most common area for "touchy".
    Is your hotmail address valid (wink)?
    Fortunately, the controls pretty much do what they say.
    If they haven't been messed with, it may not need much.
     
  6. James Sweet

    James Sweet Guest

    Thanks a bunch for all the info, this should be all I need to have this
    thing finished. I'm quite sure the convergence and color ballance will need
    a full going over as I had all three CRT's out to change the coolant just a
    couple weeks before the flyback burned up. Fortunatly I have the sheet that
    details the setup procedure and I have a video CD I made with some basic
    test patterns (a shame they don't even provide a built in crosshatch
    generator like some older PTV's I've dealt with) so I think with some
    patience it should be looking pretty good.

    It sat dead for several years before it was given to me and I had it for
    almost 3 years before I had a chance to repair the power supply so the CRT's
    themselves are in remarkably good condition for the age. Seems once I
    brought it back to life just about everything else that can go wrong with it
    did.
     
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