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CTC169 36" dead

Discussion in 'Electronic Repair' started by Mike, Jan 27, 2007.

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  1. Mike

    Mike Guest

    Got this set, it would turn on and fire HV for a second, then shut back
    down. it wont do it anymore, only did it one time.


    I monitored C4118 while pressing the button, it would start off at 13.1
    volts, and drop down to about 5 volts. when power button was pressed.


    I then replaced CR4118, and replaced 2 caps in the IC chip of the power
    supply. the main B+ at standby levels is about 143vdc. the 15v standby is
    about 13.3 still.


    but this time, when you press the power button, OR perform the manual
    power-on, bypassing the micro unit, the voltage doesnt drop anymore, but the
    set still is dead. HOT is fine, chopper is running. I dont know what to look
    for next.

    however if i hold the board in manual power on, every once in awhile the
    degauss relay would start clicking on and off a little bit, very faintly,
    like a weak supply somewhere.

    any ideas?
     
  2. Ken Weitzel

    Ken Weitzel Guest

    Hi...

    Take a look at the 15v supply, if there's a fair bit of ac ripple there,
    go ahead and change c4145.

    Take care.

    Ken
     
  3. Mike

    Mike Guest

    i used an ESR meter. the cap has very good ESR, i shoudl change it though.
    but nothing makes since. the 13.3v is solid, even when you press power
    button, unlike before. i thought its supposed to raise when power pressed,
    it doesnt.
     
  4. Mike

    Mike Guest

    im going to scope it and be sure. good point. ;-)
     
  5. Mike

    Mike Guest

    i think something somewhere is funky. I scoped out the 15v standby, it looks
    like sawtooth, with a ringing on the up-ramps.


    when i press power, you can here the supply "tick" and the sawtooth gets
    considerably larger, and then drops back down the way it does. the cycle
    repeats each time i hit power.

    i scoped the 26v source from the power supply, it also has this "sawtooth"
    ripple, but its considerably smaller. although still preseant.


    any ideas?
     
  6. Meat Plow

    Meat Plow Guest

    High ESR caps
     
  7. Mike

    Mike Guest

    i replaced the cap off of the 15V standby, and i still get the same shit. im
    at a standstill im assuming somethign is loading the standby down, shorted
    somewhere.


    as the set only fired up once wiht HV. and never did it again.

    the HOT tests fine.
     
  8. Mike

    Mike Guest

    i think its the horiz circuit.


    When i press power, pin26 of U1001 jumps to about 8.6 volts. holds it for
    about 3 to 5 seconds, and drops back down. jumps back up each time i press
    power.

    there is NO drive on the HOT. on any attempt. even on plugin. no drive.
    somethings up.
     
  9. Ken Weitzel

    Ken Weitzel Guest

    Weird.... the 26 volts you mentioned was present in a previous message
    is derived from horizontal scan... ???

    Ken
     
  10. Mike

    Mike Guest

    no. from the chopper.
     
  11. Mike

    Mike Guest

    i have nothing from the horiz circuit. the horiz circuit has failed.

    i think U1001 is bad.

    i removed the horiz drive xistor. when power is pressed, NO waveform on the
    base of the transistor. im looking for a strong saw or square wave i assume.
    well i have nothing but a little bit of noise when the power is pressed. and
    i have to crank the scope up to see it.

    now if i scope out pin 23, the H-drive out. i have the same type of noise,
    but a little bit bigger in amplitude.

    shouldnt i have a strong defined square pulse? at 15.25khz. well i get a
    faint bit of noise. almost like a ring type of noise.


    when power is pressed, the 9v VCC to the hoiz osc of U1001 goes present. so
    whats left. U1001?
     
  12. Ken Weitzel

    Ken Weitzel Guest

    Hi...

    What's the voltage on pin 16 u4101? (power on, let it run for a few
    seconds while you watch - wandering around?)

    Take care.

    Ken
     
  13. Mike

    Mike Guest

    no. stays a solid 51.6vdc
     
  14. Mike

    Mike Guest

    i moved my ground probe to the negative side of the primary, i had it on the
    negative side of the secondary, this time i get a rock solid 10.2v
     
  15. Ken Weitzel

    Ken Weitzel Guest

    Right where it should be; indicates that the set "isn't turning on" as
    opposed to being held off by its own protection circuits.

    My address is good; send me an email from an address that can take a
    few megs of attachment. And if necessary, do whatever you have to so
    that attachments from me are acceptable

    Take care.

    Ken
     
  16. Mike

    Mike Guest

    ok.

    maybe a picture is worth a thousand words.


    here is the scoped output of the 15v standby. also the same waveform is
    present on all the outpus of the power supply. the waveform gets a little
    bit larger when the power button is pressed.

    http://pubserver1.ath.cx/scope.jpg

    Also, you see the ringing on the peaks? well when i scope the output of the
    U1001 to the driver transistor, i get a flat line, with the same exact
    ringing. but no square output. horiz VCC goes to 9v when power is pressed,
    and drops back to 0v approximately 3 to 4 seconds later.

    im not sure what the issue is. looks liek something is seriosuly loading the
    supply. but im not sure. all 4 caps in the primary have been replaced, and
    the cap on the 15v CR4118 was replaced, along wiht CR4118.
     
  17. Mike

    Mike Guest

    im assuming the "ringing" is the power supply turning on to charge up the
    caps to get the voltage back to what it shoudl be, and the steady decline is
    the caps discharging, then hits the threshold, and supply starts again.
     
  18. Mike

    Mike Guest

    for the hell of it, i disconnected the amplifier board completely from the
    circuit, all plugs, and unsoldered the entire board.


    the ramp pulse with ringing is still present on the power supply.

    but now, when i scope U1001, when i press power, my pulse is showing up now.
    it wasnt before. wtf...
     
  19. Mike

    Mike Guest

    nevermind, i spoke too soon. its gone again :-(

    im guessing either the ramp noise from the output of the supply is
    disturbing the IC, or U1001 is intermittantly defective. :-\
     
  20. Mike

    Mike Guest

    it was audio out board. i plugged the horiz driver xistor back in. its not
    dead anymore. although somtiems it turns on now. sometimes it doesnt. but if
    i plug the audio board back up. it wont work at all.
     
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