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Nexxtech TV picture doesn't fill the screen

Discussion in 'Electronic Repair' started by Rick, Nov 15, 2013.

  1. Rick

    Rick Guest

    I have a B&W 5" CTR Nexxtech TV, model 1612002 (used as a lobby monitor),
    which when switched on, only displays the top half of the picture normally,
    while the bottom half is squashed into a narrow bright horizontal band.

    You can sort of make out that the rest (bottom) of the picture is upside
    down. After it's been on for a while, the bottom half starts to extend
    further down, and becomes right side up, but is still squashed, so a 1/4
    of the screen remains blank. Other than the brightness and V-hold, there
    are no other adjustments inside or outside.

    Does anyone have any ideas where to look for the reason for this? I have an
    electrical background (not with TVs though), so replacing parts would not be
    a problem. Any hints would be appreciated. -Rick
     
  2. Guest

    You almost certainly have a dried out capacitor in the vertical deflection amplifier. Just a guess but I bet it's 1000 to 2200 uF very near the vertical amp. This happens all the time with Sony CRT monitors.

     
  3. Phil Allison

    Phil Allison Guest


    ** No one familiar with electronics calls what they do "electrical".

    So what is your "background" actually in ?

    What if any test gear do you have ?

    Access to any components like ICs and electros that might be found in a
    CRT TV set ?



    .... Phil
     
  4. Rick

    Rick Guest

    Thanks, G², greatly appreciated!
     
  5. Rick

    Rick Guest

    Ok I'll bite. "No one" wouldn't neccessarily include those where
    English is their second language.
    My "background" is an electromechanical Journeyman / Apprenticeship
    - not sure what the English equivalent is.
    I have owned a variety of test gear, including a scope.

    I have fixed or *modified* dozens of VCRs (Beta, SVHS, Hi8), the odd
    TV, lots of communication-types of radios, and done some minor surface
    component work.

    Time is valuable -- particularly when TVs are not your specialty,
    so just trying to get some ideas from those who deal with that sort of
    thing on a regular basis.

    No offence taken though, Phil, you provide a lot of valuable input
    otherwise.
     
  6. Ken Layton

    Ken Layton Guest

    My experience with CRT type tv's and monitors over the past 40 years has been about 75% of the time bad electrolytic capacitors have been the cause ofproblems. The other 25% of the time it has been solid state components like transistors, IC's, diodes, etc causing troubles.

    In your case I think the first place to look is at any electrolytic capacitors in the vertical deflection stage. There might be an obvious bad one with a bulged/blown out top or leaking out the bottom of it. Naturally, a capacitor meter would be a big help in testing the capacitors and finding an electrically bad one.

    The vertical output stage may either have a pair of transistors (one operates the top half of the picture and the other operates the bottom half) running it or it could have the vertical output stage combined in a single integrated circuit which is usually bolted to a heat sink to keep it cool.
     
  7. Ken Layton

    Ken Layton Guest

    Forgot to mention, likely capacitors causing your problem could be ones either rated at 1000 to 2200 uf (around 10 to 25 volts) or look for any that are rated at a small uf like 3.3 uf but at higher voltage like say for instance 160 volts.

    I had one of those Harbor Freight 5" B&W security camera monitors with a "no vertical deflection" symptom and it turned out to have two bad electrolytic capacitors: a 2200 uf @ 10 volts and a 3.3 uf @ 160 volts. Replacing them restored the monitor back to full operation again.
     
  8. Phil Allison

    Phil Allison Guest

    "Rick"

    ** Yes it would.
    ** Electrical technician.

    ** Past tense ?
    ** Mechanical work - right ?

    ** CRT sets are past tense - nobody fixes them.
    ** Others have posted the only advice possible.

    Did you really think someone here KNEW that obscure TV ?


    .... Phil
     
  9. My experience - boost capacitor, often about 100uF at 35 volts, near the
    vertical output IC.

    Mark Z.
     
  10. John-Del

    John-Del Guest

    If this happened suddenly (one minute full deflection, the next half pix), it's most likely not a capacitor, at least not the only problem.

    If it uses an IC for vertical deflection, it it most likely bad or can evenhave cracked solder along the pins. Try defluxing the pins thoroughly, then resolder with quality solder. If it runs OK, leave as is. Cracked solder is a function of age, heat, and vibration.

    If the IC or discrete output transistors is\are bad, replace it and ESR every electrolytic in the circuit. A high ESR cap may not cause any initial symptom, but the IC will fail.
     
  11. Guest

    Actually, not in my experience. The boost cap or circuit only speeds up theretrace. What the OP described sounds like high ESR in the main output cap, if the unit has one. Because of the inductance of the yoke winding, high ESR acting like a resistor will cause the top of the raster to be still kinda stretched, but the bottom will be compressed because that is the part where it needs the low frequency component of the waveform. The boost cap only causes problems at the top usually.

    I think the problem is going to be a large cap, like a 2,200 uF or so.
     
  12. Guest

    "If this happened suddenly (..."

    Good point. We do not know if the guy just got the thing or what. Almost any problem with the caps comes on gradually. It is quite rare that one goes all the sudden. If it does it is usually completely open or shorted, in either case there would probably be no deflection at all.

    Actually a model number might help. I got two databases (paid) with a wholebunch of symcures. A print would be great. The thing might not even have an output coupling cap, which would mean the problem is likely the bottom output. (in IC or not)

    On the other hand, the ramp cap associated with the vertical driver can also do that. Sometimes those are tantalum and they can fail just like that onoccasion.
     
  13. Rick

    Rick Guest

    Turned out to be a FEC 2200uF / 10V capacitor with no
    obvious signs of bulging or leaking. Took only a couple of
    minutes to fix, and works great again now!

    Thanks G² and everyone else for their input !!
     
  14. Ken Layton

    Ken Layton Guest

    Glad to hear you got it fixed. :)
     
  15. Guest

    Yes. Now the argument can start. We can talk about whether it was the Christian Fundamentalists or the JEws who are at fault, or if there is no fault because the thing is 100 years old. Then we can go into the Prussian governemnt's involvment in the current middle east crisis.

    But let's not forget about the Russians and their hand in not stopping the tragedy of 9/11 which killed almost as many people as hospitals and drunk drivers combined in a month.

    Then there are those socio-economic factors that make most of us not give afuck anymore.

    Or we can start picking on Phil Allison. Your call.
     
  16. Ken Layton

    Ken Layton Guest

    The OP did post the model number in the original post: Nexxtech model 1612002.
     
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