Nexxtech TV picture doesn't fill the screen

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

Reply to
Rick
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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 vertic al amp. This happens all the time with Sony CRT monitors.

Reply to
stratus46

"Rick"

** 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

Reply to
Phil Allison

Thanks, G², greatly appreciated!

Reply to
Rick

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.

Reply to
Rick

Check the vertical deflection driver if new caps (use good quality 105C ones of course!) don't fix the problem.

Use low ESR caps for anything on the horizontal circuit, check the other

electrolytic caps using an ESR meter like the blue Bob Robert ESR meter kit one that we sell.

We've also replaced a lot of the associated deflection transistors in vertical circuits when the cap failed...

John :-#)#

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Reply to
John Robertson

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

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

The vertical output stage may either have a pair of transistors (one operat es the top half of the picture and the other operates the bottom half) runn ing it or it could have the vertical output stage combined in a single inte grated circuit which is usually bolted to a heat sink to keep it cool.

Reply to
Ken Layton

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

I had one of those Harbor Freight 5" B&W security camera monitors with a "n o vertical deflection" symptom and it turned out to have two bad electrolyt ic capacitors: a 2200 uf @ 10 volts and a 3.3 uf @ 160 volts. Replacing the m restored the monitor back to full operation again.

Reply to
Ken Layton

"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

Reply to
Phil Allison

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

Mark Z.

Reply to
Mark Zacharias

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 even have cracked solder along the pins. Try defluxing the pins thoroughly, th en resolder with quality solder. If it runs OK, leave as is. Cracked sold er is a function of age, heat, and vibration.

If the IC or discrete output transistors is\are bad, replace it and ESR eve ry electrolytic in the circuit. A high ESR cap may not cause any initial s ymptom, but the IC will fail.

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Reply to
John-Del

vertical output IC. Mark Z.

Actually, not in my experience. The boost cap or circuit only speeds up the retrace. 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 kin da stretched, but the bottom will be compressed because that is the part wh ere it needs the low frequency component of the waveform. The boost cap onl y causes problems at the top usually.

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

Reply to
jurb6006

Good point. We do not know if the guy just got the thing or what. Almost an y 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 eit her case there would probably be no deflection at all.

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

On the other hand, the ramp cap associated with the vertical driver can als o do that. Sometimes those are tantalum and they can fail just like that on occasion.

Reply to
jurb6006

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 !!

Reply to
Rick

Glad to hear you got it fixed. :)

Reply to
Ken Layton

Yes. Now the argument can start. We can talk about whether it was the Chris tian 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 govern emnt'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 d rivers combined in a month.

Then there are those socio-economic factors that make most of us not give a f*ck anymore.

Or we can start picking on Phil Allison. Your call.

Reply to
jurb6006

any problem with the caps comes on gradually. It is quite rare that one goe s all the sudden. If it does it is usually completely open or shorted, in e ither case there would probably be no deflection at all.

le bunch 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)

lso do that. Sometimes those are tantalum and they can fail just like that on occasion.

The OP did post the model number in the original post: Nexxtech model 16120

02.
Reply to
Ken Layton

YAWN

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Reply to
Michael A. Terrell

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