Reactive Overscanning

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I have a small Sony in the bedroom. When I watch, I usually do it with the  
closed captions on. i have no need for music on TV, plus you can hardly und
erstand the dialog, and some shit is just plain old annoying.  

It overscans. Part of the reason is a bad cap. If the circuit is what I thi
k it is, the cap filtering the B+ input to the flyback will increase horizo
ntal scan if the ESR goes high, and it also has intermittent immediate shut
down at startup. And it needs the 220 volt capo as well because it has jail
bars, but that doesn't affect the scanning.  

I think I got the caps laying around somewhere and intend to fix it. But I  
am sure the little shit will still overscan. It cuts off part of the captio
ns, which is the main problem. So I have a choice of two ways of reducing t
he horizontal size. I am just wondering which one is better.  

One way is to reduce the regulated B+. This might be easier ssaid than done
 if it is not adjustable and uses one of those hybrid DM type modules to co
ntrol the regulator. ButI would still do it with a staclk of Zeners and jus
t let the DM module be the current source. The regulation wouldn't be as ti
ght but it would be good enough. the drawbacks are that the drive to the ho
rixzontal poutput will be decreased which may result in higher dissipation.
 Also the B+ to the vertical IS being scan derived will be reduced and the  
on time of the bottom transistor may be longer and increase the dissipation
 of the IC. Adjusting the vertical height will not fix this. It would have  
to be adjusted anyway though because the ramp amp is probably run off a sub
-regulated supply. Otherwise I get that foldover at the top.  

The other alternative is a bucking winding on the flyback. Usually on these
 I can get in between the core and coil of the flyback so  
I just need to wind some wire in there which would be in the same polarity  
as the yoke feed, but inserted in series with the yoke return line. The pro
blem here is that it will decrease the high voltage and increase the deflec
tion sensitivity which would be working against itself. Also the switching  
optimization might be compromised with a longer duration pulse there, plus  
that lengthens retrace time which also works against itself.  

Just for shits and giggles which way you think would be better ? I'll get i
t done no matter, but I am just trolling for opinions. I got too much time  
on my hands I guess. I need some work.  

So, if you got too much time on your hands and know how these ^%&*##$s work
, type it up.

Re: Reactive Overscanning
On Friday, 9 February 2018 12:23:21 UTC, snipped-for-privacy@gmail.com  wrote:

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e closed captions on. i have no need for music on TV, plus you can hardly u
nderstand the dialog, and some shit is just plain old annoying.  
Quoted text here. Click to load it
hik it is, the cap filtering the B+ input to the flyback will increase hori
zontal scan if the ESR goes high, and it also has intermittent immediate sh
utdown at startup. And it needs the 220 volt capo as well because it has ja
ilbars, but that doesn't affect the scanning.  
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I am sure the little shit will still overscan. It cuts off part of the capt
ions, which is the main problem. So I have a choice of two ways of reducing
 the horizontal size. I am just wondering which one is better.  
Quoted text here. Click to load it
ne if it is not adjustable and uses one of those hybrid DM type modules to  
control the regulator. ButI would still do it with a staclk of Zeners and j
ust let the DM module be the current source. The regulation wouldn't be as  
tight but it would be good enough. the drawbacks are that the drive to the  
horixzontal poutput will be decreased which may result in higher dissipatio
n. Also the B+ to the vertical IS being scan derived will be reduced and th
e on time of the bottom transistor may be longer and increase the dissipati
on of the IC. Adjusting the vertical height will not fix this. It would hav
e to be adjusted anyway though because the ramp amp is probably run off a s
ub-regulated supply. Otherwise I get that foldover at the top.  
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se I can get in between the core and coil of the flyback so  
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y as the yoke feed, but inserted in series with the yoke return line. The p
roblem here is that it will decrease the high voltage and increase the defl
ection sensitivity which would be working against itself. Also the switchin
g optimization might be compromised with a longer duration pulse there, plu
s that lengthens retrace time which also works against itself.  
Quoted text here. Click to load it
 it done no matter, but I am just trolling for opinions. I got too much tim
e on my hands I guess. I need some work.  
Quoted text here. Click to load it
rk, type it up.

Reducing B+ reduces EHT too, which is derived from B+, so picture size does
n't change. But you get less brightness. Best option is make it work as it  
should.  

Don't increase B+ on failing tubes, it increases xray output.


NT

Re: Reactive Overscanning
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esn't change."

In my experience it does get smaller with less B+. Apparently the pulse to  
the yoke had a greater effect than the deflectiion sensitivity of the CRT.
  

Here's an interesting thing maybe. (because this is all academic, I'll get  
this one any which way once I get the thing on the bench)It was an NAP PTV  
310 I think, it was the one with the flyack on the power board on the right
 and the deflection board on the left, viewed from the rear.  

It used a regulation scheme somewhat like IRC a C3 chassis. The H drive com
es from the filter choke off the chopper regulator which is locked to the h
orizontal sync. This means the H output duty cycle increases with increased
 load on the PS. I guess it was a way to tighten up the H and HV regulation
.  

So this thing uses about the same circuit but there is a sub regulator for  
the B+ going only to the flyback. Looking at the circuit I could tell that  
the regulation was not rock solid, and I mean by design. Well one time I ha
d one that was shorted and since it only drops a few volts the set did not  
shutdown, or there was something not right in the shutdown circuit. But the
 B+ nto the flyback was rock solid then. This does NOT feed the yoke, that  
is a separate transformer and output all together on the other board.  

Well when the beam current increased, the raster size shrunk. +This must ha
ve had to do with the actual density of the electron beam. There could be n
o other reason. I saw the effect one other time only and thar was on a high
 ed Soy direct view moitor, I think a Profeel. It had separate hV and H as  
well. A few other models had it as well.  

But this NAP apparently they had to let the B+ and therefore the HV drop sl
ightly to keep the raster size constant. But so much for that.

This little shit is nothing like that, the only thing the same is the name.
 It is an elcheapo, model KV1396R and I am surprised it even has video in.  
That is good because the IF strip is whacked out and since my convertor box
 is defective and doesn't put out sound on video, only on RF, I have to use
 a VCR to tune it in. I'll probably fix that IF when I have it apart, but i
t works for now the way it is. The RF probably doesn't put out stereo so it
 picks off the mono signal before it becomes stereo in the box. I am NOT fi
xing the box. I refuse.  

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Don't worry.

1. I am old and I don't care if I glow in the dark.
2. The CRT is nice and strong.
3. Increasing B+ would not do what I want at all.

So I am safe.

Re: Reactive Overscanning
On Friday, February 9, 2018 at 7:23:21 AM UTC-5, snipped-for-privacy@gmail.com wrote:
Quoted text here. Click to load it
e closed captions on. i have no need for music on TV, plus you can hardly u
nderstand the dialog, and some shit is just plain old annoying.  
Quoted text here. Click to load it
hik it is, the cap filtering the B+ input to the flyback will increase hori
zontal scan if the ESR goes high, and it also has intermittent immediate sh
utdown at startup. And it needs the 220 volt capo as well because it has ja
ilbars, but that doesn't affect the scanning.  
Quoted text here. Click to load it
I am sure the little shit will still overscan. It cuts off part of the capt
ions, which is the main problem. So I have a choice of two ways of reducing
 the horizontal size. I am just wondering which one is better.  
Quoted text here. Click to load it
ne if it is not adjustable and uses one of those hybrid DM type modules to  
control the regulator. ButI would still do it with a staclk of Zeners and j
ust let the DM module be the current source. The regulation wouldn't be as  
tight but it would be good enough. the drawbacks are that the drive to the  
horixzontal poutput will be decreased which may result in higher dissipatio
n. Also the B+ to the vertical IS being scan derived will be reduced and th
e on time of the bottom transistor may be longer and increase the dissipati
on of the IC. Adjusting the vertical height will not fix this. It would hav
e to be adjusted anyway though because the ramp amp is probably run off a s
ub-regulated supply. Otherwise I get that foldover at the top.  
Quoted text here. Click to load it
se I can get in between the core and coil of the flyback so  
Quoted text here. Click to load it
y as the yoke feed, but inserted in series with the yoke return line. The p
roblem here is that it will decrease the high voltage and increase the defl
ection sensitivity which would be working against itself. Also the switchin
g optimization might be compromised with a longer duration pulse there, plu
s that lengthens retrace time which also works against itself.  
Quoted text here. Click to load it
 it done no matter, but I am just trolling for opinions. I got too much tim
e on my hands I guess. I need some work.  
Quoted text here. Click to load it
rk, type it up.


I wouldn't play with the B+, but maybe add a bit more capacitance across th
e HOT.  You'd lose a little HV admittedly, but on smallish CRTs that doesn'
t seem to be a problem IMO.

Re: Reactive Overscanning
On Friday, 9 February 2018 12:56:15 UTC, John-Del  wrote:
Quoted text here. Click to load it

the closed captions on. i have no need for music on TV, plus you can hardly
 understand the dialog, and some shit is just plain old annoying.  
Quoted text here. Click to load it
 thik it is, the cap filtering the B+ input to the flyback will increase ho
rizontal scan if the ESR goes high, and it also has intermittent immediate  
shutdown at startup. And it needs the 220 volt capo as well because it has  
jailbars, but that doesn't affect the scanning.  
Quoted text here. Click to load it
t I am sure the little shit will still overscan. It cuts off part of the ca
ptions, which is the main problem. So I have a choice of two ways of reduci
ng the horizontal size. I am just wondering which one is better.  
Quoted text here. Click to load it
done if it is not adjustable and uses one of those hybrid DM type modules t
o control the regulator. ButI would still do it with a staclk of Zeners and
 just let the DM module be the current source. The regulation wouldn't be a
s tight but it would be good enough. the drawbacks are that the drive to th
e horixzontal poutput will be decreased which may result in higher dissipat
ion. Also the B+ to the vertical IS being scan derived will be reduced and  
the on time of the bottom transistor may be longer and increase the dissipa
tion of the IC. Adjusting the vertical height will not fix this. It would h
ave to be adjusted anyway though because the ramp amp is probably run off a
 sub-regulated supply. Otherwise I get that foldover at the top.  
Quoted text here. Click to load it
hese I can get in between the core and coil of the flyback so  
Quoted text here. Click to load it
ity as the yoke feed, but inserted in series with the yoke return line. The
 problem here is that it will decrease the high voltage and increase the de
flection sensitivity which would be working against itself. Also the switch
ing optimization might be compromised with a longer duration pulse there, p
lus that lengthens retrace time which also works against itself.  
Quoted text here. Click to load it
et it done no matter, but I am just trolling for opinions. I got too much t
ime on my hands I guess. I need some work.  
Quoted text here. Click to load it
work, type it up.
Quoted text here. Click to load it
the HOT.  You'd lose a little HV admittedly, but on smallish CRTs that does
n't seem to be a problem IMO.

I'm not clear on the details of what you're suggesting, but anything that r
educes horiz scan power also reduces EHT, and vertical scan too if that run
s on a LOPT derived rail.


NT

Re: Reactive Overscanning
On Friday, February 9, 2018 at 9:37:41 AM UTC-5, snipped-for-privacy@gmail.com wrote:
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e:
Quoted text here. Click to load it
h the closed captions on. i have no need for music on TV, plus you can hard
ly understand the dialog, and some shit is just plain old annoying.  
Quoted text here. Click to load it
 I thik it is, the cap filtering the B+ input to the flyback will increase  
horizontal scan if the ESR goes high, and it also has intermittent immediat
e shutdown at startup. And it needs the 220 volt capo as well because it ha
s jailbars, but that doesn't affect the scanning.  
Quoted text here. Click to load it
But I am sure the little shit will still overscan. It cuts off part of the  
captions, which is the main problem. So I have a choice of two ways of redu
cing the horizontal size. I am just wondering which one is better.  
Quoted text here. Click to load it
n done if it is not adjustable and uses one of those hybrid DM type modules
 to control the regulator. ButI would still do it with a staclk of Zeners a
nd just let the DM module be the current source. The regulation wouldn't be
 as tight but it would be good enough. the drawbacks are that the drive to  
the horixzontal poutput will be decreased which may result in higher dissip
ation. Also the B+ to the vertical IS being scan derived will be reduced an
d the on time of the bottom transistor may be longer and increase the dissi
pation of the IC. Adjusting the vertical height will not fix this. It would
 have to be adjusted anyway though because the ramp amp is probably run off
 a sub-regulated supply. Otherwise I get that foldover at the top.  
Quoted text here. Click to load it
 these I can get in between the core and coil of the flyback so  
Quoted text here. Click to load it
arity as the yoke feed, but inserted in series with the yoke return line. T
he problem here is that it will decrease the high voltage and increase the  
deflection sensitivity which would be working against itself. Also the swit
ching optimization might be compromised with a longer duration pulse there,
 plus that lengthens retrace time which also works against itself.  
Quoted text here. Click to load it
 get it done no matter, but I am just trolling for opinions. I got too much
 time on my hands I guess. I need some work.  
Quoted text here. Click to load it
s work, type it up.
Quoted text here. Click to load it
s the HOT.  You'd lose a little HV admittedly, but on smallish CRTs that do
esn't seem to be a problem IMO.
Quoted text here. Click to load it
 reduces horiz scan power also reduces EHT, and vertical scan too if that r
uns on a LOPT derived rail.
Quoted text here. Click to load it

I'm assuming he's trying to reduce horizontal overscan as vertical overscan
 is always adjustable and he knows that.  Any modification to horiz width t
hat causes vertical height changes can be adjusted out.  By adding capacita
nce to the Horizontal Output Transistor (I believe you call it Line Output)
, the horizontal width will be affected.  The HV (EHT?) will change a bit b
ut it shouldn't be enough to cause issues.

Re: Reactive Overscanning
On Friday, 9 February 2018 16:31:37 UTC, John-Del  wrote:
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ote:
Quoted text here. Click to load it
ith the closed captions on. i have no need for music on TV, plus you can ha
rdly understand the dialog, and some shit is just plain old annoying.  
Quoted text here. Click to load it
at I thik it is, the cap filtering the B+ input to the flyback will increas
e horizontal scan if the ESR goes high, and it also has intermittent immedi
ate shutdown at startup. And it needs the 220 volt capo as well because it  
has jailbars, but that doesn't affect the scanning.  
Quoted text here. Click to load it
. But I am sure the little shit will still overscan. It cuts off part of th
e captions, which is the main problem. So I have a choice of two ways of re
ducing the horizontal size. I am just wondering which one is better.  
Quoted text here. Click to load it
han done if it is not adjustable and uses one of those hybrid DM type modul
es to control the regulator. ButI would still do it with a staclk of Zeners
 and just let the DM module be the current source. The regulation wouldn't  
be as tight but it would be good enough. the drawbacks are that the drive t
o the horixzontal poutput will be decreased which may result in higher diss
ipation. Also the B+ to the vertical IS being scan derived will be reduced  
and the on time of the bottom transistor may be longer and increase the dis
sipation of the IC. Adjusting the vertical height will not fix this. It wou
ld have to be adjusted anyway though because the ramp amp is probably run o
ff a sub-regulated supply. Otherwise I get that foldover at the top.  
Quoted text here. Click to load it
on these I can get in between the core and coil of the flyback so  
Quoted text here. Click to load it
olarity as the yoke feed, but inserted in series with the yoke return line.
 The problem here is that it will decrease the high voltage and increase th
e deflection sensitivity which would be working against itself. Also the sw
itching optimization might be compromised with a longer duration pulse ther
e, plus that lengthens retrace time which also works against itself.  
Quoted text here. Click to load it
ll get it done no matter, but I am just trolling for opinions. I got too mu
ch time on my hands I guess. I need some work.  
Quoted text here. Click to load it
#$s work, type it up.
Quoted text here. Click to load it
oss the HOT.  You'd lose a little HV admittedly, but on smallish CRTs that  
doesn't seem to be a problem IMO.
Quoted text here. Click to load it
at reduces horiz scan power also reduces EHT, and vertical scan too if that
 runs on a LOPT derived rail.
Quoted text here. Click to load it
an is always adjustable and he knows that.  Any modification to horiz width
 that causes vertical height changes can be adjusted out.  By adding capaci
tance to the Horizontal Output Transistor (I believe you call it Line Outpu
t), the horizontal width will be affected.  The HV (EHT?) will change a bit
 but it shouldn't be enough to cause issues.

It's only reasonable to assume he wants to tweak because he's out of adjust
ment.

But you're not understanding something. If you decrease the voltages out of
 the LOPTF by eg 10%, ie both scan voltage & EHT, the scan size remains exa
ctly the same. Think about why.


NT

Re: Reactive Overscanning
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stment. "

No, this is an elcheapo and there is no adjustment for H width at all. Ther
e is not even a pincushion circuit. If it was a matter of adjustment there  
would be no discussion.  

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f the LOPTF by eg 10%, ie both scan voltage & EHT, the scan size remains ex
actly the same. Think about why. "

That is simply not true on this type of unit. I have seen it 100s if times.
 When the regulator, which is a pass transistor, not switching, goes open t
he set runs on a ballast resistor that is there to decrease dissipation in  
the regulator transistor. In those cases the H width is small and the verti
cal has a distortion somewhat like a foldover at the top because it is not  
getting enough of a retrace boost. That is what that cap and diode do on th
e vertical IC. The supply is scan derived so it is also low when the main B
+ is low.  

I understand your reasoning, but in practice that is not how it is, the pic
ture shrink when the B+ drops. I can prove it, want pics ? (have to borrow  
a camera, lost it)

Re: Reactive Overscanning
On Friday, 9 February 2018 20:53:39 UTC, snipped-for-privacy@gmail.com  wrote:

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justment. "

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ere is not even a pincushion circuit. If it was a matter of adjustment ther
e would be no discussion.  
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 of the LOPTF by eg 10%, ie both scan voltage & EHT, the scan size remains  
exactly the same. Think about why. "
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s. When the regulator, which is a pass transistor, not switching, goes open
 the set runs on a ballast resistor that is there to decrease dissipation i
n the regulator transistor. In those cases the H width is small and the ver
tical has a distortion somewhat like a foldover at the top because it is no
t getting enough of a retrace boost. That is what that cap and diode do on  
the vertical IC. The supply is scan derived so it is also low when the main
 B+ is low.  
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icture shrink when the B+ drops. I can prove it, want pics ? (have to borro
w a camera, lost it)

There are 2 types of sets. Some will keep all picture geometry as B+ varies
, these don't have regulated supplies. Then there are sets that do need reg
ulation because it all goes pear shaped if B+ fluctuates. I didn't tell you
 which type you had.


NT

Re: Reactive Overscanning
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Those have pincusion ciruits with a feedback system that responds to the wi
dth and adjusts the pincusion output accordingly.  

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ed if B+ fluctuates."

Those do not compensate.

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I told you. The pincusion in this one is built into the CRT and there is no
 active circuitry. You can do this with a little 13". This set has regulati
on, a pass transistor with a ballast across  it. These are usually controll
ed by a small hybrid module but this one might be newer than that vintage.
  

There were some early GE sets that had automatic pincusion and no regulatio
n, and while the raster stayed straight, the size would vary directly with  
the AC line input. In these the H output ws a critical safety component bec
ause shutdown dependd on its faiiurre. Sometime in the late 1970s or early  
1980s sychg circuits were disapproved and they had to go to an active shutd
own circuit. The requirement, law whatever stated in no uncertain terms tha
t the HV protection cannot depend on the failure of a component. Some of th
e set built right after this mandate used four lead caps across the H outpu
t because its failure was the chief cause of excessive HV.

Re: Reactive Overscanning
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call it Line Output), the horizontal width will be affected.  The HV (EHT?)
 will change a bit but it shouldn't be enough to cause issues. "

Adding capacitance across the primary (or any winding) of the flyback will  
decrease the HV, which I don't care. I watch at night and could turn it dow
n. I only got it set bright so it doesn't shut down after startup. Adding t
hat capacitance also will lengthen retrace time which would make the APPARE
NT overscan worse. I mean, with the increased retrace time it would SEEM to
 overscan more.  


Re: Reactive Overscanning
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 scan too if that runs on a LOPT derived rail"

True, but it does not stay linear. The vertical in this vintage of sets is  
like an amp that simply compares the current output with a ramp waveform. F
requently, the ramp waveform stays the same amplitude because it is further
 regulated, which then overdrives the vertical because the B+ to it is low.
 They cut it pretty close to keep the dissipation down. A smaller heat sink
 is cheaper. And most of these ICs are in a family, like LA 7830, 7831, 783
2, 7833 with the highest number having the best max ratings. I would always
 replace them with the highest rated one in the family since they are other
wise identical and with a quantity price break the better part may actually
 cost less, but on a manufacturing level it pays to custom choose only as m
uch as you need because on a million units a small saving adds up. Possibly
 to a bonus for someone.  


Reactive Overscanning
I once slightly reduced the horizontal size inserting a small inductor in series with the yoke.

Re: Reactive Overscanning
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 series with the yoke. "

That method affect the linearity. Sometimes it is acceptable and other time
s it is not.The only way is with a bucking winding. Sometimes you can find  
a trace positive winding on the flyback feeding a scan derived source but t
his is a direct line set, no power transformer. Hot chassis. That means it  
would cross cold and hot grounds and that is a big nono. Finding the right  
coil might be a problem as well, but with a tertiary winding on the flyback
 you can add or subtract turns to get it right where you want it.  

Note that this also lengthens retrace time but not as much as adding capaci
tance across the primary.

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