Reactive Overscanning

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.

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.

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.

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.

se I can get in between the core and coil of the flyback so

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.

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.

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

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.

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.

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.

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.

se I can get in between the core and coil of the flyback so

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.

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.

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.

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.

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.

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.

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.

hese I can get in between the core and coil of the flyback so

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.

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.

work, type it up.

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

e:

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.

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.

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.

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.

these I can get in between the core and coil of the flyback so

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.

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.

s work, type it up.

s the HOT. You'd lose a little HV admittedly, but on smallish CRTs that do esn't seem to be a problem IMO.

reduces horiz scan power also reduces EHT, and vertical scan too if that r uns on a LOPT derived rail.

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.

ote:

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.

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.

. 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.

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.

on these I can get in between the core and coil of the flyback so

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.

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.

#$s work, type it up.

oss the HOT. You'd lose a little HV admittedly, but on smallish CRTs that doesn't seem to be a problem IMO.

at reduces horiz scan power also reduces EHT, and vertical scan too if that runs on a LOPT derived rail.

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

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.

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.

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.

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.

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)

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.

justment. "

ere is not even a pincushion circuit. If it was a matter of adjustment ther e would be no discussion.

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

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.

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

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

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

ed if B+ fluctuates."

Those do not compensate.

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.

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.