Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

So, if you got too much time on your hands and know how these ^%&*##$s work, type it up.
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On Friday, 9 February 2018 12:23:21 UTC, wrote:

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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

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


Reducing B+ reduces EHT too, which is derived from B+, so picture size doesn'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
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On Friday, February 9, 2018 at 7:23:21 AM UTC-5, wrote:
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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

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



I wouldn't play with the B+, but maybe add a bit more capacitance across the HOT. You'd lose a little HV admittedly, but on smallish CRTs that doesn't seem to be a problem IMO.
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On Friday, 9 February 2018 12:56:15 UTC, John-Del wrote:
On Friday, February 9, 2018 at 7:23:21 AM UTC-5, wrote:


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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

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



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


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


NT
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On Friday, February 9, 2018 at 9:37:41 AM UTC-5, wrote:
On Friday, 9 February 2018 12:56:15 UTC, John-Del wrote:
On Friday, February 9, 2018 at 7:23:21 AM UTC-5, wrote:


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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

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



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


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


NT


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 that causes vertical height changes can be adjusted out. By adding capacitance 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 but it shouldn't be enough to cause issues.


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On Friday, 9 February 2018 16:31:37 UTC, John-Del wrote:
On Friday, February 9, 2018 at 9:37:41 AM UTC-5, tabby wrote:
On Friday, 9 February 2018 12:56:15 UTC, John-Del wrote:
On Friday, February 9, 2018 at 7:23:21 AM UTC-5, wrote:


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 understand the dialog, and some **** is just plain old annoying.

It overscans. Part of the reason is a bad cap. If the circuit is what 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 immediate shutdown at startup. And it needs the 220 volt capo as well because it has jailbars, 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 **** will still overscan. It cuts off part of the captions, 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.

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 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 to the horixzontal 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 problem here is that it will decrease the high voltage and increase the deflection 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 ****s and giggles which way you think would be better ? I'll 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.

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


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


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


NT


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 that causes vertical height changes can be adjusted out. By adding capacitance 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 but it shouldn't be enough to cause issues.


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

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 exactly the same. Think about why.


NT
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"Reducing B+ reduces EHT too, which is derived from B+, so picture size doesn'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 comes from the filter choke off the chopper regulator which is locked to the horizontal 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 had 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 have had to do with the actual density of the electron beam. There could be no 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 slightly to keep the raster size constant. But so much for that.

This little **** 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 it 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 fixing the box. I refuse.

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


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.
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"By adding capacitance 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 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 down. I only got it set bright so it doesn't shut down after startup. Adding that capacitance also will lengthen retrace time which would make the APPARENT overscan worse. I mean, with the increased retrace time it would SEEM to overscan more.

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"It's only reasonable to assume he wants to tweak because he's out of adjustment. "

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

"ut 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 exactly 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 the 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 vertical 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 the 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 picture shrink when the B+ drops. I can prove it, want pics ? (have to borrow a camera, lost it)
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"but anything that reduces horiz scan power also reduces EHT, and vertical 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. Frequently, 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, 7832, 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 otherwise 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 much as you need because on a million units a small saving adds up. Possibly to a bonus for someone.



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On Friday, 9 February 2018 20:53:39 UTC, wrote:

"It's only reasonable to assume he wants to tweak because he's out of adjustment. "


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

"ut 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 exactly 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 the 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 vertical 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 the 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 picture shrink when the B+ drops. I can prove it, want pics ? (have to borrow 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 regulation because it all goes pear shaped if B+ fluctuates. I didn't tell you which type you had.


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I once slightly reduced the horizontal size inserting a small inductor in series with the yoke.
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"Some will keep all picture geometry as B+ varies,"

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

"Then there are sets that do need regulation because it all goes pear shaped if B+ fluctuates."


Those do not compensate.

"I didn't tell you which type you had. "


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 regulation, a pass transistor with a ballast across it. These are usually controlled 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 regulation, 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 because 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 shutdown circuit. The requirement, law whatever stated in no uncertain terms that the HV protection cannot depend on the failure of a component. Some of the set built right after this mandate used four lead caps across the H output because its failure was the chief cause of excessive HV.
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"I once slightly reduced the horizontal size inserting a small inductor in series with the yoke. "

That method affect the linearity. Sometimes it is acceptable and other times 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 this 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 capacitance across the primary.
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