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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 13, 2016 1:09 pm Post subject: |
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Might be an idea to use a scope to see what is happening there?
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the dude
Joined: 11 Sep 2013
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| Posted: Sat Feb 13, 2016 1:16 pm Post subject: |
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| Quote: | | So the retrace lines should be very bright |
OK, -9 at the input of the OPA means +8 at the output. This voltage gets inverted again by the 2. stage. That means FULL cut off. The ABL loop thinks "Oh, no beam. Must turn G2 high". Notice that the negative rail is -2V while the positive is +8V, so -2V ist the max. negative voltage that the op amps can provide.
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the dude
Joined: 11 Sep 2013
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| Posted: Sat Feb 13, 2016 1:17 pm Post subject: |
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A Scope? Why not? As long as you don't touch the power resistors 
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 13, 2016 1:46 pm Post subject: |
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| the dude wrote: | | Quote: | | So the retrace lines should be very bright |
OK, -9 at the input of the OPA means +8 at the output. This voltage gets inverted again by the 2. stage. That means FULL cut off. The ABL loop thinks "Oh, no beam. Must turn G2 high". Notice that the negative rail is -2V while the positive is +8V, so -2V ist the max. negative voltage that the op amps can provide. |
Ok and -9 at the input of a 5166 dropped on the opa means +8 at the output too? Or was this calculated with offset and limitor?
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 13, 2016 1:53 pm Post subject: |
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I thnk I get you. Seems not so very complicated after all. The inverted opamp has a negative amplification. But we must let the blanking go to -5 V or so to get it operating with a 5166.
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the dude
Joined: 11 Sep 2013
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| Posted: Sat Feb 13, 2016 1:54 pm Post subject: |
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The +8 volts would be the "unclamped" voltage that appears on the output when you pull the inverting input to -9 V. So for your placement op amp, yes. In the original circuit it would be the voltage you set with the black clamp pot.
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the dude
Joined: 11 Sep 2013
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| Posted: Sat Feb 13, 2016 1:57 pm Post subject: |
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My idea is not to pull down the video to -9 V. Instead we can pull up the noninverting input via an adjustable pot. This will have the same result, but now we can adjust the blanking voltage without the need for clamping.
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 13, 2016 1:58 pm Post subject: |
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The offset is 3,2V the blanking 9V minus offset is 5,8V and that is close to the blacklimiting vallue set by p201.
So that means removing the clamping should not change so much?
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 13, 2016 2:05 pm Post subject: |
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You know that opa is not even so bad. At gain 1 it has 530 MHz. The hfa1100 has the same bandwidth at gain 2.
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the dude
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| Posted: Sat Feb 13, 2016 2:09 pm Post subject: |
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I don't understand this calculation....
Anyway, the OPA is a voltage feedback amp.
This is the circuit i suggest, it might work:
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 13, 2016 2:23 pm Post subject: |
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About the calculation on the + input of the opa there is a voltage devider givind a voltage of 1k2/(1k2 + 1k8) * 8V = 3,2V
That has to be added to -9V giving -5,8V time minus for amplifying -1 gives 5,8V right?
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redfox001
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| Posted: Sat Feb 13, 2016 2:27 pm Post subject: |
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Now that voltage is limited to the adjustable black limit at round 5V so what we have to do is change the blanking voltage to something like -8V to not need the limitor on the opa?
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the dude
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| Posted: Sat Feb 13, 2016 2:36 pm Post subject: |
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Ah, OK. There is the noninverting input, i forgott that.
My first tought was also to reduce the -9V, but maybe thats not good because the blanking switch is not well isolated from the input and this may affect stability. Not sure. Using the noniverting input also has the advantage of removing the blanking components from the input.
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 13, 2016 3:20 pm Post subject: |
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Ok that seems even better. I must say that in one discussion we have solved a lot of problems with the neckboards very good!
I am thinking that replacing the hfa1100 should be done even before anything else because it is much easier and migh give the same benefit in bandwidth.
I do remember that when I substituted the 5166 and the blanking was all wrong I could still see video so I tried a testpicture to see if this was the magical improvement and sadly I did not see so much but the rest of my chain was awfull to begin with. If we clean up the switcher and driver than improvement on the opa will be more visible but not miraculous I guess.
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redfox001
Joined: 16 Mar 2009
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| Posted: Sat Feb 13, 2016 5:53 pm Post subject: |
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I am not completely sure my calculation is right. Inverting opamp with offset. Looks like a differential opamp. V out = - V in + V off ? Would make it 12,2V
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the dude
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| Posted: Sat Feb 13, 2016 6:09 pm Post subject: |
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Oh, you're right... Anyway, it would be 8V.
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 13, 2016 6:19 pm Post subject: |
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Yes 
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the dude
Joined: 11 Sep 2013
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| Posted: Sat Feb 13, 2016 6:28 pm Post subject: |
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Today i removed the red gamma AD835.
Everthing is fine, no negative effects in color visible
But i found out a 1:1 horizontal pattern is still very dark and barely visible. There must be a real problem left in the video chain. Hopefully its not the video hybrid driver itself...
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redfox001
Joined: 16 Mar 2009
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Location: The Netherlands
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| Posted: Sat Feb 13, 2016 7:00 pm Post subject: |
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Do you have the internal moome?
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redfox001
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| Posted: Sat Feb 13, 2016 7:01 pm Post subject: |
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Did you not mean the vertical lines are dark?
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