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VDC 8" HighRes Projector - Page 3

post #61 of 101
Mike it looks almost like U4 on the old VNB can be elimintated, the Bright and spotkill circuits are still there on the new VNB The Spot kill has the same layout as on the old VNB now using M1(mmBT30904) and its complimentary Q3(MMBT3906), its the bright circuit i cant understand after the op amp U2, its different but i cant see how.

Also mike check out both 85 volt rails going to each side of the amp, on the old VNB there were 3 needed coming in to the transistors Q1 and Q 22 and the respective mirrored transistors on the other side at three points, now there is one more point added near pin 2 on Q22 but only from 2 sources not 3 like on the old VNB, here it gets split to three locations with D2 controlling them it seems?

Athanasios
post #62 of 101
The second clamp circuit on the neck boards can be completely disabled by simply removing R42. That is the resistor that feeds the vertical clamp pulse to the neck board clamp circuit.

Removing that resistor will lower the brightness on the neck board and the G2 may need to be increased.

I did get to run a few of my test patterns to see what the end result was, but would need to do further testing tomorrow.

So far, it looks like that circuit may be necessary on the stock boards, but it's hard to tell so soon in the testing with the few patterns I've used up to this point.

The lower range does jump out more, with the only problem I'm seeing being dark shading against white.


I'll get back to this tomorrow...
post #63 of 101
Quote:
Originally Posted by mp20748 View Post

The second clamp circuit on the neck boards can be completely disabled by simply removing R42. That is the resistor that feeds the vertical clamp pulse to the neck board clamp circuit.

Removing that resistor will lower the brightness on the neck board and the G2 may need to be increased.

I did get to run a few of my test patterns to see what the end result was, but would need to do further testing tomorrow.

So far, it looks like that circuit may be necessary on the stock boards, but it's hard to tell so soon in the testing with the few patterns I've used up to this point.

The lower range does jump out more, with the only problem I'm seeing being dark shading against white.


I'll get back to this tomorrow...

That was simple and quick!

i wonder how it will handle actual video with all its changing frequencies.
That is will it cause any issues?

Athanasios
post #64 of 101
Thread Starter 
does anyone know the pricing on those boards ?

and Scott, do you have employee discount ?


Michael
post #65 of 101
Quote:
Originally Posted by nashou66 View Post

That was simple and quick!

i wonder how it will handle actual video with all its changing frequencies.
That is will it cause any issues?

Athanasios

Well, not really. It's simple to disable the clamping, but it's not going to be easy to get things were they would need to be if not using the clamping.

For instance, I'm running several of my usual test patterns when looking at this problem.

One is the flash (full screen white, then black flash every two seconds). When using this pattern while watching things on the scope, when full white. The scope shows zero (zero) pedestal and no bounce in image with the neck board that has R42 removed.

On the neck board that has R42 in place, the pedestal does not move from it's set (set by clamp circuit) pedestal level. The clamping circuit keeps the pedestal at reference, but it bounces between full white then to black.

When using other test patterns and overlaying the amplitude (matching the signals IRE), the pedestal level of the clamped neck board is higher than the neck board that has R42 removed.

Also, when using the horizontal step ramp pattern, the neck board with R42 removed does not show even ramp bars from left to right. Just as the ramp gets darker, the top part of the ramp is brighter than the bottom part (R42 removed).

On the neck board with the clamp circuit in place, the bars are smooth and equal all the way across.

The overall viewable and measureable difference is the clamped board (R42 in place) has a brighter (elevated low end), while the board with R42 removed has a better low end performance, but there's a bit of distortion in the image as well as being shown on the scope.

Not sure what tse is doing to correct the shortcoming of not clamping that section on his new boards, so much work needs to be done to get even and smooth results with stock boards.

If I can get back to this I'll try and post a few shots hoping to show what I'm seeing beween the two boards.
post #66 of 101
Thanks for the Info mike. Do you think you might be able to decipher it from the new Schematics and some how come up with a fix for the older boards?

Athanasios
post #67 of 101
Quote:
Originally Posted by nashou66 View Post

Thanks for the Info mike. Do you think you might be able to decipher it from the new Schematics and some how come up with a fix for the older boards?

Athanasios

I'll do what I can. But I'm also thinking to keep the clamp in place and to look at lowering the pedestal instead. that way I could keep the benefits of both.

The better low end performance is worth going after. What tse has done with this is also what I've been saying for the longest, that a direct coupled video chain would produce the best low end perfornce because it's almost impossible to control and keep the various pedestals at reference along the chain.

Again, and I've been saying this for the longest. The marquees video chain is the absolute best for HD signal low end performance.
post #68 of 101
With R42 removed Q27 should always be off. That leaves no path for bias current for U4-5. I would expect it's output to end up at one rail or the other. That is going to put U1-7 at one of it's extremes. It might work better to lift the end of R36 that connects to U1-7 and connect a voltage that's about -1V or so. That will then become the offset control or BRITE.

Scott
post #69 of 101
Thanks TSE for the great information.

Just so I understand correctly, the 02-270340-01 part can be swapped in and used with a regular vim?

Thanks,
Dan
post #70 of 101
Quote:
Originally Posted by tse View Post

With R42 removed Q27 should always be off. That leaves no path for bias current for U4-5. I would expect it's output to end up at one rail or the other. That is going to put U1-7 at one of it's extremes. It might work better to lift the end of R36 that connects to U1-7 and connect a voltage that's about -1V or so. That will then become the offset control or BRITE.

Scott

Pure Genius !!!

Now where would we get the -1 volt from ? would we need to ad a new voltage source or can wee feed it from a different -V source and lower it to
-1.

Athanasios
post #71 of 101
Quote:
Originally Posted by tse View Post

With R42 removed Q27 should always be off. That leaves no path for bias current for U4-5. I would expect it's output to end up at one rail or the other. That is going to put U1-7 at one of it's extremes. It might work better to lift the end of R36 that connects to U1-7 and connect a voltage that's about -1V or so. That will then become the offset control or BRITE.

Scott

OK ,that's makes perfect sense. I'm also thinking to put a pot in there that'll allow for precise offset adjust, where I could set the level using the scope .
post #72 of 101
Quote:
Originally Posted by mp20748 View Post

OK ,that's makes perfect sense. I'm also thinking to put a pot in there that'll allow for precise offset adjust, where I could set the level using the scope .

I was going to edit that idea in my above post mike!! Now i'm thinking like you... this is scary !

Athanasios
post #73 of 101
Quote:
Originally Posted by Blorton View Post

Thanks TSE for the great information.

Just so I understand correctly, the 02-270340-01 part can be swapped in and used with a regular vim?

Thanks,
Dan

Yep. The '340 card will work with '338 and '339 cards. The 81771 will only work when using three '771. Both work with the standard VIM.

Scott
post #74 of 101
I'm doing something similar on my VIMs to re-set the offset on the first stage clamp circuit (TL071) once I replace the first stage OpAmp with a different IC.

Really blurred clamp section on modified VIM (can't focus that close)
post #75 of 101
Ohh I see, your just taking the -v to the op amp and lowering it using the resistor.
But on the VNB a trim pot would work perfect to find the correct resistance to use or the correct voltage drop needed to reset the offset. Could a zener diode also work once we know the value needed?

Athanasios
post #76 of 101
Quote:
Originally Posted by tse View Post

With R42 removed Q27 should always be off. That leaves no path for bias current for U4-5. I would expect it's output to end up at one rail or the other. That is going to put U1-7 at one of it's extremes. It might work better to lift the end of R36 that connects to U1-7 and connect a voltage that's about -1V or so. That will then become the offset control or BRITE.

Scott


One thing here, we still remove r42 and lift one end of r36 and add the -1V to the end of r36 that was lifted. correct?Or do we leave R42 there?

Athanasios
post #77 of 101
Quote:
Originally Posted by nashou66 View Post

Ohh I see, your just taking the -v to the op amp and lowering it using the resistor.
But on the VNB a trim pot would work perfect to find the correct resistance to use or the correct voltage drop needed to reset the offset. Could a zener diode also work once we know the value needed?

Athanasios

That resistor is in the mega-ohms.

Two images...

the first one is showing both neck boards over-layed on each other. Both have R42 in place.

the second image also shows both neck boards over-layed, but one has R42 removed. note the distortion and the lowest step lower than the other neck board.

Also note that the scope is externally synced to vertical. So when I increase or lower the BRIGHTNESS control on the remote, the entire image moves up and down in reference to the sync.




post #78 of 101
Damm you guys! I thought that i could take little pause of all this modding stuff
post #79 of 101
Quote:
Originally Posted by nashou66 View Post

Ohh I see, your just taking the -v to the op amp and lowering it using the resistor.
But on the VNB a trim pot would work perfect to find the correct resistance to use or the correct voltage drop needed to reset the offset. Could a zener diode also work once we know the value needed?

Athanasios

Put trimmer about 22k-50k between +5 and -5 (extreme pins) and take variable voltage out at center pin, middle position is 0 volt.
post #80 of 101
How about this kind of config. This cuts clamp away but leaves brightness control and spotkill should work also? trimmer allows adjust pedestal to right level. I was little worried just to pull out that R36 and feed "pedestal voltage" to that line (spotkill doesent work then)

Comments?
LL
post #81 of 101
Quote:
Originally Posted by 1031 View Post

How about this kind of config. This cuts clamp away but leaves brightness control and spotkill should work also? trimmer allows adjust pedestal to right level. I was little worried just to pull out that R36 and feed "pedestal voltage" to that line (spotkill doesent work then)

Comments?

Yes, that circuit would do fine to correct/adjust pedestal, but adjusting the pedestal there I'm thinking is not why they're using that S/H circuit.

A clamp section here makes no sense in this section, so there must be something else going on here...

Look at my two test patterns. In them I'm showing two signals overlapping each other. I'm show them with both boards having the circuit enabled, and I'm also showing one with the circuit disabled.

The one showing the circuit disabled also shows a crippled low end linearity. Crippled meaning the low section of the tes pattern is not linear. To be linear, each step (bar) has to have equal space from the other. If you look at the bottom of the patterns, the spacing decreases on the last two bars.

That is the same linearity problem I've been talking about for the longest. based on the two comparison patterns, the S/H circuit seems to only correct the lower end of that pattern. The pedestal is irrelevant here, because it can be adjusted with the brightness control. And though the circuit also effects the pedestal, it's not effecting it to point an entire circuit should be needed to correct it.

Non linearity seems to be one of the drawbacks with direct coupling circuits. I was of the thought that R90 and R91 was the tweak to smooth things out on the boards, but it looks like they're also using that S/H circuit as well.

I can also understand why tse is not using the circuit. The problem has a lot to do with the components being used. By simply swapping in another IC for U2, you also risk throwing off the low end linearity. he must be doing something to control this well, because the older chips were terrible with linearity in direct coupled stages. The newer ones maintains the linearity way better, but still may need a bit of help.

Keep in mind. The linearity issues I'm talking about is fine for VESA and computer graphics applications. It's only a problem with HD signals and bringing out the best in low end detail and performance.


I'll get back to this later, but for now. I see need to keep the circuit in my boards.
Oh, you can also control the offset by using variance at pin 3 of IC 4 (10K pot to +/- 14 rails of U4 - w/100K to pin 3.

I plan to look into making a linearity pot to smooth out that lower end. for HD signals the goal should be to have each step exactly the same spacing from each other.
post #82 of 101
At one it was into my mind that it would be a Protection circuits.
So wold it be like the issue i had on my one Vim we talked about before, where one of the circuits can act as a radio receiver and the high frequencies can cause the spotkill circuit to come on and off depending on the frequency content of the Video.

But now i am totally confused!!
post #83 of 101
Quote:
Originally Posted by amidcars View Post

At one it was into my mind that it would be a Protection circuits.
So wold it be like the issue i had on my one Vim we talked about before, where one of the circuits can act as a radio receiver and the high frequencies can cause the spotkill circuit to come on and off depending on the frequency content of the Video.

But now i am totally confused!!

Not really sure what you're asking here, because you did not say what your problem was.

If you want to better understand the spot kill I'd start at the neck boards.

The attached image would help in where to start.
LL
post #84 of 101
Quote:
Originally Posted by amidcars View Post

At one it was into my mind that it would be a Protection circuits.
So wold it be like the issue i had on my one Vim we talked about before, where one of the circuits can act as a radio receiver and the high frequencies can cause the spotkill circuit to come on and off depending on the frequency content of the Video.

But now i am totally confused!!

\\\\

Spammer!!!!!!!, he copied my earlier post from a different thread i think.

Athanasios
post #85 of 101
So Mike have you done anything more with this?


Athanasios
post #86 of 101
Quote:
Originally Posted by mp20748 View Post

However, when dealing with HD signals, there's something with it's transcoded digital tri-level sync (all HDTV signals are transcoded digital component), that can create another problem along the signal chain...


Mike, why do you keep going on about 1080i component tri-level sync?


Most are watching Bluray through a VP running a custom resolution, or via a PC.

I can't see how component style tri-level sync is relevant to anything anymore.
post #87 of 101
Is this what you are talking about?
VDC Marquee 8500 Ultra Long Bow Projector
eBay item:VDC Marquee 8500 Ultra Home Theatre CRT Projector NEW! (#260431625985)
post #88 of 101
Quote:
Originally Posted by David1 View Post

Is this what you are talking about?
VDC Marquee 8500 Ultra Long Bow Projector
eBay item:VDC Marquee 8500 Ultra Home Theatre CRT Projector NEW! (#260431625985)


I dont think My longbows use the special HR tubes. According to TSE the rest of the PJ is the same just the tubes are special High rez and are quite expensive compared to regular 8" tubes. I should take of the upper cover on the tubes and have peak at them.... i'm curious now.

Athanasios
post #89 of 101
Quote:
Originally Posted by tse View Post

You know, it would be alot of fun to design stuff for home theater use but VDC makes its money from the simulator industry. So almost all of the new stuff is little use to most people here. Giant, powerful convergence amps, a monochrome projector that makes a picture about a foot square for head up display (HUD) of fighter plane instruments, a vertical deflection bd with crazy linearity controls for curved off axis screens. Alot of stuff for curved screens.


But, along the way we used up all of the Motorola transistors that are used on the neck card and had to design a new one. Since the decline of the CRT monitor industry video transistor selection has dried up. I am happy to say that the new card is equivalent to the old one with bandwidth good enough for QXGA (pixel clock=240MHz). The design is very similar to the old one, it really cant be much different. It has been in production for at least a year, I'm surprised that no one has got their hands on one and asked about it in the forums.


Scott
LL

LL

Just got a set of these!!! Not in hand but will get them for a few weeks.

Athanasios
post #90 of 101
Pretty cool. You will have to run the remote control brightness a little different than the original cards but don't let that bother you.

Scott
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