Marquee Modifications and Performance Enhancement 3 - Page 7 - AVS Forum
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post #181 of 465 Old 07-02-2004, 05:10 AM
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Mark, yeah, either that or we could probably play around with the gain on the preceeding clc449/replacement opamp.
Vic

PS Mike, could you please empty your mailbox? Its full.
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post #182 of 465 Old 07-02-2004, 05:25 AM
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Aren't you guys talking about two different things? Mike is talking about relays, and Jaehong is talking about the sd5401. And I believe Jaehong earlier mentioned that he just removed the in-line section from the circuit and jumpered it, so there really should not be a change in brightness.

Even if the switch had a 75 ohm insertion loss, that output line connects directly to the contrast multiplier, which has an input resistance of 25k so level should not be noticeably changed. That's a curiosity that probably should be checked out. Jaehong, if you have an -02 VIM you might check to see if the 100 ohm resistors R1000, R1001, R1002 which shunt the first stage output to ground are there. If they are not, that could explain part of what you saw when jumpering the switch. Some early boards don't have those and should. The -03 boards already have them, but as R41, R42, R43.

Also, I tend to agree with Mark that the differences being made in the circuit, cabling and quality of source are going to far outweigh the effects of the relays. If they were cheesy little things I could see it, but these don't seem to be. Heck, the type of BNC connection you get (times however many you have between source and projector) would be more significant.

--Bill
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post #183 of 465 Old 07-02-2004, 08:07 AM
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Bill,
I believe that Mike is talking about replacing the portion of the SD5401 that is in the signal path with a relay, similar to what you suggested earlier (Mike correct me if I'm wrong here). Thanks for the information regarding the input resistance to the multiplier - given that, the internal resistance to the SD5401s definately seems like it wouldn't have any affect here, and the brightness issue should be checked out if we encounter it again.

If we are talking about replacing relays (which I'm pretty sure we arn't - I talked to Mike earlier), then I completely agree with you that they don't seem to be worth it - thats why I removed the relay removal section from my VIM mod post.

At any rate, I hope that the SD5401 signal bypass does have a significant effect (although I acknowledge that I could be wrong here, and it might not), as this would ultimately lead to an even better image.

Thanks,
Vic
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post #184 of 465 Old 07-02-2004, 08:58 AM
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Oh, gotcha. I didn't get that. But that would have to be just for testing, correct? As you pointed out earlier, the v-sel line would be toggling at a rate much higher than the relay could handle, plus if I'm understanding this correctly, the timing of off to on cycles of v-sel would determine whether the displayed video is totally internal, totally external, or external with an internal window 'overlayed' in a particular place on the screen.

I really want to switchably hardwire those three paths, but haven't been able to get to it yet with a reasonable approach.

--Bill
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post #185 of 465 Old 07-02-2004, 09:10 AM
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Bill,
I think that we could probably filter the retrace switching signal out, near the resistor R193 (add a low pass filter there for a reasonably low frequency and try it out - lower the frequency if needed - this is the resistor on the v-sel line in the section of schematic I showed earlier, near the XOR gate, and is common to all three colours). This shouldn't have any effect on the DC ground signal sent when we are in the internal menu. Also, the video is muted via the clamp signal anyways, which causes an output of 0 volts during the clamp phase (backporch), and -120mv at retrace. If this still causes brightness increase, we can deal with it then (hopefully it won't, but we'll see).
Vic
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post #186 of 465 Old 07-02-2004, 09:17 AM
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So many things could be changed. Rather than identifying those things we need some sort of end goal.

No special order but as an engineer I need to know what they want.

Better PQ? What the hell exactly is that and then I need to correlate how that can be accomplished without reference to a particular circuit.

For example, increased bandwidth. lower video noise, less distorted RGB, increased linearity, less contamination irrespective of noise, such as elimination of RGB crosstalk, less DA by the blocking caps etc etc.

Obviously there is much more but in order to design circuit modifications, even just substitution of better parts with the same values, I need direction as to what parameters I need to make better to get a better PQ.

Suppose I want to increase MPG in my car without sacrificing acceleration etc.

Well I can lighten the vehicle or increase its aerodynamic efficienct. Changing from cloth to much more expensive leather seats won't help.

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post #187 of 465 Old 07-02-2004, 09:28 AM
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Mark,
At this point, I'd say my end goal is to squeeze every bit of performance (all of: increased bandwidth. lower video noise, less distorted RGB, increased linearity, less contamination irrespective of noise, such as elimination of RGB crosstalk, less DA by the blocking caps etc etc)
from the Marquee in the time and budget I have to do it without sacrificing the reliability of the projector.
Vic
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post #188 of 465 Old 07-02-2004, 09:59 AM
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Mark,
I can't say that I'm entirely sure what your point is.

One of the goals here is to explore what existing components or designs are compromising the analog signal quality. Some suspects will and others won't. I'm sure that at an engineering level, the basic design is quite superb (as proven by its longevity), but undoutedly compromises were made with respect to cost of components used, availablity, possible manufacturing constraints, etc. Even circuit topology would have been affected to maintain a reasonable manufacturing cost. And of course, there's the age of some components that adds a different element of surprise.

Some things are formula, other things may look great on paper but not in execution, and in rarer cases just the opposite. Some engineers would disagree with the significance of certain types of changes. So without getting into a complete re-design, new boards and all, we believe there are numerous small improvements in the analog video chain which when taken as a whole would be quite significant. As in your leather seats example, we're not looking at the convergence or stigmator boards to improve the analog performance -- that would be silly. There are only four boards in the projector where analog video is processed, the VIM and 3 VNB's. Other improvements might be made in other areas, but not to analog video.

So, THE GOAL is better picture quality, followed by better picture quality, and then better picture quality. Oh, did I mention better picture quality?

Of course the tubes, high voltage, mechanical alignment, electrical alignment and other factors enter in to a total definition of picture quality. However we're mostly taking those for granted at this point, making the assumption that the mechanical and electrical setups are as good as they can get or reasonably close, tubes are good and prefereably OEM, screen is good, etc. We're targeting the weakest link, analog video processing.

--Bill
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post #189 of 465 Old 07-02-2004, 10:09 AM
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Quote:
Originally posted by mark haflich
So many things could be changed. Rather than identifying those things we need some sort of end goal.

No special order but as an engineer I need to know what they want.

Better PQ? What the hell exactly is that and then I need to correlate how that can be accomplished without reference to a particular circuit.

For example, increased bandwidth. lower video noise, less distorted RGB, increased linearity, less contamination irrespective of noise, such as elimination of RGB crosstalk, less DA by the blocking caps etc etc.

Obviously there is much more but in order to design circuit modifications, even just substitution of better parts with the same values, I need direction as to what parameters I need to make better to get a better PQ.
Mark,
Very well put.

As far as mods go, improved PQ seems to be the logical goal. The larger the screen, the greater the payoff. As with many of the threads, it seems difficult to keep a thread on track. Someone will post a good thought, slightly off topic, and the thread bounces in that direction and then another and so on and so on. Would it make any sense to use this thread to discuss the direction of mods, increased bandwidth. lower video noise, etc., rank their importance, then start individual threads on each specific targeted improvement?

Every one has a different system to produce the video signal for the projector, different equipment, different cables etc. Then there is the actual setup of the projector, getting the best out of what you have in hand. All tubes are different, one may have good OEM tubes and a problem with the signal that produces a reasonable picture while another has a great system with a projector with OK rebuilt tubes (old glass) the MP mods and a great picture.

-Where does one start with a basically stock projector (with only the "Marquee Maintenance" upgrades) that seems to produce a great picture?
-Are the HVPS and Neck-board resistor changes maintenance or mods and necessary before any VIM mods?
-Has there been any definitive resolution on configuration of the resistor changes as to Carbon film vs. Ceramic?

Glen Carter
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www.ISFHT.com
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post #190 of 465 Old 07-02-2004, 02:03 PM
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Glen,
While everyone has a different setup, I think we all agree that picture quality on the highest quality input signal - rgb - should be the main focus of any performance inprovements, as that is where we will most likely actually detect the differences. That said, if you want to increase the performance of all inputs, the neck boards and HVPS are a good place to start, and so far, the resistor mods are the only publicly tried and true major ways of doing this. As for the issue concerning the differences between ceramic and carbon film, unfortunately, no one has tried the difference out yet, but the concensus seems to be that both produce results significantly better than the original carbon compositions. The ceramics that have been tested do drift with temperature more than the carbon films, so anyone wanting to test the differences and comment on them should take this into account, at least in reference to the neck boards. Also, care must be taken to use resistors that are specced for high enough voltages. Unfortunately, although I would like to be able to, I cannot contribute on the experimentation front at the present time, as I am at my parents home for the summer, and also do not currently own a Marquee.
The same current lack of trial and implementation concerns most of the mods contained in my posts at the front of this thread as well, for the same reasons (although the power supply/rail decoupling capacitor mods have been tried many times, if you look at the threads I reference in the first post). If you wish to try things out for us, you are welcome, and it would be greatly appreciated, although please be careful. Other than that, though, we have to wait for other pioneering type people like Bill, Mike and Jaehong to try them out first in order to gauge the actual discernable amount of difference. Once I get a Marquee, I will start trying things out as well, and hopefully by September, we will have most of the answers to the questions.
Vic
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post #191 of 465 Old 07-03-2004, 01:33 AM
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Hi guys,

I'd like to add my comments to the last few posts :D I have two
Marquees. One is a 8110(7500) converted to an 8500 and the
other is a 8500 Ultra Non-LC. The 8500 is my PJ to play with,
whereas the Ultra will turn into the finished "gem" (I hope :D)

Both Mark & Glen put on some interesting questions. I restore old
tube radios and amplifiers. I have also restored old cars. The only
satisfiying way (for me) to do something like this is from ground up.
This basically means tearing the PJ apart completely (already did
that :D) and going through each and every part. The only real problem
doing so is that it take a LONG time to finish. Testing the mods is,
other than lack of time :( , easy, since I have two PJ's :D. My real
problem is that I try to be a bit of a perfectionist, which of course
increases the time spent on a project (e.g.: I ripped the chassis
apart completely and deburred holes, filed away the sharp edges
on the stamped aluminium parts, etc) Bill has already read a bit of
what I have written, so he has an idea of the amount of work. ;o))
What I have done with the chassis, won't increase PQ, it won't
increase reliabilty, but it makes it prettier, reduces the risk of cuts
and nicks while working on the unit and it is generally more satisfiying
(to me). Of course, I don't know how many people will go to such
lengths :D

While Bill is correct in mentioning only the VIM and neckboards as
directly processing analog video, there are other parts that indirectly
touch the PQ. One example is the HVPS. So I think we do need to consider
all circuits and parts within the Marquee. As stated my Ultra is Non-LC,
so I will be looking into the optical and mechanical "path" from the
tubes through the lenses to see if I can't improve something there
(e.g. flat black paint, closing the gap between lens and tube, etc)


@Mark Haflich:
As to a pure engineering standpoint: I DO understand what Mark is
saying, but I have seen to many engineered products, in which the
engineers forgot the simplest of things. I have also designed circuits
that looked excellent on paper, yet in real life didn't work the way they
should have. Of course, as Bill already pointed out, EVERY commercial
product will have some cutbacks or reduced performance, simply because
of $$$ for the manufacturer. 10 cents saved here and there simply amount
to a LOT of money when going into production. The beauty of AVS is that
there are so many people with ideas on this list, that we have a wealth of
information to scoop from. Discussions and experiments will prove which
mods are worthwhile and lead to a better PJ. These are the approaches
which differentiate between an engineer and a tech :D In Germany we
have a saying "Probieren geht ueber studieren", which simply means
trying and testing goes beyond pure study of the matter.


@GlenC:
You are 100% correct that the threads wander off here and there (sort
of like now :D). But there is nothing you can do about it. Such OT
discussions are necessary and actually help keep the goal in sight. This,
of course, makes it difficult for follower modders. I have been collecting
threads that have to do with Marquee (and I'm SURE I don't have all of
them :D) When our mods and maintence have reached their peak,
someone will have to condense all the vital info into a manual, which can
be used as a guide in the future. You ask where does one start. I think
its most vital to start with reliability. That is clean out the gunk, fix up
solder joints, clean the contacts, replace parts in question, etc. This is esp.
important if you will be modding the unit. Just imagine doing a mod and
then finding out the PJ doesn't work anymore or PQ decreases. How are
you going to pinpoint the problem w/o knowing if it was the mod or some
other problem not releated to the mod at all (that's one of my reasons
to go the ground up route)?

Greets,
Reinhard

Gimme a hot soldering iron. I got work to do ;o}
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post #192 of 465 Old 07-03-2004, 04:12 PM
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I just wanted you guys to know that, as an owner of a BarcoGraphics 808s, I am jealous of this thread. :(

- Chris
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post #193 of 465 Old 07-03-2004, 05:18 PM
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Vic & Reinhard,
I appreciate your comments, but the meaning of my questions did not get through. I have a 9500 that I have done all or most of the maintenance and reliability work. The product resulting from that alone can make one think why or how could anyone improve the picture I have.

My question was more in the line of when we get to mods, what seems to be an effective sequence? A-B-C.... where C builds on B and B builds on A, but where C alone may not be effective.

Agreed, RGB improved picture quality is the goal.

As for the reference to the HVPS and neck-board resistors, just wondering if it would be appropriate to reference that in the "Marquee Maintenance" thread because it seems more of a maintenance/reliability step.

One of the advantages we have here is, input from an engineer is a "theoretical/textbook/experienced" look at the issue put out for discussion. The threads are not the corporate environment where the engineer is trying to sell his approach (my design is better than yours) or to cut costs. I think, starting to resolve an issue from or using the theory and/or the "as engineered" state, gives direction and meaning to the resulting discussions and fuel for improvements. Much better than, 'I tried this and my picture was much better'.

Now, my turn to deviate a little. What has been determined to be the best method to replace the coax from the VIM to the Neck-boards? Re-use the existing mini-RCA plugs and replace the coax?

Reinhard, any chance you work on old Porsches?

Glen Carter
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post #194 of 465 Old 07-03-2004, 05:59 PM
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Well stated Glen.

Mark Haflich
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post #195 of 465 Old 07-04-2004, 01:40 AM
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Chris, please read the first couple of sections to my posts on the first page if you want some information that could possibly help you out.

Reinhard, thanks for the excellent thoughts - I have tried to somewhat address the other circuits that affect video performance by suggesting a few changes to the focus and control boards so far. Also, I have to say that your work sounds like it will be a lot of fun reading about, and I also appreciate your thoughts on tackling the reliability standpoint first and foremost, because, as you say, it becomes difficult to troubleshoot problems when you are unsure if they arise due to modifications or pre-existing problems.

Glen, I have tried to address some of the theory in the front posts, although my understanding is probably not 100%, as I am not an engineer. That said, I try to rationalize as best I can and come up with plausible reasons that things might improve if I change a certain component, etc. I think we are trying to increase bandwidth (read the second link I provided at the front talking about video signal harmonics to see why), lower noise and distortion in all circuits that could affect RGB performance (ie. VIM, focus, HVPS, etc). The HVPS is indeed already covered in the maintenance thread. Also, from my own standpoint (feel free to disagree), it is basically debatable either way to say it is a maintenance issue versus a performance improving modification. As far as your question regarding the connectors, my feeling from reading the maintenance thread, and several other comments about mini coaxial connectors, is that they should be changed out to better ones, and the cable replaced as well. From what I remember reading, mini-coax connectors cannot, due to their dimensions, be true 75 ohms. Therefore, If anyone can come up with a good way to use full size connectors on both the VIM and neck boards, or find a much improved mini coax connector, it would be appreciated. Also, bear in mind that, from a performance standpoint, soldering the cables would be the ideal solution, although this would prove to be a pain in the future when you needed to remove the VIM or neckboards.
Vic
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post #196 of 465 Old 07-04-2004, 05:39 AM
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Glen,
I've spent the last couple of days searching for the so-called "mini-rca" jack and plug to no avail. And I'm not all that sure that it's even a suitable thing to have there in the first place. It looks like an ordinary audio product adapted to video and is undoubtedly a weak spot. It isn't likely to be 75 ohms, either.

The problem is that finding something that small that will mount similarly (in a 4mm hole, basically) hasn't proven to be all that easy either. Selections are further limited by the 75 ohm impedance requirement.

I'm beginning to think little pigtail leads to standard in-line BNC-type connectors would make more sense rather than these mini-rca's, but that brings into focus different problems such as more soldering transitions, the way in which to secure the inline stuff on each end in a way that it is safe from accidental shorting to chassis or another component, but still convenient to separate for removal of the VIM or a VNB, etc.

Then there's the cable. They're using the mil-spec version of RG179 which is actually quite different from RG179 -- higher loss, insufficient shielding, etc. RG179DT would be an improvement if you did nothing else. We've been using Commscope 73501S as a replacement, but in recently looking at its specs I think we can do better yet with something like the Belden 1855a.

So at the very least, you could put Commscope cable or real RG179DT on the existing connectors and have an improvement, or wait for a better solution when it comes along.


Disclaimer: The above represents my own opinions and some shared by a few other individuals. The Engineering Committee has not approved, nor does it endorse these modifications. Further, these modifications have not been shown to have any effect whatsoever in laboratory tests, which have not been performed. :eek:

--Bill
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post #197 of 465 Old 07-04-2004, 05:48 AM
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Hi Guys,

@chrispy:

That's the intention :D No, seriously, Barcos aren't uncommon PJs.
There has got to be a way to round "your set" of experts for a
similar discussion. As a matter of fact, look at some of the URLs
Vic posted at the beginning of this thread. They have to do with
Barcos :D

@GlenC:

BTW: You have a PM :D

>My question was more in the line of when we get to mods, what
> seems to be an effective sequence? A-B-C.... where C builds on
> B and B builds on A, but where C alone may not be effective

Ah, now I see. This is indeed a sort of stumbling block. However,
I think Vic's approach is pretty good. He is looking at the video
chain and going through from the BNC connector up to the tubes,
which seems to be a sensible approach. I would call these primary
mods. I think following the video signal from the input connector
through all the circuit "stages" up to the CRTs is a logical sequence.
(i.e. examing PQ after changes made from stage to stage). A good
example are the SD switches. There is no sense in keeping these
and then trying to get rid of the noise by modifing the HVPS (e.g.) All
other mods (HVPS, control board, etc) would be secondary mods, as
they are not directly linked to the analog chain, but still have some
effect on the noise within the PJ.

Oh BTW: I didn't mean to bash engineers :D It's just that some are
so caught up in their math and specs, that they often miss the design
as a "whole thing" I have a VERY good friend who is an engineer and
a very good C programmer, but if I put him up to a broken toaster
(okay a bit of exaggeration on my part :D) he's lost.

>Now, my turn to deviate a little.

Since it's in the video line, I wouldn't call it deviation.

>What has been determined to be the best method to replace the
>coax from the VIM to the Neck-boards? Re-use the existing mini-
>RCA plugs and replace the coax?

While I dont have the answer, I have been looking into SMA and
SMB connectors. They seem much more reliable. I have ordered a
few to see if they will fit (spacewise). These connectors are good
up to 3 GHz and I have used them with great sucess on a 2.4Ghz
model rocketry A/V & telemetry transmitter which I built. While I
haven't scoped this (no VIM extender board), it would not surprise
me if the mini-RCA's cause some signal overshoot. I know that the
SMA & SMB connectors are not 75 ohm, however, after looking at
some scope charts from Canare's (I believe) "tru 75 ohm" BNC
connectors, it doesn't seem to be that important to have a perfect
match. Canare shows good improvements when compared to regular
50 ohm BNCs above 450 Mhz. This is way above the PJ bandwidth
and WAY above any video signal we will ever throw at the PJ.

@mcpherv:

>Reinhard, thanks for the excellent thoughts - I have tried to somewhat
>address the other circuits that affect video performance by suggesting a
>few changes to the focus and control boards so far.

Yup, I saw those. As stated above, I really like your approach of going
through the whole video path from A-Z. I sure that every circuit can be
improved in one way or the other. The only real problem I see is that
it will become harder and to see an improvement in PQ as we go on.
Simply because the changes will become less and less radical.

>Also, I have to say that your work sounds like it will be a lot of fun
>reading about, and I also appreciate your thoughts on tackling the
>reliability standpoint first and foremost, because, as you say, it becomes
>difficult to troubleshoot problems when you are unsure if they arise due
> to modifications or pre-existing problems.

I learned that the hard way :D :D I will make the PDF publically available
as soon as it contains more info. Right now its like a diary of what I have
done to the Marquee and it is still mixed up and contains no references of
which mod depends on which other one. Since I will be using info from
posts of other AVS members (you, bblue, Guy Kuo, mp20748 to name a
few), I will also need to get their okays before I can release it. What I am
trying to create is a manual that contains all vital info on Marquee's from
disassembly to maintence to modding all the way up to final adjustment.
I don't know if it ever will be finished or if I can even keep all the promises
I am including :D


Greets,
Reinhard

Gimme a hot soldering iron. I got work to do ;o}
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post #198 of 465 Old 07-04-2004, 06:06 AM
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Quote:
Originally posted by Lightningman
The only real problem I see is that
it will become harder and to see an improvement in PQ as we go on.
Simply because the changes will become less and less radical.
Which can be referred to as the law of diminishing returns.
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post #199 of 465 Old 07-04-2004, 06:08 AM
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Hi,

Addendum to SMA & SMB connectors:

Here are a few sites that deal with these connectors: They also
seem to be available in 75 ohm types.

h t t p://store.hawkesintl.com/smaconnectors.html
h t t p://www.amphenolrf.com/products/mini75ohm.asp
h t t p://www.emc-nc.com/prod15.htm

Greets,
Reinhard

Gimme a hot soldering iron. I got work to do ;o}
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post #200 of 465 Old 07-04-2004, 12:56 PM
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Bill, thanks for the information on the internal cables - they definately seem to be in need of replacment, then (not that I think there was much of an issue with this anyways, as several people have tried it). I was also thinking about a similar idea for using full size connectors on the VIM and neck boards, but as you say, we would need to figure out a way of doing that without grounding anything in the projector. The other option of course is to see how the ones Reinhard posted work out for now.

Reinhard - thanks a lot for finding those links for the connectors - let us know how they work out. It seems youre putting a lot of work into this, and I really do look forward to your manual if you get it done :) . I do agree with you that we will get into a state of diminishing returns, but hopefully that won't happen too soon. We'll see, though. Lets hope there are one or two significant mods left for us to find.

Vic
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post #201 of 465 Old 07-04-2004, 02:17 PM
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Reinhard,
I've been looking at the SMA/SMB/MCX type connectors but there seems to be two things getting in the way of using those. The strict wire size or type requirements, and the specific tools needed to assemble them. They seem to be just too limited unless you want to stick with RG179-type wire.

Have you run into any that can accomodate a larger cable and be assembled manually?

--Bill
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post #202 of 465 Old 07-04-2004, 02:56 PM
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Hi Bill, Vic, all,

Quote:
Originally posted by bblue
Reinhard,
I've been looking at the SMA/SMB/MCX type connectors but there seems to be two things getting in the way of using those. The strict wire size or type requirements, and the specific tools needed to assemble them. They seem to be just too limited unless you want to stick with RG179-type wire.

Have you run into any that can accomodate a larger cable and be assembled manually?

--Bill
There are non-crimp type assemblies out there. I have a link for
a german distributor, but haven't looked for one in U.S.A. :D
However, these too are for RG179. I don't think crimping is that
bad. You do need to pay attention to the type of crimpers used
and that you go per manufacturer's specs on removing the
insulation. Over here SMA and SMB are commonly used in cell
phone technology (in car systems, etc).

I was just about to write:

"As to the RG179, do you really think its that bad? I mean we are
talking about some length <<12 inches long"

but I decided to download the Mil spec sheet before I opened
my mouth :D . Geez, RG179 does indeed suck in terms of capacitance.
23pF PER FOOT :eek: :eek: . Attenuation isn't that bad, but I never
would have imagined that the cable capacitance would be anywhere
NEAR that high.

The problem is that we don't have a lot of space in that area for a
much larger connector :eek: Neither on the PCB itself nor around
the rack where the VIM is inserted into. I also see no way of putting
a connector on the neckboard (instead of the VIM) and it would be
much more of a PIA to pull out the VIM, because you would need to
get to the neckboards first. Putting a connector midway on the cable
(i.e soldering the ends of the cable to both the neckboard and the
VIM) dosn't really find my liking either, since you would need to insulate
the whole connector (both male and female sides) with say heat shrink
tubing, which would once again be a PIA to remove the VIM.

The question is if there is a small diameter 75 ohm coax wire out
there with less capacitance per foot (I really can't image it getting
any worse than 23 pF per foot). Even if not, I would still imagine
that the SMC/SMB connectors themselves would already improve
signal quality, tho.

Greets,
Reinhard

Gimme a hot soldering iron. I got work to do ;o}
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post #203 of 465 Old 07-04-2004, 03:10 PM
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Reinhard,
The RG179DT capacitance is down around 17pf/foot, Commscope is about 16pf. That mil spec stuff is also stranded instead of solid conductor, and one one shield at 94% coverage. That's not sufficient for the levels the cable handles and the emf in the close vicinity.

The 179 family is about .105 OD, and the Commscope is .159 OD. The cable that looks the best to me is the Belden 1855a which is classified as sub-miniature rg59, with an OD of about .175. Not too bad when you consider the solid 23 guage center conductor, capacity of 13pf/foot and dual shield with 100% coverage. You could probably squeeze it into the mini-rca's in a similar fashion as you would with Commscope, but it may be too large for the SM type connectors.

It's really a quandry. Still, you could stay with RG179DT and use and SM type connector but I think only on pigtails. There are some pretty low profile units, but I'm not sure how the heck you would attach them to the existing PC boards.

--Bill
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post #204 of 465 Old 07-04-2004, 06:52 PM - Thread Starter
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I have used Audio Quest VDM-5 silver core 75 ohm cable.

the reason I used is that it has pure silver core and very good shiled.


The result is diffcult to evluate since I modified other parts together.
It is very expensive( 400$).
I don't want to recommend much becouse of cost performance reason.


You can see photos which was taken during replacing cable.
http://www.kavforum.com/Visual/Scree...e=&SearchName=
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post #205 of 465 Old 07-05-2004, 09:00 AM
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This might seem like a dumb question, but what would be the total propagation delay going through a chip, say like a CLC449? In the specs there doesn't seem to be a direct correlation, except for phase and settling times.

--Bill
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post #206 of 465 Old 07-05-2004, 10:02 AM
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Bill, I saw your comment about gamma in the 5700 thread- let me guess, you're looking at the gamma circuit?
Vic

EDIT: Never mind, it doesn't seem phase is linear with frequency, so calculating time delay that way wouldn't really work, I don't think. I also can't find it in the clc449 datasheet, or the THS3201 sheet.
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post #207 of 465 Old 07-05-2004, 10:44 AM
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I don't know either. I would think the phase spec would be relative to itself, meaning its 1 Hz output relative to its 500Mhz output (for example), not output relative to input. I didn't see anything in specs that spoke of time except phase and settling, and neither of those seemed right.

Yes, I was wondering about the additional gamma circuitry (not because of the other thread, though) introducing a delay that was never quite compensated for. But obviously it would be small. When I explored time vs cable length, it seems to be about 1' = 1ns.

When I look at very narrow vertical pulses on the pj, blue is always ever-so-slightly more present even when convergence is right on. I don't think that would happen unless it was shutting off slightly late, so I was wondering just how much of a delay one IC creates. It could be a total non-issue, but I thought I would ask just to settle my curiousity if nothing else.

--Bill
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post #208 of 465 Old 07-05-2004, 10:45 AM
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Just use a search engine with keywords "National CLC449" or whatever, and it will pop right up.

--Bill
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post #209 of 465 Old 07-05-2004, 11:05 AM
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Bill, if that was referring to me, I said I couldnt find time IN the sheet , not the sheet itself :D . I had actually thought of this a while ago, as well, but I honestly don't know enough in order to make a judgment call on it. Do you have an older MP'd VIM without the gamma to compare to? Either that, or maybe you could take the gamma circuit out by bypassing it with coax, etc? Just a thought.
Vic
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post #210 of 465 Old 07-05-2004, 11:26 AM
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You want the gamma circuit (which affects only the blue tube) because it greatly improves gray scale tracking. BTW I believe (but am not sure) the blue phosphors have a slightly long decay time than the red and green.

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