CurtPalme.com Home Theater Forum

[9kids]

Those Teledyne RF100's are like $45 bucks a piece, a little pricy. They have some rated to 1GHz that are only $23, maybe they would work.

http://www.teledynerelays.com/electromechanical/712.asp

[Nashou66]

You would only need up 500hz i'd say so the 1Ghz should be fine. So your going to go through with this 9Kids? Great if you do! for now I am just sticking with the digital input to the moome and it does look very nice with out that Cap. Have you thought about what I asked if we could use the pad where we remove the one 39k resitor for a noise filter cap off the input source. I dont think it would hurt the signal since its not in series, that is the signal wont run through the cap as before . It kinda be like a de coupling cap used on the power supplies. Is my line of thinking correwct or wont it make a differnece?
Once this is done we can add it to the new thread I started. I want as many new ideas to be added by guys like you.

Athansios

[WTS]

Don't forget if you start adding caps across the input you'll kiss your BW goodbye.

[Nashou66]

Walter so if i add a cap in the spot were resitor 175 was removeed in my picture a few post back that would alter the band width? even if its not in series with the signal just conneting it to ground? Can you explain a bit so i can grasp this? I'd like to learn as much as possible

Thanks

Athanasios

[9kids]

Athanasios

The video signal can have very varying bandwidth requirements. The lowest freq would be something like an all white screen, so each scan line or all 1920 pixels would be at 700 mV (100IRE), so the signal would look a little like a square wave with the signal only going to 0V during front & back porch and retrace. So the lowest bandwidth requirement is like the horizontal refresh rate or the even lower vertical refresh rate. The highest Bandwidth is vertical 1 pixel lines, which looks like a square wave of 960 700mV peaks with 960 equal 0V in-between, all in the space of 1 scan line.

The output of Moome’s DAC probable already has some filtering on it, on the Moome card. I think the goal is to have as little as possible touching the video chain. Now that you have DC coupled the only thing in the chain is the first two relays, a buffer amp (opamp with DC restore), an analog switch (internal vs. external video), and the Gain control (Multipliers). My guess would be that the next weakest link would be the analog switch.

As for me trying this mod, I can’t, I don’t even have an internal Moome card. But I thought I would try to follow through with a recommendation for a relay that would work.

[Nashou66]

Yes the SD5401 switch, is this the one your talking about? I have data sheets on it but they have no mention of bandwidth. it has to be at least 120Mhz as i think this is the rated frequency for the projector in its stock form. But i would still like to know what that number actually is. All my emails to Linear Technologies about that chip have gone unanswered. they are the company that now makes them...they make obsolete older out of production parts of other companies.
Jeahong lee bypassed this switch and said the picture did improve however he lost the internal video. I was trying to think of a way to bypass the video around that chip and then somehow maybe add the internal video directly to the video output amps or the mini rca's via a relay system like you came up with in this thread. It seems you have a better grasp about this than I do. do you think this is possible? bypass that chip. then take the output of the internal video from the sd5401 feed it to a relay that would either switch from external to internal or maybe do as some more modern displays do just add the internal to the external , sorta as an overlay. Or would this "mix in" the video making it scrambled or distort the internal patters and menu. And if a relay is used here as well would that also add another wink link to the video? Which would be worse the SD5401 or the relay? the one adding the less noise is what we want.

EDIT:
Ok here is a quick drawing i made showing the bypassing of the D5401 section that takes the external video. and a relay added that would switch between the internal and external. not sure if there is anything else involved that I am overlooking that would not allow this to work. Not a EE so someone else chime in. I would just have to figure out what signal to trigger it with.

EDIT:

Just realized this way I'd lose video during menu functions. I think the SD5401 sometimes shuts off external video or mutes it during any of the # key presses and other menu item that use the internal patterns and also overlays the menu over video for other uses, like contrast,brightness ect. i think there is a way but I'm not knowledgable enough to see it.



Athanasios

[9kids]

No a relay will not work in place of the SD5401. The Sd5401 is a pixel rate analog switch. In order to display a internal menu overlay on top of the external video, it actually has to be able to switch as fast as a pixel. What happens is, as the external video scans across on a single line the SD5401 has to switch to the internal video in the middle of the scanline in one pixel speed, display the internal video (menu) and then switch back to the external video to finish the line. There are very few analog switchs that are fast enough to do that. The SD5401 has a T-on time of 1ns, I think we could go as high as 10ns maybe even slower, the switching speed would only effect the qualty of the transitions from external video to internal and back again. So a switch that was a little to low in speed would make the left and right sides of the overlay menus look bad, but you could probable live with that. The next most inportant feature would be low noice. I really don't understand enough about all of the other specs on these analog switchs to know if one would be better than another. I just got a grip on the T-on and T-off speed thing so far.

[Nashou66]

yeah I went back and read the old archive posts. do you think we might be able to get away with 17ns? this might be a good alternative:

http://focus.ti.com/lit/ds/symlink/ts5a4596.pdf

Athanasios

[1031]

[Nashou66]

[1031]

I "lifted up" pins 11 & 14 and routed signal trough that videoswitch.

[WTS]

There are no pixels in a crt!

[Nashou66]

[1031]

And if you look closer, i corrected my mistake.

[9kids]

[Nashou66]

1031 saiys that chip also controls blanking, i dont think this is true unless i was reading the manual wrong. that is only a switch that switches between external and internal depending on what the signal it is sent from the 74AC74 D type flip flop . two signals that are 180o out of phase V-SEL and V-SEL*.Taken from the manual:::When the input (INT/EXT*) is low, V-SEL is set high to swithch to internal video and when (INT/EXT*) is high, V-SEL* is high and switches the internal video. So there is no blanking here just switching when a signal comes from that flip flop chip that sends a signal when an internal video needs to be sent to the output amp, along with video from the internal video op -amp. So if i am thinking correctly, video from both internal op amp and external video are sent at the same time to the RGB rca's then to the VNB. Thus having the overlayed menue video over the external source video. remeber that the internal video is generated on the CLM.

Athanasios

[1031]

I´m not sayig that it controls blanking, no no.. Clm is contolling it.
Anyway, i just remember that when i tested that bypassing there was blanking issues. i´m not 100% sure was that blankig done at neckboards or was it related to that sd5401 chip.

[Nashou66]

Ok Jarmo, I knew you were too smart for that ! So we know that the sd5401 is a week link and we need an equally fast switching chip with a
known bandwidth and less noisy than the sd5401 . After reading the service manual it also says that the SD5401 switches in 1ns which is difinitely faster than any other chip I have seen, so maybe eliminating this section of the chip is out of the question unless there is a way to still use a relay where the signal before the sd5401 is split and will go to the relay around the chip while video is being watched and then the output from the sd5401 also goes into the relay so when internal video signal is detected the relay would switch the that so it can be used to make adjustments and soforth, then once the adjustments are made and the internal video signal is shut off the relay switches bac to using the bypassed signal. No? Just trying to get you guys thinking, and maybe I'll learn more along the way !

Athanasios

[9kids]

Ok here is how I think it all works.

[Nashou66]

Here is a photo of the internals of the SD5401 i dont have a scaner home. this was sent to me by Linear systems.Maybe this can help. 9kids you might have to redraw your diagram to change the switch it looks close.Trying to figure out the S,D, and G also the substrate.
D=signal in
S=signal out
G=either V-SEL or V-SEL* or INT-Clamp or CLAMP depending on section of SD5401this makes the connection
Substrate ? could this be ground?I do not see any place on the schematics that show's the connection of pin 2(substrate) on the calogic spec sheet for same SD5401 they call it Body not substrate.
I think this keeps the switch open(no connection).
When any of the G signals are present the connection is made so any of the three or any combination of the sections can be sending a signal through the chip at the same time, that is to the dc restor circuit TL071's/TLO82's and from the video op amps internal/external to the rca jacks. so the sd5401 does not mix signals internaly it only routes the appropriate signal to their respective circuits depending on what the flip flop chip or clm tells it to do.

What do you guys think?









If you look at this section you can see that the internal and external connect to a common lead that goes directly to the RCA jack, does this mean that the sd5401 allows two seperate signals to be output over the same transmission line, thus becoming an overlay of video to the VNB. If so then a relay can be used near the sd5401 where the signal can be taken before pin 11 route it to the relay. when internal video is selected we also send that signal to the relay to trigger it to switch to input to pin 11 if no signal is present for internal video or the signal is present for external the relay switches so the video signal is routed around pin 11 and sent to the trasmission line on its way to the AD834 where contrast is added, then it makes its way to the output amp to the rca jacks.







Athanasios