CurtPalme.com Home Theater Forum

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Hi Everybody,

I did the following mod to my VIM:

http://www.curtpalme.com/docs/ElectrohomeMarqueeTechnicalBulletin_LineFix.pdf

Now I have the impression that after this mod the blacklevels have to be adjusted and the image has much less contrast.

I did a color correction (G2 and drive settings with internal signals) and i looks better but still duller that before the modification.

The faint vertical line near the right side of the image has dissappeared.

Could this be just imagination (I forgot to look at the image before doing the mod) or did I do something wrong.

I've double checked everything and it should be OK I've put the resistors on the component side instead but I guess that shouldn't matter. I've used a 1M and 520K 1/4watt resistor in series instead of the 1/8 watt 1M5 that was recommended

I've put a picture of my mod.

What is your opinion about that.

Regards,

Ron

draganm · Joined: 08 Mar 2006 Posts: 5080 Location: Colorado

First off it looks a bird pooped on your board Laughing

I'm joking, my only thought is your running resistors directly over some delicate chips which might not like having a resistor sitting on top of them. If the factory engineers instructed to put the resistors on the back-side there's almost certainly a reason for it.
Other than that that this modification raises Brightness level significantly, that's normal. Where on a stock marquee you might run Brightness 40 to 45 after the mod I found good Black levels come in at 10 to 20. I also took down the Brightness in my BD player a little as well. IMO, the shadow detail and full fade to black on my marquee are very good.

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Thanks Draganm,

In the mod one of the resistors is actually on the component side.

I put everything on the component side because there is the ground backplane that's very close to the soldering points and I din't want to make a short to ground.

I also have the impression that the image was less sharp but in order to do the mod I had to move the projector back and forward (it's on a table with wheels until i mount it on the ceiling) and the focus could be different. It could also be blooming since the brightness is no higher

Thanks for your answer.

Regards,

Ron.

draganm · Joined: 08 Mar 2006 Posts: 5080 Location: Colorado

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Thanks again,

I'll do some testing during the weekend.

For your info its a 1100 hours machine (tubes and chassis) from 1995 with red and green C elements.

Regards,

Ron.

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Hi everybody,

I'm still puzzled with this mod.
(I've done a noise reducing mod on the LVPS that was very successful in the meantime to reassure myself that I'm capable of doing something right.)

I now have a fresh look at it and I wonder if this mod is for my board. My board is labeled "50-2035-02P iss.2" but in the doc they talk about Video input modules 02-270335-02P through 05P

I have also changed the "bird pooped construction" in something according to the tech field bulletin but that doesn't give any improvement.

I have adjusted the G2 and DRIVE settings with internal signals but have not checked that with an external test pattern.

I have the feeling that I'm heavily overdrive the tubes.

When I start up the cold projector the image is actually good but it becomes a bit less sharp and a bit washed out after a few minutes.

What I also noticed is that when i view a scene with a black background and white text that when the text disappears i can still see this text but now in black blacker than the black background. Even when another white text appears I can still see this first text in black overwritten by the new white text. This black text stays there for at least 8 to 10 seconds. Is this normal remanence of the tube or is it because i drive it too hard?

I hope I made myself clear.

I'm really considering undoing the mod and live with the faint line.

Can anybody comment on this?

Nashou66 · Posted: Wed Apr 25, 2012 11:37 pm Post subject:

Undo the mod on the green tube to see if it fixes the brightness issue. if so undo the mod. Are you sure you have the correct resistor value?

Athanasios

mp20748 · Posted: Thu Apr 26, 2012 1:21 am Post subject:

Try three 2.2 meg resistors instead. That's what I have used in the past that works best for the video you'll be using.

The resistor mod corrects a pedestal problem caused from the internal generator on the control board. It's a good fix, but it also causes the image to be washed out even when properly applied. The problem it also creates is that you'll actually loose the input signals true black level.

Two things are happening at the same time and that's why the line is present:

1, The control board has its internal generators pedestal (black level) active even when the generator is not being used.

2, The input signals pedestal is being crushed or over taking by the constant pedestal from the internal generator.

A better fix for this would be to have a calibrated pedestal level from the internal generator that could be aligned/matched to the pedestal level of the input signals clamp circuit pedestal level. Meaning that you would be able to have one black level reference for both sources (internal generator/input source) instead of two operating at different reference levels.

I've also solved this from the control board, which is what I use today. I had planned to send this procedure to Tim along with a few other tweaks, but have not got around to it. When done, the line is gone, and there would be only one pedestal, that would be from the source only. And the internal signal generator will still be active, but with-out its pedestal creating a problem for the source signal.

The 2.2 meg should get you closer, but it would not be the best and most accurate fix. You could also play around with different values and see which provides the best fix.

stridsvognen · Posted: Thu Apr 26, 2012 6:34 am Post subject:

That explains why i'm still messing around to find the nice black level and clearness i saw some time ago, but i have way to much going on here, so thought it was just me doing something wrong.

a better solution will be very apreciated from here.

stridsvognen · Posted: Thu Apr 26, 2012 7:46 am Post subject:

I just testet the mod vs. No mod, and when calibrated with the mod, i have brightness to 50, and with the same settings i needet to put brightness to 85 to get the same average gamma in the dark levels.

my settings with the mod is like this.

DVDO TEST PATTERN

DVDO Gamma 1.1 PC level 0-255 HD Furry 3

WHITE LEVEL = USER SETTING
RD 17
R G2 67

GD 60
G G2 66

BD 21
B G2 67

Brightness 50
Contrast 66

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Thanks everybody,

I'll have a look on the schematic to see what can be done.

Maybe we can introduce in the signal path some negative black level (fooling the dc restoration circuit) that then will be cancelled out by the mod further on.

At the end the mod is just a fix for the symptom but not for the real problem.

I'll keep you informed.

Ron.

ronaldus · Joined: 25 Dec 2010 Posts: 105 Location: france

Hi everybody again,

I had a look at the schematic of the VIM and to select between the internal and external signals a mosfet solid state switch is used. maybe this switch (SD5401 U25) is the cause of the crosstalk. What I would like to try is to take the V-SEL control signal and feed it to a Mosfet that shortens the INT VID signal on R173 connected to U16. Then there would be no internal video present when the external video is used.

The best would be to replace this SD5401 with a relay.

I think its worth a try.

I'll check it out.

Ron.

draganm · Joined: 08 Mar 2006 Posts: 5080 Location: Colorado

Nashou66 · Posted: Thu Apr 26, 2012 4:52 pm Post subject:

Removing SD5401 will have you loose all menus. Changing it you will have to have it be a fast switching switch or as fast as the SD5401. it can be done but most have found more noise is added. Best is to just use a VP that has gamma correction and leave the mod as is.

Or play with the DC restore resistor near the TLO71, i forgot which one.

But for me using a Lumagen and lowering the Luma(Gamma) at 0IRE to below Zero did the trick. Too bad the DVDO doesn't have Gamma correction.

Athanasios

stridsvognen · Posted: Thu Apr 26, 2012 5:02 pm Post subject:

New settings. without mod.

RD 21
R G2 70

GD 80
G G2 70

BD 26
B G2 69

contrast 68
brightness 60

Don't know if i'm just to careful, but should i calibrate with the G drive at 90.? what i seen Don't look like it changes much after 80

Notice i have the gamma set to 1,1 in my vp50 its lowering the gamma

Nashou66 · Posted: Thu Apr 26, 2012 5:08 pm Post subject:

keep brightness and contrast at 50 for both when doing greyscale.

Athanansios

mp20748 · Posted: Thu Apr 26, 2012 5:24 pm Post subject:

You cannot correct this problem using the MOD with an external processor. With an elevated pedestal, not only is the black reference off, so is everything else with modern HDTV sources, and that includes the colors.

The resistor MOD is the pedestal adjustment resistors. Its just that the MOD may work well for SDTV, but for converted Component Digital HDTV signals of today, the better the pedestal reference, the better the image. And that's why the earlier version Transcoders and HDMI/DVI converters had color space problems (low level, crush, peak white).

Try this... at the point of where the three resistors tie together, put a pot from there to the B+ reference point that the resistors were removed from. And it would be best to use a pot that you could also mount in one of the RCA connector (for audio) holes. And that would allow you to adjust the pedestal from the plate on the VIM.

Later today when I get back, I'll attach the pot as I described above on one of my 02 VIM's and post pictures of it.

macgyver655 · Joined: 22 Aug 2007 Posts: 6953

Or just buy an AMPRO, and avoid all these "Marq" problems......... Laughing

Hey, I haven't barked an ampro plug in a long time.....lol

stridsvognen · Posted: Thu Apr 26, 2012 7:13 pm Post subject:

Ron, i'm happy you got this issue to my attention, i did this mod 1 week ago, and sure i noticed some changes, but i was to busy trying my new HD Fury and different other way of connecting.
i spent lots of time looking for my lost black.. was sure it was just me that was a fool, not knowing up and down this machine.

Now removing the mod, ill for sure say that the returning black is worth more than getting the line away.

So for now i think ill just wait and see who finds a better solution.

Nashou66 · Posted: Thu Apr 26, 2012 7:20 pm Post subject:

Well Mike my machine does not have the raised black issue with the mod done from the factory. But still doing greyscale with a VP and lowering 0 IRe does wonders for how soon it comes out of black. Not all color tubes are linear and trying to match all three coming equally out of black linearly to 10 % white level is very difficult . That is the area where shadow detail makes the image look 3D. using a VP in this manner is the best way to deal with black level and shadow detail.

Athanasios