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Moome Contrast Adjustment Process

 
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barclay66




Joined: 27 Jun 2011
Posts: 1259
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Fri Jul 17, 2015 3:17 pm    Post subject: Moome Contrast Adjustment Process Reply with quote


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Hi,

I just put this document together on how to correctly adjust the contrast potentiometer. Some parts of the text were "inspired" by posts on this site dealing with the same topic. I hope the original authors (I thing it's Craig mainly) won't feel offended...

Regards,
barclay66



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haireez




Joined: 14 Jun 2007
Posts: 202
Location: singapore

TV/Projector: Vidikron Vision 1 - Ultra


PostLink    Posted: Sun Jul 19, 2015 6:32 pm    Post subject: Reply with quote

What if some of us do not have oscilloscope? Can we do another method to reset it to original of 0.7 volts?
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barclay66




Joined: 27 Jun 2011
Posts: 1259
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Sun Jul 19, 2015 7:47 pm    Post subject: Reply with quote

Hi,

That will be quite difficult, but I will try to find some alternative. Maybe a small additional circuit that will produce a defined voltage (measurable with a conventional multimeter) when a specific input signal (picture content and resolution) is used. Let me work on that...

Regards,
barclay66
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gjaky




Joined: 05 Jun 2010
Posts: 2750
Location: Budapest, Hungary


PostLink    Posted: Mon Jul 20, 2015 6:58 am    Post subject: Reply with quote

barclay66 wrote:
Hi,

That will be quite difficult, but I will try to find some alternative. Maybe a small additional circuit that will produce a defined voltage (measurable with a conventional multimeter) when a specific input signal (picture content and resolution) is used. Let me work on that...

Regards,
barclay66


I think it can be done in two steps with a DMM:
1.) Show a full black pattern on full screen, check the output signal with a DMM and write down the value.
2.) Show a full white pattern on full screen, check the output signal again with the DMM, the difference should be 0,7V (ie. white level-black level = 0,7V)*

* Now I'm pretty sure there is a period in the output signal which is always black, due to the retrace, that might interfere with the DMM's sampling, resulting in unstable readings.
-> one should put a 100uF 10V capacitor between output (+) and ground (-) during the measurement.
-> use classical analog voltmeter (if you have one) instead of DMM, so you dont need the capacitor.

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projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
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barclay66




Joined: 27 Jun 2011
Posts: 1259
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Mon Jul 20, 2015 9:59 am    Post subject: Reply with quote

gjaky wrote:
* Now I'm pretty sure there is a period in the output signal which is always black, due to the retrace, that might interfere with the DMM's sampling, resulting in unstable readings.
-> one should put a 100uF 10V capacitor between output (+) and ground (-) during the measurement.
-> use classical analog voltmeter (if you have one) instead of DMM, so you dont need the capacitor.

Hi,

It should be a solution which works with different types and qualities of multimeters. Otherwise there are too many factors that could deliver erraneous results. A capacitor connected directly to the signal would simply kill it off as the capacitor represents something like a short for high frequency signals. There's even a chance that it could damage the corresponding video amplifier opamp.
I will try with a resistor (something in the 10-100K range) and a diode that charges a small capacitor (around 1F) so that I get a voltage without significantly influencing the signal. The diode will prevent any of the capacitor's charge to flow back onto the signal although its forward voltage drop will reduce the final voltage level (maybe putting several in parallel will work better). But it's not necessary to produce exactly 0.7V at its output. Any other reproducable result which represents a 0.7V pp video level will be sufficient...

Regards,
barclay66



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gjaky




Joined: 05 Jun 2010
Posts: 2750
Location: Budapest, Hungary


PostLink    Posted: Mon Jul 20, 2015 10:25 am    Post subject: Reply with quote

barclay66 wrote:

Hi,

It should be a solution which works with different types and qualities of multimeters. Otherwise there are too many factors that could deliver erraneous results. A capacitor connected directly to the signal would simply kill it off as the capacitor represents something like a short for high frequency signals. There's even a chance that it could damage the corresponding video amplifier opamp.
I will try with a resistor (something in the 10-100K range) and a diode that charges a small capacitor (around 1F) so that I get a voltage without significantly influencing the signal. The diode will prevent any of the capacitor's charge to flow back onto the signal although its forward voltage drop will reduce the final voltage level (maybe putting several in parallel will work better). But it's not necessary to produce exactly 0.7V at its output. Any other reproducable result which represents a 0.7V pp video level will be sufficient...

Regards,
barclay66


With a full white test pattern there isn't much high frequency signal, think of it as a ~99% duty square wave, which is smoothed by the capacitor. The video output should have 75 Ohm output impedance, that ensures the output even can be shorted...

For the series diode a schottky type could be a good choice, that still have 0.3V loss or so, which is temperature dependant, and even depend on the actual device somewhat. Without terminating the output the signal is twice as big, so there is some voltage to loose, but the reflections should be considered as a residual effect.

_________________
projectors in the past : NEC 6-9PG xtra, Electrohome Marquee 6-7500, NEC XG 1351 LC ( with super modified Electrohome VNB neckboard !!!)
current: VDC Marquee 9500LC
The MOD: VNB-DB
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barclay66




Joined: 27 Jun 2011
Posts: 1259
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Mon Jul 20, 2015 1:04 pm    Post subject: Reply with quote

Hi,
gjaky wrote:
The video output should have 75 Ohm output impedance, that ensures the output even can be shorted...

Possible. But we don't know which opamps Moome used on his cards (markings removed/replaced). So we don't know about their maximum allowed output current. 0.7V at 75 ohms result in 9.3mA. A CLC449 can deliver up to 80mA. Maybe the ones Moome used can deliver less. And if the output got "shorted" due to a large cap, there wouldn't be anything left for measuerement.

gjaky wrote:
With a full white test pattern there isn't much high frequency signal, think of it as a ~99% duty square wave, which is smoothed by the capacitor.

Yes. I had this type of test picture in mind as it produces the maximum output voltage over time.

gjaky wrote:
Without terminating the output the signal is twice as big, so there is some voltage to loose, but the reflections should be considered as a residual effect.

I think that this can be neglected as the signal is tapped only (therefore I would like to use a resistor with a higher value). It stays connected to the VIM's 2nd RGB input and is terminated with 75 ohms there...

Regards,
barclay66
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CIR Engineering




Joined: 25 Aug 2008
Posts: 4179
Location: Chicago USA & Berlin Germany

TV/Projector: JVC NX9 + Paladin DCR & Sony G90 : Lumagen Radiance Pro


PostLink    Posted: Mon Jul 20, 2015 1:29 pm    Post subject: Reply with quote

Good write up.

One suggestion though would be to get the green signal off the multipin connector rather than the resistor. Those members who don't normally do surface mount soldering will have an easier time adding the test lead and have less chance of damaging the board. You can connect to the pin on the underside of the board if it's inaccessible from the top. This will also protect again board solder fatigue.

Also, the easiest test pattern to use is a 100 IRE window. The 100 IRE window shows full 100 IRE (0.7 volt peak white) and full 0 IRE black. The difference on the oscilloscope between black and white should be set to 0.7 volts.

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
X-Rite i1Pro2 Spectroradiometer & Spyder Colorimeters for JVC auto-calibration
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion ColourSpace XPT Version β Color Calibration Software
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CIR Engineering




Joined: 25 Aug 2008
Posts: 4179
Location: Chicago USA & Berlin Germany

TV/Projector: JVC NX9 + Paladin DCR & Sony G90 : Lumagen Radiance Pro


PostLink    Posted: Mon Jul 20, 2015 1:35 pm    Post subject: Reply with quote

haireez wrote:
What if some of us do not have oscilloscope? Can we do another method to reset it to original of 0.7 volts?

One thing you can do if you have a colorimeter or spectroradiometer is to measure the light level of a 100 IRE window on the screen. If you keep your meter in the same place and at the same angle you can adjust your contrast up and down for testing and then you know about where to set it back based on light output from the projector. This is not as accurate as with a scope but it can work in a pinch. In the field when I don't have a scope I always measure peak white first so that if I accidentally turn the contrast knob I can get the contrast back to default.

Also, if you adjust gamma, your contrast will change a little. You can use that technique to adjust gamma and then restore contrast to the default value. If you try this, you should measure peak white with the gamma disabled first.

craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
X-Rite i1Pro2 Spectroradiometer & Spyder Colorimeters for JVC auto-calibration
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion ColourSpace XPT Version β Color Calibration Software
Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Authorized Dealer for Lumagen & just about everything worth buying Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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CIR Engineering




Joined: 25 Aug 2008
Posts: 4179
Location: Chicago USA & Berlin Germany

TV/Projector: JVC NX9 + Paladin DCR & Sony G90 : Lumagen Radiance Pro


PostLink    Posted: Mon Jul 20, 2015 1:42 pm    Post subject: Reply with quote

If you use a multi meter to adjust this, the best thing to do is take a voltage test reading of a 100 IRE white field before adjusting the contrast control. That becomes your baseline voltage. Then if you ever adjust the contrast control and need to get it back you can use the same white field pattern and set the contrast back to the same voltage.

Theoretically, anyone with a moome card here could take the measurement on any board and provide the number. With a true 100 IRE field the voltage should be the same on all cards. But that's only if the field is a full field and exactly 100 IRE.

Best
craigr

_________________
JETI Specbos 1211 Spectroradiometer
Photo Research PR-650 Spectroradiometer
Klein K10-A Laboratory Grade Colorimeter
X-Rite i1Pro2 Spectroradiometer & Spyder Colorimeters for JVC auto-calibration
Murideo Fresco SIX-G HDMI 2.x Multimedia Generator
Murideo Fresco SIX-A HDMI 2.x Analyzer
*NEW Light Illusion ColourSpace XPT Version β Color Calibration Software
Light Illusion LightSpace XPT Pro Version 10.x Color Calibration Software
Sencore CR7000 CRT Tube Analyzer / Rejuvenater
Authorized Dealer for Lumagen & just about everything worth buying Wink
www.CIR-Engineering.com - craigr@cir-engineering.com
Phone: 865-405-6892
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barclay66




Joined: 27 Jun 2011
Posts: 1259
Location: Germany

TV/Projector: Marquee 9500 Ultra


PostLink    Posted: Mon Jul 20, 2015 1:53 pm    Post subject: Reply with quote

CIR Engineering wrote:
One suggestion though would be to get the green signal off the multipin connector rather than the resistor. Those members who don't normally do surface mount soldering will have an easier time adding the test lead and have less chance of damaging the board. You can connect to the pin on the underside of the board if it's inaccessible from the top. This will also protect again board solder fatigue.

Thanks!

I will add this when I add the DMM measurement procedure...

Regards,
barclay66
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