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NEC XG picture width at 1080p, possible solution?

 
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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Thu Apr 21, 2016 5:10 pm    Post subject: NEC XG picture width at 1080p, possible solution? Reply with quote


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A well known issue of the NEC XG projectors is that they do not like the today's standard timing of 1080P 60Hz signal (2200 pixels total width). This is because of the high blanking time of the XG deflection circuit.
Silmilarly to the Marquee projectors the XG also have multiple retrace times over the scan frequency range, but unlike to the Marquee the XG does not let any user intervention to this retrace time control, it is carried out fully automatically -unfortunately.
Normally alternating the retrace time would involve heavy modifications around the deflection circuit, that could be expensive and time consuming.
So I come up with a different approach. Looking at the XG135 specifications we see the following regarding retrace times:
15-30kHz: 6us
30-77kHz: 2.6us
77-120kHz: 2us
120-135kHz: 1.4us

These are retrace times, for real signals the blanking time is important (which is unpublished) but is always bigger than the actual retrace time.

The standard 1080P 60Hz signal has about 67kHz scanrate, and has a blanking time of 1.9us.

I did a small test on my XG135 and got the following results for (real) blanking times:
15-30kHz: did not test
30-77kHz: ~3.5us
77-120kHz: ~2.5us
120-135kHz: ~1.7us

It's clear to see that our only hope is the last range, because otherwise it could not meet the blanking time of the input signal.
The retrace time is altered by setting of the deflection yokes into series or parallel operation, and by switching on and off certain resonant capacitors.

Switching the resonant capacitors make no big deal it can be switched without danger, and in fact in the Marquee this is a user selectable feature. What is a bit more problematic is: the deflection yoke configuration switching. Normally with XG this is switched over from series operation to parallel at 77kHz. If the yokes configured to parallel at low scanrates the dissipation would be unnecessarily high on the DEF board.
Fortunately our target is 67kHz which is not far from 77kHz, so this wouldn't be a real problem. For example the Marquee deflection board work in a similar way, but the switching is made at only 60kHz.
So the basic idea is to modify the OSC board (where the retrace control signals are originated) that over a certain scan frequency (say 60-65kHz) it would be forced to operate in the 1.4us retrace mode. Below that the opration would be as originally.

Good news is this feature is not limited to XG135 models only, because ALL XGs employed the same H-DEF board, so every board has all the features to go to 1.4us retrace time, it is just the scanrate that is limited (by software) with the different versions.

Who's interested?

_________________
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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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Sun Aug 21, 2016 1:37 pm    Post subject: Reply with quote

Today I revisited this topic, and I built a simple add-on circuit to the OSC board that forces to use the 1.4us retrace range above 61kHz scan rate. The idea works, so I managed to stay within raster with the picture using standard 1080p 60Hz timing (2200 total pixels horizontally). In return the H-DEF board gets significantly warmer, I'd even say it is hot, so I have to see if the stresses remain specs on that board, but at least the theory works indeed.
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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
The MOD: VNB-DB
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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Sun Aug 21, 2016 4:39 pm    Post subject: Reply with quote

As it seems in this "override" mode the H-DEF board produces roughly the same heat as at 1080P 72Hz in normal mode.
So if someone wants to try this I can reveal how I did, it only need two resistors and one opamp and some wires.

_________________
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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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Mon Feb 06, 2017 8:59 pm    Post subject: Reply with quote

Here you can find the scematic diagram of the modification in question.



It needs cutting one trace, otherwise it can be installed on the OSC board without much intervention. The OSC boards were slightly different over the three generations, but this mod applies to all except for the source opam has different refence designator, as seen on my drawing.

This modification enables the shortest retrace time mode in the ~60-75kHz scan range, this way it is possible to display 1080P with stock timings without cropping the image. Outside this range the retrace time is the same as before.

One note. With this mod it is expected to run the bords slightly warmer because the retrace time is a dead time for "relaxing" to the circuits, so being the relaxing time less it generates more heat, but as long raster is not too wide and the general setup was made with care it should be OK.

_________________
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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dummyload



Joined: 06 Apr 2006
Posts: 37
Location: belgium


PostLink    Posted: Sun Feb 12, 2017 4:07 pm    Post subject: Reply with quote

Very wel done , nice work.
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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Sun Feb 12, 2017 4:50 pm    Post subject: Reply with quote

Thanks, 10years ago this could have been a hot topic, today you can count on one hand who use an XG. It was fun to find out if it can be done though.
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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
The MOD: VNB-DB
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dummyload



Joined: 06 Apr 2006
Posts: 37
Location: belgium


PostLink    Posted: Sun Feb 12, 2017 7:54 pm    Post subject: Reply with quote

It sure would have been and yes fun it is.
The demise of crt is sad great technologie ,I fell in love with it about halfway the 80's when I got responsible at my work for the maintenance of a barco vision 2 in a local discotheek many years later in 2001 I got my own first crt projector a barco vision (one of the first models they made 1981) from there I whent trough a dozen entry level projectors from different manufacturers over the years until a few years back thanks to the demise I could acquire a dead cinemax and later a dead barco 919 so I'm glad I have the change to learn and playing with it's electronics . I have to admit though I stil haven't done a thorough setup yet (shame on me) ,stil more busy with the inside then watching movies and the lack of time ofcourse.
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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Sun Feb 12, 2017 8:06 pm    Post subject: Reply with quote

I am a sort of late commer (2010) to the CRT scene,, but to my excuse I was only born in 1987. Smile
These days with having a 2 month old son I don't really find time for watching movies anymore, in fact I think it was last september when I saw a full movie. The little spare time I have these days, mostly spend with the VNB-DB boards Smile

_________________
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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gregstv



Joined: 27 Aug 2007
Posts: 626
Location: Australia


PostLink    Posted: Mon Feb 13, 2017 8:59 am    Post subject: Reply with quote

I had finished my trade certificate for television repair before you were even thought about. Now I feel old.
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dummyload



Joined: 06 Apr 2006
Posts: 37
Location: belgium


PostLink    Posted: Mon Feb 13, 2017 6:59 pm    Post subject: Reply with quote

Yeah was thinking the same ,we better start to develop a board that reverse time it has been running for far to long in the same direction by now ,maybe ad834 and ad8009 wil come in handy.(lol)
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benareeno



Joined: 22 Mar 2006
Posts: 1614
Location: ottawa, canada


PostLink    Posted: Thu Mar 23, 2017 6:23 am    Post subject: Reply with quote

the best thing you can do is NOT run 1080p on an XG....it's foolishness at best. 720p is still not fully resolvable, so why bother going beyond it?
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gjaky



Joined: 05 Jun 2010
Posts: 2650
Location: Budapest, Hungary


PostLink    Posted: Thu Mar 23, 2017 9:06 am    Post subject: Reply with quote

benareeno wrote:
the best thing you can do is NOT run 1080p on an XG....it's foolishness at best. 720p is still not fully resolvable, so why bother going beyond it?


At 720P I can see the scanlines on mine, but yes 1080P can't be fully resolved, although there are circumstances where it is more desired to have an "optical scaling" rather than digital scaling down to 720P. Since I use HTPC as source I run 1080i 96Hz to my XG. This thread is to show an interesting oportunity...

_________________
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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