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Barco 120MHz neck board streaking

 
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Wed Nov 07, 2012 5:30 am    Post subject: Barco 120MHz neck board streaking Reply with quote


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I have the 762721 boards with Sony tubes in my BG808s and 1 of the 3 is streaking. I swapped boards and the problem follows this one board so I'm certain.

I thought these boards had the high speed parts that wouldn't streak. Not sure what chip to look for ... There is SK6 357 on this one and the other two have slightly different numbers. Or maybe it's just bad.

I'm running it at 67.7kHz if that matters.

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AVStefan
HDFury3 -> BG-808s + HD-145 lenses.
HDFury2 -> Pioneer 533 RPTV
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gjaky



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


PostLink    Posted: Wed Nov 07, 2012 6:45 am    Post subject: Reply with quote

Once I had a streaking issue with my NEC and it was a timing issue, not sure, but you might try different timings, maybe one of your neckboard is hyper sensitive.
Also I think streaking is not a bandwidth related thing, it is a "clamping" issue, which could be due to a deffective part or bad construction.

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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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Decibel



Joined: 31 May 2007
Posts: 902
Location: Roma - Italia


PostLink    Posted: Wed Nov 07, 2012 9:03 am    Post subject: Reply with quote

R762721 is very common board.
I think that Curt certainly have a lot of these boards.
I suggest to buy a set for spare.
The board have two section: the PCB are tube's related (different by tube's type).

R762721 = Sony 8"
R762746 = Panasonic 8"
R762839 = Panasonic 9"

The other section (with black heatsink) instead is common at different types of PCB and have video chip Sanyo VPH08 or VPJ08.

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Domenico (Barco fan!)
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Ile



Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland


PostLink    Posted: Wed Nov 07, 2012 10:13 am    Post subject: Reply with quote

Probably some chip is going bad or someone have messed calibration from trimpots.

If it's chip related I guess it's bad Sanyo VPH08/VPJ08 or something ABL related.
Used neck boards are pretty cheap, so it's probably not worth to try find -97 discontinued VPH08/VPJ08 that would cost shipped from Asia about same or bit less what used neck board.

I have sourced few VPJ08 years ago from korean forum member, but not really interested to sell. Wink
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Curt Palme
CRT Tech


Joined: 08 Mar 2006
Posts: 23729
Location: Langley, BC

TV/Projector: All of them!


PostLink    Posted: Wed Nov 07, 2012 2:29 pm    Post subject: Reply with quote

I've got buckets of them... (the boards, that is).
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Wed Nov 07, 2012 3:02 pm    Post subject: Reply with quote

Ile wrote:
Probably some chip is going bad or someone have messed calibration from trimpots.


Curt Palme wrote:
I've got buckets of them...



Is it possible to get a set that is matched in case someone has messed up the trimpots or the boards are different vintage? The set has always been difficult to calibrate. I tried many different ways to set G2 with bizarre results. Using the menu controls I run out of adjustment range before achieving a good greyscale.

Thank you.
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Wed Nov 07, 2012 9:11 pm    Post subject: Reply with quote

Can they be matched for gain and bias?
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AVStefan
HDFury3 -> BG-808s + HD-145 lenses.
HDFury2 -> Pioneer 533 RPTV
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Ile



Joined: 09 Mar 2006
Posts: 1491
Location: Jyväskylä, Finland


PostLink    Posted: Thu Nov 08, 2012 8:58 am    Post subject: Reply with quote

Amps 200V line, gain (2.35Vpp/100Vpp) and ABL led are calibrated same way.
Pots are locked with varnish in factory, so if varnish are intact those should be pretty close even after 15 years.

ABL led adjustment tend to drift bit though.
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Thu Nov 08, 2012 3:05 pm    Post subject: Reply with quote

I guess I should not obsess over it and just replace the streaking board, as long as part numbers match. Any idea what R762721-02 is all about?
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AVStefan
HDFury3 -> BG-808s + HD-145 lenses.
HDFury2 -> Pioneer 533 RPTV
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Tue Nov 13, 2012 6:50 pm    Post subject: Reply with quote

Damn streaking! Twisted Evil

Watched The Hunt For Red October which is a dark movie and the nasty streaking appeared several times. Very distracting and aggravating after spending the time to upgrade to an 808, rebuild the failed power supply, and tweak it to almost perfect calibration.

Curt - I am one board away from true bliss... I hope you can find me a board in your parts bucket Sad
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AVphile



Joined: 02 Dec 2008
Posts: 316
Location: Ottawa, Ontario


PostLink    Posted: Tue Jan 15, 2013 5:18 pm    Post subject: Reply with quote

Ile wrote:
Amps 200V line, gain (2.35Vpp/100Vpp) and ABL led are calibrated same way.
Pots are locked with varnish in factory, so if varnish are intact those should be pretty close even after 15 years.

ABL led adjustment tend to drift bit though.


I had a few boards out on the bench and measured the pots... they are all over the map, no idea what's right. I realize the entire circuit needs to be considered, not just the pots... so does anyone have a procedure to calibrate them? I don't mind shipping them off somewhere!

The problem is my greyscale is still all over the place. I end up with R-CUT 99, G-GAIN 75, and drastically changing the R-MID & B-MID to get a 2-point greyscale but then gamma is rediculous 1.4 Thumbs Down

On the positive side, the streaking is gone Thumbs Up
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