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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Mon Feb 02, 2009 3:34 pm Post subject: BG808: changing caps for better video signal ? |
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Hi,
I know that there are different topics talking about it, but I didn't read any definitive answer.
So I am looking to improve the PQ of my BG808 (especially sharpness) and I was wondering if changing caps (by Panasonic FC for example) on the following boards, can make a difference : R7621055 and R7617481 (used for port 3).
Has anybody done that?
Cheers
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perisoft
Joined: 29 Aug 2007 Posts: 2920 Location: Ithaca, NY
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Link Posted: Mon Feb 02, 2009 4:06 pm Post subject: |
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I haven't, but my understanding of the 808 (particularly the non-s) is that the tubes are more of a limiting factor for sharpness than the electronics - ie, the electronics can paint a sharper picture on the phosphor than the phosphor can resolve.
If the caps have deteriorated, I guess it could make a difference, but as far as I know with an 808s (with sony tubes) you're maxing out the tubes' resolving power by the time you get to the point where the electronics are an issue.
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Mon Feb 02, 2009 4:20 pm Post subject: |
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I am sure there is a possibility of improvement when you see all the mods available (Mike Parker, Greg Eisemann,...)
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perisoft
Joined: 29 Aug 2007 Posts: 2920 Location: Ithaca, NY
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Link Posted: Mon Feb 02, 2009 4:49 pm Post subject: |
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Corleone88 wrote: | I am sure there is a possibility of improvement when you see all the mods available (Mike Parker, Greg Eisemann,...) |
Yes, but Eisemann sells high-res tubes so you can see the difference the other mods provide.
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Wed Feb 04, 2009 8:41 am Post subject: |
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Nobody tried changing caps on these boards ?
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Ile
Joined: 09 Mar 2006 Posts: 1491 Location: Jyväskylä, Finland
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Link Posted: Wed Feb 04, 2009 9:25 am Post subject: |
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If input boards are high hour you might see some difference by chancing bipolar elcaps from input boards.
http://gallery.avsforum.com/showgallery.php/cat/500/ppuser/7428372
Chancing caps won't make picture sharper, there is needed to chance also transistors and modify peaking circuits etc. That is very time consuming and good test equipments is needed.
Modifying boards power lines filtering using bigger caps and inductors can make noise level lower. This is already done to 808s input board in factory.
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Z-Photo
Joined: 07 Mar 2006 Posts: 2753 Location: Huntsville - Alabama
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Link Posted: Fri Feb 06, 2009 11:04 am Post subject: |
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I focused on the video amp boards and the SMPS.
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Fri Feb 06, 2009 7:45 pm Post subject: |
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What did you change exactly in the video amp boards ? What were the results on the picture ?
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kal Forum Administrator
Joined: 06 Mar 2006 Posts: 17860 Location: Ottawa, Canada
TV/Projector: JVC DLA-NZ7
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Link Posted: Mon Feb 09, 2009 1:14 am Post subject: |
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I changed a few hundred caps in my old BG800 that had about 24,000 hours on it at the time. Changing the bipolar's in the video input card did wonders for the colours. It was like a grey veil was lifted. The colours were considerably better. Didn't have a colorimeter at the time but it would have been interesting to measure the before & after primaries.
Changing the other caps (mostly the big SMPS ones) greatly improved convergence stability but it did nothing for the image quality/sharpness. In fact, caps won't help your sharpness.
Kal
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Tue Jun 30, 2009 8:16 am Post subject: |
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I update this topics because I recently calibrated my BG808. Colors are nice, sharpness is OK, but I see some noise in the picture (1080i/24 with Lumagen HDQ + BD35 + BJC + HDFury1). So I am planning to buy used R7621055 and R7617481 boards and change the caps (with Panasonic FC) in order to reduce the noise. Is this worth it ?
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akajester
Joined: 09 Jul 2008 Posts: 934 Location: Wisconsin
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Link Posted: Tue Jun 30, 2009 12:25 pm Post subject: |
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I screwed up one of my input boards doing that. I guess I'm just not good enough at changing caps. Only do a few at a time, and test test test!
I guess the results will depend on how bad your previous caps were. My unit has 5000+ hours on it, so not too bad. Kal had like 20k+ so it made a big difference for him.
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WTS
Joined: 08 Mar 2006 Posts: 1276 Location: Calgary
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Link Posted: Tue Jun 30, 2009 12:56 pm Post subject: |
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Changing the input caps won't help the noise problem but changing the PS caps on the 2 boards might. DOn't worry about screwing up the caps, just remember to get them in polarity correct. You can go a little larger in value but try to stay close to the same voltage ratings.
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Tue Jun 30, 2009 1:14 pm Post subject: |
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What are the PS caps?
What is the use of the caps on the video input boards?
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akajester
Joined: 09 Jul 2008 Posts: 934 Location: Wisconsin
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Link Posted: Tue Jun 30, 2009 1:32 pm Post subject: |
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Corleone88 wrote: | What are the PS caps?
What is the use of the caps on the video input boards? |
I had heard that when the caps get old on the video input board it can dull your colors. Not sure if it's true and never went back to try and repair the board to find out.
Are the PS caps the power supply caps? You can find a service bulletin about that on Curts site.
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Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Tue Jun 30, 2009 2:04 pm Post subject: |
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Athanasios,
After changing the PS caps, have you seen less noise in the picture?
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Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
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Corleone88
Joined: 09 Dec 2006 Posts: 448 Location: France
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Link Posted: Tue Jun 30, 2009 2:26 pm Post subject: |
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How many hours on your Marquee?
My BG808 has around 12000 hours.
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Nashou66
Joined: 12 Jan 2007 Posts: 16171 Location: West Seneca NY
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1031
Joined: 22 Mar 2006 Posts: 657 Location: Finland
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Link Posted: Wed Jul 01, 2009 8:35 am Post subject: |
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Those bipolar caps that are series on rgb-lines usually are for blocking dc voltages between video stages. Ok, they work pretty good in theory. There are lines that are terminated to 75 ohm (or something else) and usually there is series resistor ( ie. 75 ohm ) and before/after there is cap (bipolar or normal ) Now caps impedance comes to play. Good cap has low impedance and that doesn't change much lines total impedance (75+ caps internal impedance) Old bipolar can have impedance near 10 Ohm at certain freq. And that cause poor impedance match between video stage´s. Good cap should have small impedance at wide freq.range, then it is good for circuits like that are used in barcos/sonys.
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Last edited by 1031 on Wed Jul 01, 2009 11:23 am; edited 1 time in total
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