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BG808: changing caps for better video signal ?
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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Wed Jul 01, 2009 10:04 am    Post subject: Reply with quote


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Thanks, that is very interesting Very Happy.
When you said that at 75 Ohms the circuits work better, what does it mean exactly ? The video signal going through them, would be cleaner ?
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1031




Joined: 22 Mar 2006
Posts: 657
Location: Finland


PostLink    Posted: Wed Jul 01, 2009 11:21 am    Post subject: Reply with quote

Those video lines are not always matched to 75 ohm (on circuitboard, there can be different terminations ie. 50 ohm )
But when cap. between two impedancematched stages gets old (and it´s internal impedance starts to rise) it can create impedance mismatch, that lower picture quality. (signal starts to reflect between two stages)

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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Wed Jul 01, 2009 12:21 pm    Post subject: Reply with quote

What are usually the number of hours of use before caps begin to increase their impedance?

If I say that mine have 12 000 hours, do you think it is the time to change Wink ?
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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Wed Jul 01, 2009 12:22 pm    Post subject: Reply with quote

What are usually the number of hours of use before caps begin to increase their impedance?

If I say that mine have 12 000 hours, do you think it is the time to change Wink ?
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Nashou66




Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY


PostLink    Posted: Wed Jul 01, 2009 1:16 pm    Post subject: Reply with quote

Oh yes 12000 hours is a lot. Just look at the specs for some caps. they are rated at the hours for the max temperature but even at low temps they would be very aged at the 12k hour mark, also just sitting on a shelf caps can degrade.

Athanasios

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1031




Joined: 22 Mar 2006
Posts: 657
Location: Finland


PostLink    Posted: Wed Jul 01, 2009 1:17 pm    Post subject: Reply with quote

Corleone88 wrote:
What are usually the number of hours of use before caps begin to increase their impedance?

If I say that mine have 12 000 hours, do you think it is the time to change Wink ?


That depends where/whatkind of circuit cap is used, and also how good quality cap was in first place
But with those hours, change those bipolars and see if you notice any improvement in picture quality Smile

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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Wed Jul 01, 2009 1:36 pm    Post subject: Reply with quote

Ok. I will start with the big caps on the Power Supply, all the caps of th RGB switcher and RGB analog input boards.
What are the other boards which would have an influence on the picture quality ?
What about the 3 video amp boards?
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draganm




Joined: 08 Mar 2006
Posts: 8990
Location: Colorado


PostLink    Posted: Wed Jul 01, 2009 4:38 pm    Post subject: Reply with quote

Corleone88 wrote:
What about the 3 video amp boards?
Absolutely, you will see a sharpness increase, color saturation, less noise (snow), etc.
A cap doesn't go bad from just high run hours, they dry out from just sitting ion the shelf. That's why they have a date-code on them. IT's like canned vegetables, they don't last forever. Laughing
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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Thu Jul 02, 2009 9:30 am    Post subject: Reply with quote

Does the caps voltage needs to be exactly the same for a replacement?
I have for example 100microF 25V to replace 100microF 16V and 470microF 35V to replace by 470microF 16V?
Is it OK?
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Ile




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


PostLink    Posted: Thu Jul 02, 2009 10:58 am    Post subject: Reply with quote

Corleone88 wrote:
Does the caps voltage needs to be exactly the same for a replacement?
I have for example 100microF 25V to replace 100microF 16V and 470microF 35V to replace by 470microF 16V?
Is it OK?
Yes, it's ok.

For input bipolars you can also try small plastic caps (0.1-1uF) in parallel with el-bipolars, those should help with high freq signals.
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Nashou66




Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY


PostLink    Posted: Thu Jul 02, 2009 11:57 am    Post subject: Reply with quote

Ile wrote:
Corleone88 wrote:
Does the caps voltage needs to be exactly the same for a replacement?
I have for example 100microF 25V to replace 100microF 16V and 470microF 35V to replace by 470microF 16V?
Is it OK?
Yes, it's ok.

For input bipolars you can also try small plastic caps (0.1-1uF) in parallel with el-bipolars, those should help with high freq signals.


these would work great:

http://www.mouser.com/Search/ProductDetail.aspx?qs=IKkN%2f947nfD8ohpReLZe4A%3d%3d

http://www.mouser.com/Search/ProductDetail.aspx?qs=H7Zs1csUUyicHJGe42DNww%3d%3d

Athanasios

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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Thu Jul 02, 2009 3:54 pm    Post subject: Reply with quote

What are input bipolars? The electrolytic caps on the port 3 RGB board?
What are el-bipolars?
Is 40KHz (1080i@72Hz) a high frequency Wink?
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1031




Joined: 22 Mar 2006
Posts: 657
Location: Finland


PostLink    Posted: Thu Jul 02, 2009 4:51 pm    Post subject: Reply with quote

Corleone88 wrote:
What are input bipolars? The electrolytic caps on the port 3 RGB board?
What are el-bipolars?
Is 40KHz (1080i@72Hz) a high frequency Wink?


Bipolar is electrolytic cap that has no polarity, normal cap has minus pole marked..
EL-> electrolytic (cap has electrolytic fluid in it)
40Khz->horisontal scan freq. Actual videoinformation at those resolutions is much higher, Megaherz range.
Search bandwith for more info.

_________________
Marquee 9500LC (Frankenyokes / Thomas electric tubes / HD-10L / +many mod´s)
DVDO VP-50
New hobby, Rally
http://www.youtube.com/watch?v=vX2Rtpr1njs
http://www.youtube.com/watch?v=6ZP9FEFXV5c
http://www.youtube.com/watch?v=j065vei6j6s
http://www.facebook.com/pages/JTS-Racing-team/204443719572685
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Corleone88




Joined: 09 Dec 2006
Posts: 443
Location: France


PostLink    Posted: Thu Jul 02, 2009 6:29 pm    Post subject: Reply with quote

Ok thanks. But where are the input bipolars?
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