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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Mon Oct 19, 2009 3:12 pm Post subject: |
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| Revox wrote: | Hi, i put some inductors of an old Motherboard in the +-15V and +-5V Line (don't know the Induktivity but might be better than nothing?) and added Panasonic FC cabs (but only 47uF in addition to the Tantal).
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I think what you're trying with the inductors on the power rails (+/- 5- 15) of the VIM is a good approach to trying to lower the rail noise. By not knowing the value of the inductors, it's always best to use a scope to make sure you're not creating more noise with the wrong value inductor. If an inductor is not at a reasonable inductance, it can be a problem and make things worse.
On those same rails, I use a 33uf on the +/- 5 rail, because I'm really filtering the worst part of the noise with the inductor. If not using a Tant or electrolytic and there, you would have to use a bunch of various value caps, and that can be very complicated.
So an inductor keeps things simple, but you'll have to go with the right value or something that works without creating more noise and at the same time lowers the noise on the rails.
It has been thought that putting a larger value cap works best there, but that's not the case with video circuits.
| Quote: | As i can see in the service Manual, each opamp has got a Lowpassfilter with 4,7Ohm and 100nF.
Do you think it is a good idea to change all of the 4,7Ohm resistor with a SMD inductor with 3R and 0,68uH (140ma)
On the op amps |
On the Op Amps, I've found that it's best to leave that 4.7 resistor in place. In my mods I do use a series inductor on one of the chips, but not the ones that have the 4.7 resistors. When putting inductors in series on the B+/- supply of a chip, If not the exact value, it can make things worse. And it won't be better than the 4.7 because it's not sensitive to frequencies, whereas the inductor is very frequency dependant.
So I would stay with the 4.7 and from there the focus should be on the caps. The real trick on these circuits are the smaller value caps, not the tant or electrolytic. You'll need tant or electrolytic, but the value is nothing to be picky about. The goal is to find the right value smaller capacitors. And you may have to go with various caps at various values at each chips supply. Depending on the chip being used there, I've had to use up to 4 smaller value caps that ranged in cap value from .001 up to 0.1uf.
You'll also need a tant or electrolytic as well, but the value to use is not that important.
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Revox
Joined: 13 Feb 2008
Posts: 158
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| Posted: Mon Oct 19, 2009 9:33 pm Post subject: |
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Thanks for the long answer. I am studying electrotechnics and i am in basic stuff at the moment (3th semester).
Is there a explanation why noise is getting worse with the wrong inductor?
Does the "power consumer" (the chips) work with the inductor like a resonant oscillator (when the consumer acts like a capacitance?)
I think with an 20Mhz Oskar there is no chance to varify my tuning?
All inductors a in series with the 4,7Ohm R's so i didn't change the RC Lowpass behavior.
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Nashou66
Joined: 12 Jan 2007
Posts: 16171
Location: West Seneca NY
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| Posted: Mon Oct 19, 2009 9:39 pm Post subject: |
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| Revox wrote: | Thanks for the long answer. I am studying electrotechnics and i am in basic stuff at the moment (3th semester).
Is there a explanation why noise is getting worse with the wrong inductor?
Does the "power consumer" (the chips) work with the inductor like a resonant oscillator (when the consumer acts like a capacitance?)
I think with an 20Mhz Oskar there is no chance to varify my tuning?
All inductors a in series with the 4,7Ohm R's so i didn't change the RC Lowpass behavior. |
I added a 56uh inductor that had a DCR of about 4.2 ohms to keep the same resistance factor in tact.
I did not see any issues so far with this. I just made sure the power after i added the inductor was the same value
as with the 4.7 ohm resistor.
Mike why do you add indictors on the PS2 DNP points near the AD835? This looks like the green contrast control goes though here, what is your reason?
Athanasios
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Marquee Modifications and Performance Enhancement
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Mon Oct 19, 2009 10:29 pm Post subject: |
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| Nashou66 wrote: | | Revox wrote: | Thanks for the long answer. I am studying electrotechnics and i am in basic stuff at the moment (3th semester).
Is there a explanation why noise is getting worse with the wrong inductor?
Does the "power consumer" (the chips) work with the inductor like a resonant oscillator (when the consumer acts like a capacitance?)
I think with an 20Mhz Oskar there is no chance to varify my tuning?
All inductors a in series with the 4,7Ohm R's so i didn't change the RC Lowpass behavior. |
I added a 56uh inductor that had a DCR of about 4.2 ohms to keep the same resistance factor in tact.
I did not see any issues so far with this. I just made sure the power after i added the inductor was the same value
as with the 4.7 ohm resistor. |
Maybe Scott or one of the other engineers on the forum can better answer this. I'm not an engineer and why an inductor is not good to use in that circuit is over my head. It's one of those questions I've asked Scott some time ago and have forgot the answer. But do know from trying it, that it's not a good idea. And that would also explain why it's rarely seen in a circuit.. especially one where you're trying to get the best bandwidth performance out of a chip.
| Quote: | Mike why do you add indictors on the PS2 DNP points near the AD835? This looks like the green contrast control goes though here, what is your reason?
Athanasios |
Hmm, where did you get that?? I don't recall showing that aprt of the circuit in the pictures that I posted on this thread.
Just kidding. The reason for why that inductor is on PS2 has to do with U21 being removed from the circuit. If you remove U21, you'll have to jump PS2.
I remove U21 to further reduce noise and the possibility of noise from getting into the AD835. The inductor is a part of a cap/inductor decoupling circuit that i use on the Mikrons to separate or isolate the noise from the CLM's contrast control line to the AD835.
The cap is on the other side of the board.
The AD835 (which is also in the G90, 909, Cine9 and some NEC's) is a noisy chip. Not sure why they did not go with the AD834, which is in the 03 VIM......oh, now looking back, I'm sure it has to do with cost. The AD834 is a 500mhz clean performer. While the AD835 has a bandwidth rating of 250mhz, with a terrible flat response. Which is not good for 1080p bandwidth performance. So that made things a real challenge for me to get that chip where I need it.
I stayed in the whole weekend, and spent a ton of time working on one of my test VIM's and got to finish a project that I had started on sometime ago. This weekend was a wreck concerning my heath, but a great success as far as completing my latest project...
For the past two years I've been working on 02 VIM's, since they are the most common VIM's. I've been using an 02 VIM in my Marquee's over that time period.
The last two weeks, I made great strides with cleaning up the pins on the CRT's with obvious results. This past weekend, I've had greater success in producing cleaner and tighter lines. This made for a more detailed and sharper image. And I'm making this happen using an 02 VIM. I'll be making the same changes to an 03 VIM later sometime this month.
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mp20748
Joined: 12 Sep 2006
Posts: 5689
Location: Maryland
TV/Projector: 9500LC Ultra / Super 02 and 03 VIM
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| Posted: Mon Oct 19, 2009 11:14 pm Post subject: |
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Here's a few shots with the latest changes. I've only decreased saturation a bit, but nothing else done to them.
It's not so easy to see the changes in the shots, but it's very obvious on the screen. No adjustments made to the projector other than convergence after re-installing the boards.
1080P > FullHD > Marquee 9500LC
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