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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sat Feb 20, 2016 7:26 pm Post subject: |
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Hm, increasing the inductance a little may help. In the 1209 neckboard there is a 330nH inductor, this gives fres of 87,6 Mhz. Also reducing the resistor may increase peaking.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 7:39 pm Post subject: |
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Ok now I understand the second external peaking. If this one does not help....
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 7:51 pm Post subject: |
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That L2 coild is soldered undernead takes hot air to replace I think.
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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: Sat Feb 20, 2016 8:03 pm Post subject: |
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| the dude wrote: | | Quote: | | Mike removes those diodes from the Marquee neckboards |
Mike removes everything he does not understand  |
They are Motorola Rf Transistors and do not need the ARC Diodes. And that is why the transistors HAVE not been failing. That is not the case on the newer VDC boards, those transistors need those diodes. And one further, let me once more remind you that my work has also been under careful eyes as to what I have been doing. There's a lot you don't know, but that means nothing to you at all, but hopefully one of the others here that really understand what's doing on technically can teach you a thing or two about needlessly insulting others.
And when the day comes when you have made a change that's worth talking about or something you can be known for making happen, it's only then that I'll see you as being someone beyond taking a flashlight battery and making a bulb lite up
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sat Feb 20, 2016 8:16 pm Post subject: |
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| Quote: | | They are Motorola Rf Transistors and do not need the ARC Diodes |
Sure. Until a arc ocours. And those engineers that have designed it that way are also just behind lighting a flashlight bulb.
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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: Sat Feb 20, 2016 8:26 pm Post subject: |
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| the dude wrote: | | Quote: | | They are Motorola Rf Transistors and do not need the ARC Diodes |
Sure. Until a arc ocours. And those engineers that have designed it that way are also just behind lighting a flashlight bulb. |
The transistors were not designed that way, the original board design had the diodes on the boards. Now why they are not needed is the mystery that I'm not going to reveal.. 
But to assume you know and understand everything is why you can't wrap your mind around why those transistors HAVE NOT failed the past tens years.
I know but I'm not saying.. ...and that is the facts.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 8:42 pm Post subject: |
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Look at this 470nH on L2 it is almost even in reality. No overshoot on lower frequencies.
 Untitled by Radio Head, on Flickr
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sat Feb 20, 2016 8:58 pm Post subject: |
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Thats 470n? Is there a thread for this photo?
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 9:11 pm Post subject: |
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| the dude wrote: | | Thats 470n? Is there a thread for this photo? |
You mean the testpattern? Yes it is 470nH but there is also something weird happening. When I change contrast something like streaking seems to happen. I think it is overshoot do not know. Swapping back to unmodified board the streaking is gone so definitely it is the mod.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 9:20 pm Post subject: |
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I think I need to scope the output with my new 300MHz scope when it arrives  Only the scope and 10pF on it.
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Last edited by redfox001 on Sat Feb 20, 2016 10:06 pm; edited 1 time in total
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sat Feb 20, 2016 9:23 pm Post subject: |
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So, i just unsoldered the 330n from the 1209s neckboard and put it on the 909. Since i have a hotair station soldering was pretty easy.
I think it helped a litte. Reducing the resistor was not helpfull. I is already quite low, remember we have a high drive voltage and so it would not limit current to much.
I will order some inductors for testing next week, and then we will see.
@Mike:
And now for some conciliatory words... I see you are a men of practice and for sure have more experience than me. But you also give some questionably advice here. For sure you can replace a fuse in your house with a straigt wire, and you may experience that nothing bad happes. You can repeat that for the houses of your frieds too, and maybe you will never get in trouble. But that does not prove that there is not a very good reason for the fuses. If you want to improve it, put more diodes in series to reduce capacitance. You need to realize that the guys at barco, electrohome and other companies where smart guys that did a good job in general. Today HD resolution is the only importand one, and so we can tweak the machines a little with this in mind.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 10:02 pm Post subject: |
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Do you have no streaking? In my picture you can see the lines continuing to the right. They should not.
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the dude
Joined: 11 Sep 2013
Posts: 179
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| Posted: Sat Feb 20, 2016 10:07 pm Post subject: |
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On the pictures it looks like there is little streaking (look at the fields under the 1:1 field), but i haven't seen it on the screen, so i think its fine.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 10:22 pm Post subject: |
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Ok I have seen some streaking before at low contrast now it is at high contrast. I put in a bigger inductance so outside the resonance the gain is lower. Perhapsi have to set the resistance lower to compensate. I see tomorrow what the light output now is.
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gjaky
Joined: 05 Jun 2010
Posts: 2802
Location: Budapest, Hungary
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| Posted: Sat Feb 20, 2016 10:36 pm Post subject: |
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| mp20748 wrote: | | the dude wrote: | | Quote: | | They are Motorola Rf Transistors and do not need the ARC Diodes |
Sure. Until a arc ocours. And those engineers that have designed it that way are also just behind lighting a flashlight bulb. |
The transistors were not designed that way, the original board design had the diodes on the boards. Now why they are not needed is the mystery that I'm not going to reveal..
But to assume you know and understand everything is why you can't wrap your mind around why those transistors HAVE NOT failed the past tens years.
I know but I'm not saying.....and that is the facts. |
It'really not a mystery it's all in the datasheet: those transistors are "emitter ballasted" ones. Power RF transistors are usualy made of multiple lower power transistor tied in parallel on the same die, with emitter ballasting the emitters are tied to the terminal through a small resistor, that is very common with parallel transistors. This, however only helps to distribute the power between the transistors inside the die, especially with impedance mismatched networks. A spark still can destroy the transistor if it exceeds the maximal breakdown voltage of the transistor, and not meet the spark gap's ignition voltage, the diode sure helps then steering the currents to the supply or ground.
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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, VIM-DB
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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: Sat Feb 20, 2016 11:05 pm Post subject: |
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| gjaky wrote: | | It'really not a mystery it's all in the datasheet: those transistors are "emitter ballasted" ones. Power RF transistors are usualy made of multiple lower power transistor tied in parallel on the same die, with emitter ballasting the emitters are tied to the terminal through a small resistor, that is very common with parallel transistors. This, however only helps to distribute the power between the transistors inside the die, especially with impedance mismatched networks. A spark still can destroy the transistor if it exceeds the maximal breakdown voltage of the transistor, and not meet the spark gap's ignition voltage, the diode sure helps then steering the currents to the supply or ground. |
Yes it is, but you still missed it....oh, and I also remove the exact same diode from the Input of the first stage on the neck boards, and never had one fail..
Now when I mentioned this to certain engineers and what/why I was doing it, they were amazed. And they also agreed with me that I shouldn't need to worry about arc failure, and as time went by, they along with myself were right about this..
And that's only one of the many tihngs that I've been able to prove the theory wrong on. But why is it, that these devices did not need that diode....I'm not asking a question here, because it's still a mystery..
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sat Feb 20, 2016 11:30 pm Post subject: |
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I think that if you are making thousands of those Marquess you want to exclude any risk. If you mod a few you can take some more risk. However two motorolla on one modded neckboard had died when I got it from you. Makes me think.
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sun Feb 21, 2016 12:16 am Post subject: |
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This is the whole story on the neckboards quoted from another forum
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I think it might become a bit confusing as now I handled two problems on two neckboard but the next problem was even more difficult to solve. This third problem was the gain on a high bandwidth neckboard. I agree that normally you would just toss the neckboard into the bin when you are facing a problem that the gain is just to low. But this neckboard had been modified and the bandwidth was very good but the gain was very low. In practise this ment that I could not use the board on green. I had to set the green drive to 100 and the red and blue drive to 0 and even than the greyscale could not be calibrated. There was to little green. Aside from that the light output was something like 5ftL and that is just to low.
So I had to hunt this board for gain issues.
I started by measuring the voltages on the power rails as I reasoned that low power means low gain. However these measured +-85V and +-5V so nothing wrong there. One of the 400 Ohm resistors measured 370 Ohm so to be sure I replaced with another one that measured 390 Ohm but than the gain was even lower.
In the next post I will show how I replaced two of the motorola transistors in the end and how I found out they where wrong. I still have questions trying to understand how this board could function at all with two dead main transistors. Perhaps someone can explain that. I will write what I understand of the schematics.
Read more: http://repairalmostanything.com/thread/179/marquee-9500-neckboard-repairs#ixzz40kzgOAsm
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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: Sun Feb 21, 2016 12:19 am Post subject: |
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| redfox001 wrote: | | I think that if you are making thousands of those Marquess you want to exclude any risk. If you mod a few you can take some more risk. However two motorolla on one modded neckboard had died when I got it from you. Makes me think. |
That was so strange, because that was the ONLY neck boards I've heard with failed Motorola's Hmm...
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redfox001
Joined: 16 Mar 2009
Posts: 2257
Location: The Netherlands
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| Posted: Sun Feb 21, 2016 12:48 am Post subject: |
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In this thread you have been cought several times. Perhaps we are not as stupid as your average type of customer
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