| View previous topic :: View next topic |
| Author |
Message |
gjaky
Joined: 05 Jun 2010
Posts: 2790
Location: Budapest, Hungary
|
 Link Posted: Sat Jul 25, 2015 5:26 pm Post subject: |
 |
|
| koldby wrote: | As the output stage in new and old VNB is very similar (except for the transistors used, one could probably translate the -1,4 to " Q12 to the same in the new VNB.
I donīt think it is just a matter of adjusting G2/Drive. Aparently the outputstage has some issues in linearity and dynamic range. |
I did not meant that all you have to do is re set these values, I just noted that you most probably must re set these, there might be other problems of course. I have a working test rig for the old VNB, but I don't even have a new style VNB, so all I can do is analyse its schematic diagram here. 
| koldby wrote: |
Why did they change the inputstage to HFA1100 and an emmitterfolower? Is the Z-in of 2SC4271 much lower than MRF5943? |
I'm not sure about the emitter follower, but I seem to remember at that point the CLC449 became obsolete too.
| koldby wrote: |
Why did they change the I-sense/Over-I stage? |
If you look it closely you'll see the I-sense circuit isn't changed, the Over-I has changed, but only just a little. As you could see from my first post in this thread, if Over-I trips it disables the HVPS, causing a no picture situation, I assume that isn't happening with these new boards during normal conditions, so that little change isn't affecting your picture performance.
| koldby wrote: |
Why did they change the Brightnes driver and spotkill? |
This is a good question. Scott told that the clamping circuit was removed from the new VNB, because it wasn't needed since the signal was already DC clamped on the VIM. This is true, however I think the clamping circuit on the neckboard is useful because it can cancel the drift of the output stages, which -therefore- might affect gray scale and long-term performance stabilty.
And since the brightness controll and the spotkill circuit was a part of the clamping loop they had to be redesigned eventually.
| koldby wrote: |
VDC had supposedly only simulator customers as their goal, and that calls for LUG tubes. Did they make the changes to be better with very hard driven LUG tubes , beside the fackt that they couldnīt get more Motorola transistors? |
What do you mean by the term the LUG tubes harder to drive?
_________________
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
|
|
| Back to top |
|
 |
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sat Jul 25, 2015 8:06 pm Post subject: |
|
|
Not LUG harder to drive but simulator pj are driven harder than HT pj are.
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sat Jul 25, 2015 8:07 pm Post subject: |
|
|
And maybe the smaller spot size calls som different settings or preferences in the drive board?
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sun Jul 26, 2015 8:49 am Post subject: |
|
|
| gjaky wrote: |
This is a good question. Scott told that the clamping circuit was removed from the new VNB, because it wasn't needed since the signal was already DC clamped on the VIM. This is true, however I think the clamping circuit on the neckboard is useful because it can cancel the drift of the output stages, which -therefore- might affect gray scale and long-term performance stabilty.
And since the brightness controll and the spotkill circuit was a part of the clamping loop they had to be redesigned eventually.
|
So you think maybe the missing clamping could be the reason why some say that the grayscale @ contrast >50 suffers?
Do you think you could come up with some good modification suggestions if you had one of the new VNB?
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
gjaky
Joined: 05 Jun 2010
Posts: 2790
Location: Budapest, Hungary
|
| Link Posted: Sun Jul 26, 2015 9:16 am Post subject: |
|
|
| koldby wrote: | | gjaky wrote: |
This is a good question. Scott told that the clamping circuit was removed from the new VNB, because it wasn't needed since the signal was already DC clamped on the VIM. This is true, however I think the clamping circuit on the neckboard is useful because it can cancel the drift of the output stages, which -therefore- might affect gray scale and long-term performance stabilty.
And since the brightness controll and the spotkill circuit was a part of the clamping loop they had to be redesigned eventually.
|
So you think maybe the missing clamping could be the reason why some say that the grayscale @ contrast >50 suffers?
Do you think you could come up with some good modification suggestions if you had one of the new VNB? |
Actually what the problem look like? Can it be caught on a photo?
Maybe I could work out a solution, but first one should ask Scott (tse) about the problem, because I heard he was aware of this too, and if anyone he will know what the problem really is.
_________________
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
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sun Jul 26, 2015 10:48 am Post subject: |
|
|
Aparently when you turn up the contrast >50 the grayscale cannot be maintained correct when you go from 10% IRE to 100% IRE.
And the blaclevel is unstable, flashing like unstable DC level..
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
gjaky
Joined: 05 Jun 2010
Posts: 2790
Location: Budapest, Hungary
|
| Link Posted: Sun Jul 26, 2015 11:36 am Post subject: |
|
|
| koldby wrote: | Aparently when you turn up the contrast >50 the grayscale cannot be maintained correct when you go from 10% IRE to 100% IRE.
And the blaclevel is unstable, flashing like unstable DC level.. |
Below 50 contrast everything is OK otherwise?
_________________
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
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sun Jul 26, 2015 12:40 pm Post subject: |
|
|
| gjaky wrote: | | koldby wrote: | Aparently when you turn up the contrast >50 the grayscale cannot be maintained correct when you go from 10% IRE to 100% IRE.
And the blaclevel is unstable, flashing like unstable DC level.. |
Below 50 contrast everything is OK otherwise? |
You got PM
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sun Jul 26, 2015 12:43 pm Post subject: |
|
|
| gjaky wrote: | | koldby wrote: | Aparently when you turn up the contrast >50 the grayscale cannot be maintained correct when you go from 10% IRE to 100% IRE.
And the blaclevel is unstable, flashing like unstable DC level.. |
Below 50 contrast everything is OK otherwise? |
A comment from someone who knows the problems better than I do:
"It behaves the best with contrast below 50, but its not clean, it has a lot of distortion and noise issues.
Remember my reference point is very different than any standard Marquee video chain, so you might think its ok compared to a standard old style neck board."
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
koldby
Joined: 07 Feb 2007
Posts: 126
Location: Denmark
TV/Projector: GJAKY modded VDC marquee 9500lc ultra
|
| Link Posted: Sun Jul 26, 2015 12:55 pm Post subject: |
|
|
| gjaky wrote: |
I'm not sure about the emitter follower, but I seem to remember at that point the CLC449 became obsolete too.
|
Regarding this, I dont think that is the reason. They still use the CLC449 in the VIM02 boards.
_________________
What is home theater without good sound?
|
|
| Back to top |
|
|
|
|
Forum FAQ
Search
Memberlist
Photo Albums
Register
Profile
Private Messages
Log in
