Prob. with overall focus on Nec 9PG

[Archos27]

I´ve had a Nec 9 PG for a couple of weeks now. The convergence is just fine, but I have trouble with getting even focus all over the screen.

It is possible to adjust center and edge focus separately so that I have either focus in the middle or on the edges. But I can´t seem to get a good adjustment all over the screen. It gets a bit dim. I know I may have to compromise for allover focus, but this is not "acceptable". Will astigmatism (shape of dots) have anything to do with it? Any other idea what might be wrong?

 

[rob12770]

hi, i had the same issue with the barco data 650, it is my first crt pj and for a while i was unhappy with the overall focus, i then discovered that throw distance was very imprtant compared to lcd machines, after a couple of changes i am now very happy with the focus, you do not mention electical focus, im not sure if the nec has this as the barco does, if you dont have a manual there is a pdf document one here for your pj,

http://beamer.xs4all.nl/Manuals/Installation manuals/Nec 9PG/6pg.pdf

sorry i cannot be of more help as i dont own an nec, but im pretty confident that you WILL get the focus you want, its just a matter of tweaking the right knobs or moving the projector i beleive,
im kind of new to all this crt stuff and learning like you

 

[helipilot]

The nec is a bit of a complex beast but will reward you with a superb image once everything is bang on.

There are many things that can affect the focus on a nec.



Optical focus :- (safe for newcomer to adjust)

on each lens there are two wing nuts the one nearest the front will allow you to adjust corner focus. The one towards the back of the lens will allow you to adjust centre focus.



Asigmatism :- (experienced crt person only)

This can have a major effect on the relative focus between the edge and centre if badly set up. This is adjusted by moving magnetic rings at the rear of the tube. This adjustment involves adjusting the shape of the electron beam as well as its size. Adjustment of this is not to be recommended for the newcomer to CRT as 35,000 volts is buzzing about very close to where you have to work.





focus pots on Deflection board :- (experienced crt person)

These control the mid point centre focus adjustment.



moving focus coils on tube :- (experienced crt person)

This can also adjust the mid point centre focus adjustment.



Centre focus control from remote:- (safe for newcomer to adjust)

use this obtain sharp focus at the centre of the screen.


Edge Focus control from remote:- (safe for newcomer to adjust)

Put up cross test pattern (the one that comes up for static convergence.) Use Horizontal edge focus to sharpen the start and end few inches of the horizontal line. As you adjust this control you should see the line get thicker and thinner at its ends.
Use vertical edge focus to similarly adjust the start and end of the vertical line.





If adjusting the focus using the wing nuts and remote control do not cure your problem you should seriously consider getting the help of an expert like Gordon or Roland to help you.

A point worth noting :-

on the nec you have separate centre focus control for each of the three tubes however edge focus affects all three tubes simultaneously. This means that you must get the centre focus for each tube correctly set before attempting to adjust edge focus.

You should check that the edge focus control actually does work by switching off two tubes at a time so that only the red tube is running (now check horizontal and vertical edge focus does have an effect) then only the green tube is running (now check horizontal and vertical edge focus does have an effect) then only the blue tube is running. (now check horizontal and vertical edge focus does have an effect). Note that edge focus is very subtle and you will need good optical focus to see its effect clearly on screen.

The vertical edge focus is controlled by a single chip inside the projector.
The horizontal edge focus is controlled by a different single chip inside the projector.

It is virtually unknown for the vertical edge focus chip to fail however the horizontal edge focus chip can be a little weak and it is not unknown for it to fail.

Try the wingnuts and the focus controls from the remote and let us know how you get on. If nobody has been fiddling inside the machine you should see some improvement or at least have a better idea of where the problem lies.

 

[Archos27]

Thanks Helipilot!!

Unfortunately the projector isn´t where I am at the moment. I think the problem is about astigmatism and beamcentering! Do you or anyone else have a photo that shows where "focus pot on deflection board" is located?

"focus coil on tube" - is that the same the ring that adjusts position of the beam?

 

[helipilot]

Do you or anyone else have a photo that shows where "focus pot on deflection board" is located?

Nope ! If you have the projector sitting on a table and you open the lid. imagine you are standing at the back of the projector looking over the now open lid. You will see a large circuit board which covers the tubes. In the bottom right hand corner you will see a switch marked DEFOCUS. just beside it you will see three pots these adjust blue focus, green focus and red focus.

"focus coil on tube" - is that the same the ring that adjusts position of the beam?

No ! the focus yolk contains the focus coil which has I think, five wires coming out of it. working from the front of the tube backwards you have :-

main deflection yolk (black plastic casing) which handles convergence controls and raster centering (grey plastic rings with tabs)

focus yolk which handles centre, horizontal edge and vertical edge focus. (black plastic casing)

CPC 4 pole magnet which controls the shape of the beam (grey plastic rings with tabs)

CPC 2 pole magnet which controls the centering of the beam (grey plastic rings with tabs)

 

[Archos27]

Thanks again!

Just one or two more questions..

I have had a Ampro 4000G before so I´m not a total beginner. I think I caused this mess myself trying to adjust astigmatism. I did it sucessfully on my Ampro but I guess I didn´t know quite what I was doing when trying on the Nec .

I now found the pots on the deflection board. To bad I didn´t have your answer written on a paper when I was by the Nec. I´m still not sure what you mean by the focus coils on the tube, but there should be one on each tube so I´ll probably find it!

There is a white plastic small "board" over the blue tube with three twistable knobs on it. On top of the board it says "focus", under the text there are three buttonlike things and under them are the twistable knobs where it says "screen". Are these for adjusting gain for the tubes? It looks like it when you twist them.

Let´s say everthing is a mess an I want to start all over with rastercentering, astigmatism and so on (I´m aware of the risks and I only use one hand in the projector covered with a thin rubberglove). Besides, you never get experinsed if you never begin..

In what order do I check: astigmatism, beamcentering, optical focus, focus coil on tube, focus pots on deflection board and remote focus? I understand that you have to go back and forth, but there should be some kind of order of how to do this properly and how to exclude/adjust one thing at a time?

Thanks!

 

[helipilot]

There is a white plastic small "board" over the blue tube with three twistable knobs on it. On top of the board it says "focus", under the text there are three buttonlike things and under them are the twistable knobs where it says "screen". Are these for adjusting gain for the tubes? It looks like it when you twist them.

These control the G2 voltage and will have a major effect on tube life and greyscale tracking if not properly adjusted.

If you have only adjusted the cpc magnets then start there and get them dialed in a bit better before looking to adjust other things.

Before going any further I would have a good read at this thread over on AVSforum :-

http://www.avsforum.com/avs-vb/showthread.php?s=&threadid=98042


You have an Electromagnetically Focused Projector so pay close attention to astigmation adjustment in that section of Guy Kuo's post. The Nec 9 does not have dynamic astigmation controls.


This is not purely about the NEC but will give a great starting point.

I´m still not sure what you mean by the focus coils on the tube

I will post a picture that should help you.

 

[helipilot]

Here is a photo showing the various parts that are fitted to a NEC 9PG tube :-

 

[Archos27]

Perfect!

I bet many Nec owners with focus problems will be helped by this thread!

 

[BrianCurran]

Alan

Thanks also, for the GREAT post.

Don't suppose you fancy a field trip to help setup my 601e?

Regards

 

[helipilot]

Don't suppose you fancy a field trip to help setup my 601e?

Brian,

It looks like you are a bit far away for a quick look.

A NEC setup from scratch is probably around 6 to 8 hours work and that only covers one input, resolution and refresh rate. Additional entries would probably add about an hour each.

Its then worth leaving everything to "settle in" for a few weeks and then probably about hour to very fine tune.

Then ...... If you want the absolute best from your projector its worth getting the greyscale ISF calibrated.

Like most folks on the forum this is just a hobby for me, however Gordon at Convergent-AV might give you a quote.

 

[BrianCurran]

Alan

I spoke to Gordon last year, his quote was significantly more than I paid for the projector. Enough said.

Obviously, I would cover your expenses.
What is your local airport?

Regards

 

[Archos27]

Thought this might help others too so I hope it is ok with you Alan that I post your pm answer.

I can´t see much change at all when trying to adjust both horizontal and vertical edge focus! Where are these chips located? Are they welded? Expensive and hard to find? Can I find them in any store that sell electrical equipment, or do I have to order from Nec?



"Assuming the projector is ceiling mounted:-

open the case

now loosen the deflection board (2 screws towards rear of projector) and swing it down. If you look up between the red tube and the green tube you will see two circuit boards very close together. The one nearest the red tube is the focus board and the one nearest the green tube is the convergence board. these boards are screwed to the projector floor which acts as a heatsink for them. If you look carefully you will see the focus chips flat against the projector floor.

The focus chips are soldered in. The STK 392-040 controls horizontal edge focus and the STK 4275MB controls centre focus and vertical edge focus.

NEC no longer have any stock of these chips. You can pay between £12 and £60 for these in the uk and if you order from America around £15. I have tried various STK 392-040 chips and have found that they vary in quality. If you ever have to replace an STK chip you should add a heatsink to help dissipate the heat. I have been succesfully running a cheap chip with an additional heatsink for around 8 months. Without the heatsink the cheap chips blow after about 3 weeks !

You might want to check out a post I made over on avsforums.


http://www.avsforum.com/avs-vb/show...light=first+aid


Horizontal Edge focus is very subtle and you will only see it working if everything else is well setup. Vertical Edge focus is even more subtle. You will only see it work if you look in the right area of the screen. If your optical focus is not tight it will be difficult to see the effect at all."

Here is another good document for the PG mechanical setup:
http://hem.wtnord.net/k00502/nec9pgsetup.pdf