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Discussion Starter · #1 ·
Hi to everybody,


this is my first post on this forum an I start with a more or less big problem/question.


My PJ is a NEC 9PG 2500 hrs form 1994 in fairly good overall conditions.

I just bought it two weeks ago.


But i discovered a leaking cap which has spilled onto the board where it's mounted. (see pic) Its' a 33mF 200V 105 degree-Celsius Elko and it sits about 1/2 inch close to a second one of the same type. Both a located close to some power transistors (you can see them in the lower part of the pic)


1. Can this be a regular part/component failure or is it due to an overload or bad settings of the PJ? Can this type of failure be avoided with better settings?



2. Does it make sense to replace the cap with a 350V one


The strange thing is, that the PJ runs nicely. When I bought it, the seller and I ha it running for about 3 hours without problems. No noise or smell.


I'd appreciate any suggestion or advice.


Thanks in advance


Marco, Germany
 

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Hello DIYcoil


It appear the caps electrolyte has seeped out on top, probably a

defective cap. Since it seems to be in the Switch Mode power supply

It is safer replace it with a cap of the same values unless you know

it is used as a bypass cap (It is likely a bypass since the PJ still works).

Then you can go up to the next value in both uF and voltage. Stay

with the 105C temperature rating.


You might consider replacing all of the can type electrolytic capacitors

since they are 8 years old. I did this on a '94 Marquee 8000. Cost was

$131.45 for over 140 caps and several hours bench time. Everything was improved, but the geometry and convergence controls were improved

the most. It also eliminated a problem with the picture blanking out

and then returning from a very large way out of focus image to normal

size and in focus. (that sequence would take about 2 seconds. It would

happen at least once per DVD movie).


DH
 

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That looks like a cap on the deflection board, and it does not look like it leaked, but something had once spilled on it. Ususally If the cap leaks like that, the top will be split open. I'd say, remove it, clean everything around it, and replace the cap with another one like it.


Marc
 

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I have to agree with Tinman - it doesn't look like the cap has leaked.

If it had been stressed, usually the black plastic shrinkwrap will have shrunk or look stressed from the heat (and/or) the cap would be bulging in the middle (and/or) the top would be cracked open along the dents that are there specifically for that purpose.


Which way is up normally? Is the top of the cap up? I ask because it looks like something dripped onto the top and then ran down the side.


Kal
 

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If you look closely, you can also see a bit on the wire above the cap.


Marc
 

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Discussion Starter · #6 ·
Hello DH,

Hello Tinman,

Hello Kal,


usually the top of cap is facing down as the PJ is mounted at the ceiling.

But you might be right as when the PJ is not mounted, like for transport, the top of the cap would be facing up and some fluid could have dropped onto it through the grid of the hoodlike cover of the 9PG.

I was just wondering about the area at the bottom of the cap where it is attached to its board. It seems to be corroded. I will make an acidity test like with lakmus paper to see if the remains on top of the cap are acidic. (elektrolytic fluid shuold be acidic isn't it?)


@DH The replacement of all the caps is a good advice as they are almost 10 years old.


Thank you very much to all of you guys. I do indeed heartly appreciate your advices as here in Germany only few people seem to know about 9PGs.


I soon will attach an image of the board-area in order to give you a chance to identify its function.


Marco
 

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The board?

it's the deflection board on top, the cap is in the corner next to the deflection yoke connectors and the big black heatsink. :)


Marc
 

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Marco,


If you have an ESR (equivalent series resistance) meter, you should measure the cap in-circuit. If it really has blown, it'll measure extremely high as the fluid has drained out to some degree and the cap will have dried up inside, causing the equiv. series resistance to skyrocket.


You could also desolder the cap to take a look at the bottom of it for any signs of strain.


Do you have a service manual? (What's this cap used for?) If it's in parallel with the other one there, they're probably caps for holding a supply rail charge. One may prove to be enough, though is most likely better.


Kal
 

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Discussion Starter · #9 ·
@Tinman


You ARE a NEC Fanatic!! Your description of the board is exactly as it looks like. ;-)

You might probably have an answer to a general question I have about the 9PGs. I have been told that the 9PG tends to fry its hybrid transistors like nothing when the setup is not performed the right way. Is this true and if yes, what are the right settings in order to avoid this problem?


The remains on the cable are there because i moved them around to get a better view for the picture. But you are right as they did not cover the cap when i first noticed the spill.


@Kal


I do have regular meter and a LCR bridge meter (for caps and coils as my hobby is DIY Speaker building) I am don't know if those meters are able to perform the ESR measurement. I should probably desolder the cap and check it that way. Do I need a special welder/solder on which you can regulate the watt and voltage of the welding tip? Or will a standard welder/solder do? Passive crossover welding is not a real skillful job, you know.


I got a service manual with the PJ but the circuit prints are missing. I could not find a complete service manual doc or pdf in the web. Do you know any download location for it?


You're so fast in replying that I can barely keep up answering myself. What a great forum....!!!


Thank you again


Marco


P.S. I'm german, so it takes me some time to write in english.
 

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The PG's fry the STK392-40 Chips. These are the amplifiers used for convergence and focus on the C-drive and F-drive boards between the CRT's. The key here is to zero out all the adjustments, and mechanically aim and set up the projector so you don't need excessive electronic correction. The more correction you use, the hotter these 3 chips run, untill they fail. If you are working on the unit anyway, just change them out for new ones now. They are cheap and easy to get. So if you do your setup right, a new set of chips should last you many years.


Marc
 

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Originally posted by DIYcoil
I do have regular meter and a LCR bridge meter (for caps and coils as my hobby is DIY Speaker building) I am don't know if those meters are able to perform the ESR measurement.


I don't think so - an ESR meter measures low resistance while passing high frequency signals through the device. You can build them in kit form for about $50.

I should probably desolder the cap and check it that way. Do I need a special welder/solder on which you can regulate the watt and voltage of the welding tip? Or will a standard welder/solder do? Passive crossover welding is not a real skillful job, you know.


A standard soldering pencil in the 20-40W range should be fine. I wouldn't use a high wattage gun though.


Kal
 

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Kal,


And what's wrong with a high school 10lb. American Beauty soldering Iron?


It's all about skill and finesse while using a slegehammer to repair a watch.


Marc
 

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Discussion Starter · #13 ·
@Marc


It might be that those STK392-40 Chips have alraedy been replaced as almost all the chips and the heat or insulation pads under the chips on that long black heat sink look brand new. (I will have to check that when I come home tonight and post a picture tomorrow. I have no internet yet at home as I just moved. So I'm posting from the office.)

With "machanically aim" you mean using the right Scheimpflug-Spacers and fine tuning the convergeance by hand adjusting the lens guides with the screws in the long-wholes on the metal bridge on top of the space between the CRT and the lenses? This goes only for the red and blue lenses, as the green lens has no adjustment possibilities besides the spacer, right? (Sorry for asking maybe stupid questions. It's the first time im setting up a CRT-PJ.)


@Kal


I have to check the manual of my LCR bridge as I remember that ist uses high frequency to measure cap and coil values.


My soldering pencil is a 40w one, so that one will do.


Marco
 

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Mechanically adjusting includes centering the raster and static convergence using the centering magnets on each CRT with static set to 0.


The pads under the heatsinks always look new. Hey, if it's stable, you will be ok. If the Projector drifts a lot, you may need those STK's.


Check your PM.


Marc
 

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DIYcoil,

The main reason for the STK failure is STATIC adjustment,you should avoid any static correction as it passes DC through the deflection coils.

Like Marc said,Zero out the setup and then do the mechanical adjustments,make sure the cross-hair is dead center first,without any electronic correction .
 

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Quote:
Originally posted by Tinman
And what's wrong with a high school 10lb. American Beauty soldering Iron?

It's all about skill and finesse while using a slegehammer to repair a watch.
Nothing! As long as you don't expect the thing to work after! :D


Kal
 

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Discussion Starter · #17 ·
BenY,

Quote:
The main reason for the STK failure is STATIC adjustment
I thought my 9PG has EMF focus, or am I mixing things up here? :eek:


Marco


P.S. As I said, I'm a freshman.
 

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He means the STATIC convergence adjustment - that is, the one you get when you press the STATIC button on the remote control.


- David Eddy
 

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Although I have replaced the STK on the F-board due to really bad base setup once. The overcorrection was so severe that one day there was no edge focus at all. It burned one of the leads on the STK clean off when it let go.


Marc
 

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Discussion Starter · #20 ·
dje,


now i got it. It's kind o' hard to get through the manual without being able to have the PJ running. I keep him grounded as long as I haven't changed the Cs. I have very little experience with setting up the 9PG yet, so thanks for being patient.


I checked the hood of the PJ and it's absolutely clean. No residues of a possible spill at all. Also the inner metal mesh of the hood is clean and there it would have been possible to see residues of that yellow stuff if it would have entered the housing.


I also checked the C more closely and I figured out that the metal cap (with the K-shaped marks) on top of the C is dented inward. As soon as I will have replaced and checked the C I will confirm the possible damage here in the forum so that everybody can tell that a similar appearance is a sign for a damage or not.


One more general question:


What is your advice for cleaning the board. Which fluid is best for a thorough cleaning without damaging the board itself?


If would be better if you could tell me the name of the substance and not a brand as it will be very hard to find the same products with the same brand names here in Germany.


Thank you again to all you folks for your advices and help


Marco
 
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