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Discussion Starter · #1 ·
I just spent the weekend working on an XG and a couple of PG projectors with VDC tubes.


I was realy disappointed with the focus on all tubes, especially the corner focus. Despite the fact that the MEC VDC rebuilt tubes are seemingly flawless, these NEC's aren't cutting it.


Is it just me, and did I have a bad day on the service bench, or have others experienced this?


Eric at crtcinema says he has had problems too...


Curt
 

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No Curt, you are not alone. I have done a full setup on a PG Xtra recently, and try as I may, I could not get the focus as good on the 2 VDC tubes as the original. I was disappointed by this as well. The picture still was quite good, but soft. I'll stick to original for my own use for now.


Marc
 

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Curt

Did you get these tubes from Charlie (VDC) or elsewhere??

The old G-70 tubes were like that but the most recent ones I've installed have been quite good.

I haven't tried any XG CRT's from NEC as we have been using NEC tubes when we need them.


Terry
 

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Curt,

Id let Charlie know about this, I wish we could get him to watch the forum more to get a pulse on it, I know when the MECS had problems he corrected it. Im wondering if he changed guns? I hardly doubt he changed the phosphor formula, he used NEC phosphors in the past but that shouldnt affect focus unless the coating thickness might play a roll, did you move the focus coil up and back? Doug
 

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Curt,


We used about 10 of the rebuilts a coupe fo years ago and had issues with every one. Since the NEW NEC CRT's are actaully cheaper, we just keep using them. Good luck getting them from NEC however. Sometimes the lead time is 12 weeks.


I'm sure VDC will continue to improve them, especially once NEC discontinues them completely.
 

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On a scale of 1-10 where would you rate these? Are they useing OEM guns to rebuild these tubes?


Chip S.
 

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Guys!


I had issue with some nine inch Marquee tubes from VDC recently, and the problem was determined to be....... me! I neglected to clear all the hot melt glue from inside the scan yokes, and this prevented the entire yoke array from being forward enough on the neck. So, check your own work before you flip out!!!!! :D
 

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Discussion Starter · #8 ·
Well, I put the XG tube into two sets, and carefully made sure that the original NEC tube had good focus (but was badly burnt). THe VDC tube did not have good corner focus, so I pulled it back out again and will send it to VDC soon.


I can't really rate tubes, they're either a 10 or a 0...:)


I'll be playing with a bunch of PG projectors this weekend, some have new and some have VDC tubes. I'll report back..


I will also be retubing two 9500LC's that I finally got in, so I finally get to play with serious 9" sets...:)


Curt
 

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Tim and others,

I have seen this myself, many times.


Where the old tube was set up at doesnt mean its going to be perfect for the new tube, theres a lot of variables that need to be looked at.


New NEC tubes are easier to do then rebuilds but can be brought into spec with working at it to find optimum, this usually starts at the mechanical then to the wave board pots for best center focus, if you dont catch the focus yoke sleeve that centers the yoke (it will fall out) it will affect the overall focus. The astig (purity magnets) mechanical will affect this also as well as the electronic astig and lens inside and outside adjustments.


I have seen a few of the tubes not come in as Curt has no matter what I do and I always think its me. At that point Ill shut it off and take another look at it in the morning.


One last thing that I notice on any tube, new or rebuilt. If it snaps to clear the impurities inside the tube (normal for the first 20-30 hrs) it will usually change the raster position just a tad so the astig needs to be checked again. Its good to run it out as much as you can to make sure its cleared. Doug
 

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I just replaced all three CRT's in my Runco DTV-991 (NEC XG-851). I ordered all three tubes from Runco, got an NEC Red, VDC Green, and a VDC Blue.


The blue CRT came in a box that looked like it had been sent to another dealer and subsequently returned.


The packaging consisted of the usual foam at the face end of the box, but rather than the cardboard insert that protects the neck of the tube, there were 4 peices of foam surrounding the neck.


The serial # is on the box is 49294.


The ceramic support inside the tube is not the same color as the other two tubes, it is a brownish pink, where the other two are light blue.


The coating inside the neck is brownish, not grey.


There are obvious ripples where the new neck was attached to the older bell and face.


If you are wondering where this is leading to, here is the issue:


The Red and Green CRT's work flawlessly, the NEC has a slightly finer spot size, but both will focus sharply and hold the sharp focus with the contrast run all the way up to 100. Astigmatism adjustment with both was simple and the results are perfect.


Center focus is perfect and edge focus is the best I have ever seen it.


The blue tube, well this &%[email protected]*() thing is giving me fits. Where to start:


1. The tube would not cut off unless I adjusted the black bias to a value outside the normal 2.5 +/- .1 volts.


2. The astigmatism was a bear, it's just barely OK after a major battle with it, but not at the level of the other two CRT's.


3. Focus degrades at high contrast levels, at 100 the blue crosshatch lines are easily 10 times the width of red and green. (I know blue won't focus as well as red and green, but the original blue tube was much better on focus, although somewhat worn).


4. The edge focus is terrible, in fact it can't be focused.


5. Color temperature tracking is off, I have to boost the blue bright bias and drive to much higher levels than the other CRT's adjustment.


My question:


Did I get one of the early VDC rebuilds from the days before they perfected the process?


Vern


P.S. Tube replacement procedure and setup info courtesy of Guy Kuo and Doug Baisey via AVS.
 

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Discussion Starter · #11 ·
I had this on another post, but I thought I'd repost here since this one was bumped.


The last set of PG tubes I got in were R and G from NEC (originals) and the blue from VDC. I could not get any of them to focus properly, spent a couple of hours fighting with all three tubes.


So I had another PG chassis with working but burnt tubes, so I swapped all three over one at a time and checked the focus after every tube change.


Whaddya know, all three tubes that looked like crap in one set worked perfectly in another.


Problem is now, I'm not sure where the focus issue is on the first set.


Moral of the story is to fully test each set _BEFORE_ retubing, so you don't waste a lot of time chasing a problem that might not have anything to so with the repair that you have just done.


I've had great success with VDC tubes, only one recently had a phosphor blemish that unfortunately I did not catch before sending it out, so that's costing me $300.00 in round trip shipping that I should have caught before selling the set ...:-( VDC will cover the tube though..


Curt
 

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Curt, were the anode voltages on both chassis the same? I wonder if some of the variance was a hidden anode voltage variation between the chassis. I know the HVPS's are supposed to be preset, but maybe it drifted on one of the units.
 

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Hi guys,

The HV is pre set to that unit and the pots are sealed afterwards, the new boards are not pre set and the pots are not sealed to be adjusted to the unit. It does sound like this could be the problem. Doug
 

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Recall that the EM focus coil relies on the electron beam velocity interacting with magnetic field strength. The two together create a series of spiral shaped paths along which the electrons travel. The electrons most central are minimally affected. The ones most off axis are twisted the most back towards the central axis. When the electron velocity and field strength are just right, the paths intersect at the phosphor plane. The CRT normally has its acceleration voltage carefully preset. This determines the bean velocity and is specified to minimize x-ray generation and help control beam energy (to some extent). Now if the chassis' "preset" anode voltage is out of spec enough, the magnetic focus coil has to work a different amount of twist. If the beam is accelerated with a higher potential, the magnetic lens has to work harder and I would expect the electron paths to cross center axis with a bigger spread in distance at which the central and outer paths focus. This conization means the beam won't appear focused even if 2 and 4 pole astigmation are perfect.


So, this leaves us with two possible things to explore as difference between Curt's two chassis which behave differently with the same tubes. Either the available EM coil current range differs or the acceleration potential differ. I guess we could also consider the possibility that some coil loops are shorted, but that's not very high up my list.


Now, I can't quite reconcile why some VDC rebuilds seem to be altering the acceleration potential or EM coil requirements. Possibly the active emission point of the cathode is ending up at a different distace than the factory built units. That would alter the acceleration potential's effect as well as the magnetics. One might be able to compensate by placing the magnetics slightly differently on the tube necks so as to compensate for a different phosphor to cathode tip distance. The EM coil may need to be further back on the neck than normal and the static EM focus adjusted. I'm guessing further back since it's normall quite forward and going further back reduces the EM coil current requirement and might bring an out of spec gun into alignment. As for the CPC assemblies, insufficient range in the 2 pole and 4 pole adjustments may mean the assembly is too far back on the neck to properly interact with a too close cathode tip and grid assembly. I'd try moving the CPC assemblies a few mm forward from normal to see if that helps.


Just some guesses and please be very careful if you decide to check any of these ideas out. Any way you slice it, working at this level on the machines takes a lot of effort, patience, and electrical safety.
 

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I am having a problem with the projector with VDC tubes. Posted here and found the neck board was taken out from a HV arc on the blue tube. The two questions are one, is this common with VDC rebuilds? And second I sent the tube, neck board, and focus coils to Eric Lang for trouble shooting. Is Eric Lang's business proficient on Sony G70's from the very technical level of voltage adjustments as Guy is referring to in the reply above? If so I would prefer to send the entire projector to Eric for a complete going over.
 

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Quote:
Did you order new tubes from Runco and they sent you back Rebuilts?
I ordered replacement tubes. Actually, I ordered them through the Runco dealer where I bought my projector.


No one made any statements about new vs rebuilt, at any time.



Guy: the position of the EM focusing coil makes no difference in the sharpness of focus.



Curt: The original blue is sharp, but worn enough to cause issues with grey scale tracking adjustment when combined with the new red and green.



Matrix: It's common with all new tubes for the first 25 hours or so.



All: So, not yet having an answer to my question, am I to assume that current VDC rebuilds are having the issues I stated in my post above? Or do I, in fact, have an older VDC CRT from the time period when there were known issues?


I find it strange that the ceramic supports in the neck of the CRT are a diiferent color than the new NEC and the good rebuilt VDC green.


I need this info when I talk to Runco on monday.


Searching for the answer.....


Vern
 

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Vern, Thanks for the reply to my question. In your opinion should all the tube related voltages be addressed after a tube change? Thanks, Dennis
 

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Quote:
In your opinion should all the tube related voltages be addressed after a tube change?
Well, not many of us have a HV probe capable of measuring 10's of thousands of volts any more. At one time they were standard equipment for anyone working on TV sets.


Actually, I think you should follow the service manual's instructions for replacing a CRT. This will include the proper adjustment procedures, both mechanical and electrical.


For example, the NEC XG service manual calls out 7 specific procedures to perform after replacing a CRT. HV adjustment is not one of them.


Other than adjusting the focus pots, there is no requirement to touch any other pots on any of the circuit boards in the replacement procedure.


Other manufacturers and models may differ.


I hope this helps.


Vern
 

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Vern, Yes it does help. I feel better about re-installing the tube and board if Eric gives them a clean bill of health after he completes the repair. I just hope the tube does not arc again. Thanks, Dennis
 
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