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Discussion Starter · #1 ·
Hi!


I have bought a used BG800 9 month ago. It had 3800 hours on the counter, now 500 more.


Problem 1:

Some weeks ago the projector started to turn off like granny's old TV set: the picture first disappeared, then a small, but quite bright center point appeared for about half a second (on all three tubes, quite bright visible on the screen, diameter around 1.5 - 2 inches on a 55 inches wide screen).

I have asked for help at a German home theater forum. A technician told me that it is a known problem with the 800 series. There should be a circuit which is responsible for suppressing the spots which are caused by static high voltage when the unit is switched off.

So my first question: Is this diagnose right?


Another guy told me to check the G2 level (visually, with 100% black image, brightenss 50, contrast 0, colour to 6500K )just to be sure. It was too high on the blue, and a little bit too high on red and green after this method. I don't know if this does matter, it's just to tell what happened.

Now the "turn off spot" was much darker, almost unnoticeable on the screen.

But after a few days it seemed to become brighter again.

I was also told that the responsible circuit may consist of just one or more capacitors, at least it is in ordinary TV sets. This sounds evident, a capacitor can die slowly, so the spot getting brighter because the capacitor can absorb the voltage less and less.

A dealer also said there is an additional circuit available for the 800 series to protect the tubes from damage due to high voltage failure. I don't know if my projector is equipped, where would be it's location and how does it look?

Someone said it's a circuit connected to the power supply, but how could that protect the tubes??

Can anyone tell me on which board which elements are responsible for the suppression of the spots (or if it may be caused by something different) so I can check that.

I don't have a service manual, if someone has it scanned, I would very much appreciate if you could email it to me



Now I got another answer after posting this question on the Barco HT forum (not from a Braco official): He said it could be one output amp, a dead transistor. It could also cause spots on all tubes.

I don't undestand how this could be, because the Barco has no problems when it's in use!?


So, does anyone have an idea? I'm really tired of using my small TV...



Problem2:

A few weeks ago while watching a movie, the BG800 made a (quite low) noise like a HV flash over and the picture went off. I don't know if any LEDs were on or off since the cover was closed and I immediatly turned off the unit. After removing the cover and powering up again to see if anything was visible, everything was fine. The projector was working one evening since then, with the cover off, no problems.

When adjusting the G2 level earlier, I noticed a slight prickle when touching the HV wires going from the G2 module to a grey moulded box behind the G2 module which has the 3 wires from the G2 and 3 going to the tubes neck plate.

Could it be that there was a flash over from these wires to the chassis or the ventilation grille which is just beneath the cables?

Would the HV protection engage in this case?

Should there be seen a correlation between the 2 problems or is it just coincidence?


Btw: what is the grey module (box) below the focus module on the right picture? On the left picture is just the one with one input and output (from transformer to module to focus), I have a second with 3 in- and outputs (from focus to tube necks). Is this a protection module? And what is the other one?


I hope you can help me with this, because I really don't want to burn the tubes or cause an (even more?) expensive damage!!!

PLEASE!!!


Dan
 

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Daniel,


When the projector is turned off, everything shuts down including the beam deflection circuitry which paints the raster. Your unit has circuitry in place which blanks the signal so that you don't see the beam collapse on the face of the CRT's as what you're seeing will eventually burn a beam or spot into the phosphor. By the sounds of it, this protection circuitry has now failed. You should have this fixed ASAP to avoid permanently burning in a spot or line in the middle of the CRT's.


Kal
 

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Discussion Starter · #3 ·
Hi Kal,

yes, I have already been told there is such a circuitry and this should cause the prob, and that this will cause burns in the phosphor sooner or later.

I try not to use the pj.

Oh, and I don't see the picture collapse. The picture disappears completely at once like normal (black screen), and then those spots light up for half a second or so. This looks to me like a capacitor who's capacity is to low (partly damaged), so it can't absorb all the energy and the rest of it gives the spots. Does this sound logical? :confused:

Can you, or someone (Curt?), tell me where to look for the bad part, on which board and maybe the parts number (I mean the single capacitor's etc. number on the circuit boards). I have a friend who was a TV tech but hasn't worked as one for many years, but he would certainly find the dead parts if he knew where to search.

After reading a lot in this forum, it seems to me like the BG800 have quite delicate electronics ("30-70 rule"), and my boards have lots of after-manufacturing added parts, mainly resistors soldered parallel to others, looking very botchy:mad: . I also have heard that there is a list of parts which are "endangered". Would be interesting to see it, if it's not a Barco "confidential"... or even more if it is? :D :D

Beeing a student I can't afford a newer pj, or an expensive repair, that's why I hope you can help me.


Thanx

Daniel
 

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Bad solder joints on the transformers on the main power supply board will cause spot burn every time.


Increased G2's will do it as well, but less likely.


Curt
 

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Discussion Starter · #8 ·
Thanks Curt,

I will check that right tonight. That's the most evident cause (in my case), because the spots started, when I had the powersupply removed and reinstalled! I couldn't imagine what should be defective; but it had to be really bad luck if the spots started when I had put my fingers where I shouldn't have;) and it had nothing to do with that...


So like I said, I will check it. Simply resolder all transformer pins? Or can they be broken on the other (not the circuit) side? Should I better remove the transformers to be sure, and then resolder?


Would a too high G2 cause the spots "forever" or would they go if adjusted correctly? I think the G2 is OK now. Black is black:D .


What about the "grey box"? What is that?

And where would be the notorious additional protection module? I have heard about that a lot here in Germany, but I'm not so sure, if it really is a CB on the (main) power supply board. What would such a protection module cost? I've been told it's very recommended to have it to protect the precious tubes!


Another question: There is a 3mm LED on the horizontal deflection board. It's glowing faintly ever since I have the BG800. Is that OK? What is this LED for?


Daniel
 

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Discussion Starter · #9 ·
Hey guys,


the Barco is fine again!

Sorry, Curt, I have removed and resoldered the 2 transformers on the main PS, but the spots were still there. But it was already resoldered, it looked so.

Remember the "grey box" module? The one with 3 hv wires going from the focus board into it and then out to the tube necks? Well, as it is not installed on any other BG800 I have seen (on photos), I have plugged the wires directly into the focus board like it is on the labelled picture.

And, what should i say, ON, waited a Minute, OFF, NO SPOTS!!!!!!:) :D :p

Any explanation? I think, the module had too high resistance, causing the G2 voltage (are the small red wires G2?) to stay on (maybe as static voltage?) too long, instead of collapsing.

Is there anything right in my thoughts? I like to know as much as possible about the function of the things that I use. It's like you can only drive a car optimally if you know hoe the engine, trans etc. work :D (I was a car mechanic before studying...)

So, what is this box good for??? Is it a security part? Should I get a new one?

What about other optional protection modules? Please give an advise.


Thanx to all who helped me, I will certainly have some more questions, and in some cases I even know something usefull :D.


Daniel
 

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Discussion Starter · #10 ·
Hi again,


after watching a complete movie this night (with the kill-switch in my hand :p ) it's still allright!


Please, if anyone knows what the grey box is, tell me!


Curt, as a CRT freak and dealer, you must have seen one of those? If not, I really wonder what it had to do in my Barco!


Daniel
 

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Actually I have never seen this extra grey box.


Anyone else?


Curt
 

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Discussion Starter · #14 ·
I think it was '91. If not, I will tell. But the cover date must not be the date of manufacture... it may be replaced:cool:

When I look at the various boards there are really a lot of modifications made, and lots of transistors (on the RGB end stages (or what are the 3 small CBs above the tubes?), on the powersupply, and on the CB where the focus module is attached) are replaced. At least they look newer than others ;). Hopefully, they are stronger than the originals... Are all PJs so unreliable? TVs almost never have problems (technicians will protest now), but my Barco has definitely seen a lot of service :rolleyes:


I don't have the serial # here, I can tell you that tonight (German night ;) )

But my Barco has a different cover than others I have seen: The small cover has magnetic lock not the pop-up version, and the big cover has 2 quarter-turn screws on top to unlock.


Daniel
 

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Discussion Starter · #17 ·
Hi Kal,


no, I have not searched for the use of it. Maybe Barco would know an answer, I should try.

But as my BG800 works fine (had to replace 1 FET on the red output endstage in the meantime ...), so I don't really care ;-)

I will post, if I find out something about the "greybox"!


Daniel
 

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Quote:
Originally posted by DanielW
Hi Kal,


But as my BG800 works fine (had to replace 1 FET on the red output endstage in the meantime ...), so I don't really care ;-)
Daniel,


The FET you replaced was on the video output (neck) board directly below the RED CRT socket? (see attached photo). I se two FET's in the photo attached to the heat sink at the top. There are a couple of can transistors will radial heat sinks as well... these supposedly die easily sometimes...


What was the problem you were having? The reason I ask is that my blue tube has started to smear to the right over the last few months. Tonight I'll try swapping two of the neck boards to see if the blue one's the culprit. If that's indeed the problem, I'll probably just replace the entire board... but if you have any insights into what transistor (or whatever) may be the problem, I'll just replace the 1 part.


Maybe you had the same problem as me on the red tube?


Attached is the picture of the output board (one for each of the tubes):



Kal
 

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Discussion Starter · #19 ·
Hi,


it was the 2SK511, on your picture it's the left one on the heatsink.

It was quite hard to get in Germany.

The 2 with the radial heatsinks are 2N5583, afaik. They are absolutely not available here, even in the States it's hard. We (a couple of guys from the German forum (that has a bad reputation on the AVS :( )) have placed an order of 100 transistors, thus we could get them for $2 each. Otherwise they cost about $12 each!!! :mad:


The symptoms were:

Red increased like too high G2 setting, I first thought, it's G2 and have readjusted it several times. The background was so bright (over the phosphor area) that I feared for the tubes.

I also had visible retrace lines with a bright vertical bar on one side.

At that moment I decided to repair it.

First I swapped the rgb-output board with the green tube's board. (Not the neckboards, only the output boards). The problem went to green. OK.

Then I simply measured all transistors and diodes with a multimeter (measureing resistance) comparing the defektive and a good board.

I found the 2SK511 to have a quite low resistance between gate and drain (I think), and that's definitively NOT normal for a FET. I rechecked the measure after unsoldering, still too low.


And it was only this small thing causing the problems :D A $1,20 repair.

I would suggest trying the same procedure. It's quick and easy. If you don't find such an obvious malfunction of a transistor (the 2N5583 are normal transistors, so they may not show a defect as clearly), it could be harder to find.


Daniel
 

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Thanks for the feedback Daniel! Some good points you make here... I'm going to pull out both boards and start checking with a multimeter...



The symptoms were:

Red increased like too high G2 setting, I first thought, it's G2 and have readjusted it several times. The background was so bright (over the phosphor area) that I feared for the tubes.

I also had visible retrace lines with a bright vertical bar on one side.

At that moment I decided to repair it.



This is interesting because a secondary problem that I've been having (besides the blue smear to the right) is that my blue tube's G2 has been INCREASING very slowly over the last year. It's an extremely slow increase. I've been going and re-adjusting the blue G2 on the focus block to compensate about once a month, but this can't be good... something's being overdriven, and I'll eventually run out of G2 adjustment!

First I swapped the rgb-output board with the green tube's board. (Not the neckboards, only the output boards).


I'm confused - I thought the neckboards and outputboard are the same thing! The attachment I added above was an output board correct? Is a neckboard the board that has the CRT socket on it? (Not much on that thing so I doubt they rarely 'break'.)

And it was only this small thing causing the problems :D A $1,20 repair.

I would suggest trying the same procedure. It's quick and easy.



True. And with two other boards to compare to, it's pretty easy. I can always desolder a leg of each resistor and check those as well... some of these seem like they're high power resistors and may get hot and be drifting.


My BG800 has over 23000 hours on it so I'm not complaining if I have to pay $1-2 every now and then for new parts! :D


Thanks again!


Kal
 
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