[K7000] Lost sync when screnn is white

[dapsaille]

Hello.

 I will try to explain my problem clearly ...


 I've got a 25" zenith tube with a well's gardner p538 chassis.

 The problem is that when there is a lot of white at screen the vert/horiz sync go away for about half a second.

 I don"t know the good word to explain it..

 so here's a video of the problem (it can be clearly seen at capcom screen)




 I've tried to exchange the PSU with another cab PSU and the problem remains.

 My chassis taked a bath (lot of dust and spider webs) and i've checked visually it seems that there is no cracked solders.

 Tried 3 differents PCB and same problem.

 A cap kit is going to my home.

 Some people think that is a power related issue .. but i don't know how to test it.

 Any idea ?

 Thanks


Nb = i live in france (220volts)

[SirPeale]

I would definitely start with capacitors.  Bright screens like that can drain more than darker screens.  If the capacitors are "on the cusp" of failing, they can cause all kinds of different errors.

[lilshawn]

i would suspect the biggest cap on the board. it's kinda hard to tell in the video but it looks like the picture is all over the place (vary in size shape)


if this is the case, the capacitor your looking for will be about 400 volts... it will be the biggest one on there. It helps absorb and even out the power fluctuations caused by the screen going from dark to light to dark again.

but like SirPeale suggests, i would start replacing the capacitors on the board, it's quite and old chassis, and likely they are getting dried up.

[dapsaille]

Thanks to you two (i felled afwully alone in front of this problem) ^^

 A capkit is on the go.

 But i think that the 400v capacitor is not included in the cap kit ...

 For preventive reasons i will command it to my local reseller.

 And yes, the problem is that the screen vary in shape size.

 Hope this operation will permit me to close the backdoor of this cab, or my wife will throw it  

EDIT = i've found a 200v 560uf on the chassis ... a big one at an edge of the pcb .. is this the right capacitor ?

[Kevin Mullins]

EDIT = i've found a 200v 560uf on the chassis ... a big one at an edge of the pcb .. is this the right capacitor ?

Back on the back corner ?
HUGE capacitor ?
Location something like C55 ?

Yeah, that's it......order it separately.

[dapsaille]

Yes it is C55.

 I'm ordering it now .

 Thanks

[dapsaille]

Well .. the only reseller in France that i've found doesn't want to work with "personnal" people .. only companies ..

 May i use a 400v 560uf capacitor instead of a 200v 560uf ?

 Or maybee a 250v 560uf ?

 Regards

[Kevin Mullins]

Yes.
uf must be the same, voltage may be higher but not lower.

[dapsaille]

it's me again.

 I've just replaced capacitor C55 and did a capkit .


 Now the picture is more 'stable' .. i mean there is no more wave like before .. but the shape size problem is always here ...

 i've also noticed that i've got a magnetisation effect on the lower left side ... but the funny thing is that i've returned my monitor (and swapped sync in consequence) and the magnetised glow is always at the same place ... normally it would be at the top right after the screen return but no ... i've checked it seems that i haven't any source of magnetisation here .. i've moved my cab to another room for being sure that this is not a power cable in the floor or other trikky source of magnetisation but same ...


 and at the top of the screen i've got no scanline at all ... hard to explain .. seems that i've got a hugue scanline effect on all the screen but not in an area near the top ..

 this problem has followed the screen return too, so this is not a tube related issue.

 Does it tell you anything ?

 Does the THT (fllyback) may be responsible for the shape effect ?


 What will be the next step for making this crt work ?

 Will it rain today ?  

EDIT= i've followed the advice of a poster from another forum.

 It tell me to test the voltage of C57 .. i get 120 stable when i'm on a service menu; but when the monitor display white pictures it can go down to 90v .. is this normal ?


EDIT2 = What's a HOT please ? now i know flyback (THT in france for Très Haute Tension, Very High Voltage) but i really don't understand HOT .. thanks

[lilshawn]

HOT is.... horizontal output transistor

[dapsaille]

Thanks for the HOT definition.

 Does anyone ave any idea about this problem of white saturation ?

[grantspain]

contrast too high will cause it,also a fault on the abl circuit on the monitor
also please check the +5 on the jamma connector

[dapsaille]

I've checked my +5v and all is ok..

 It happens with a jpac too (who doesn't need jamma power)

 Do you know how can i check the auto beam limiter ?

[grantspain]

pretty sure the abl is controlled by the flyback on the k7000 series,try turning your contrast down first

[dapsaille]

If u put down the contrast the problem disappear ..

 But sort of unplayable .. i like to play with dark colors but ... it is too dark ^^

 May the flyback be the culprit ?

[Kevin Mullins]

You could try turning the SCREEN up on the flyback a tad, maybe the Brightness as well, but keep the Contrast down to balance the flicker.
A lot of games that do that sort of abrupt bright flash scene change stuff need adjusting to balance it out.

[grantspain]

take the colour gains down and adjust the brightness up

[dapsaille]

Yeahh ...
 

thanks for the tips .. it worked ^^

 But now i can see a problem who have already been described by other owner's of this monitor but without replys :/


 I cannot center horizontally my picture, there is a 4 or 5 cm (sorry didn't know in inches ^^) black border at the right .. if i try to adjust with horiz plot the picture come to right then i loose sync .. there is also a problem with focus .. center/bottom is near perfect except a color problem in the bottom/left corner but in the top of the screen focus seem blurred and at the top i've got a deformed picture ...

 hard to explain i will take a shot later.

EDIT = my color problem is caused by the flyback cable who touched the .. hemmm ... don't know the word ^^ the convergence ring .. who wasn't glued ..

 So i hope that with a little calibration all will be ok .. the question is can i do that with power on ?

[lilshawn]

you might have another problem....maybe bad capacitor or try to adjust horizontal position. sounds like you are adjusting horizontal hold.

the convergence ring set the alignment of the colors. (a white square would have separate red green blue colors at the edge of the square)

[Kevin Mullins]

sounds like you are adjusting horizontal hold.

I agree.... you shouldn't lose sync with positioning.
You should be adjusting the horizontal SHIFT.
There is also a Left, Center, Right positioning jumper that you can move fore more drastic shift.

You may be able to adjust the 50/60Hz pot on the main chassis for some of the deformed picture if it's at the top as you described. It's hiding behind the Horizontal Hold pot near the flyback.

[lilshawn]

There is also a Left, Center, Right positioning jumper that you can move fore more drastic shift.

if you do change this be sure to do it with the power off

[dapsaille]

Hi,

 yes i was adjusting horizontal hold  

 50hz/60hz plot cause me other problems than described.

 I've followed your recommandations and now my picture is perfectly centered and i've started to adjust convergence problem but alone it is difficult to do ...
 i will wait my wife for make a perfect convergence setup.


 I've moved the jumper from center position to right position and after that picture is ok ^^


 The last problem is that i've got a horizontal area near the top (about 10% of the picture) who don't have scanline .... or maybee 90% is overscanned ^^, this area take all the horizontal size of the crt and is clearly defined.

 This is not a tube related problem because i've rotated 180% the tube and problem persist at top.

 I've already changed all the caps (except 3 1uf who will be replaced next week) so do you have any idea for make this tube works flawlessly ?

  Thanks again for your advices.

[lilshawn]

if you could post a few photos of your problem and post them here, we can see ourselves and guide you in fixing it right.

i am having trouble understanding your explanation of your problem. I realize English is not easy for some people.

sorry but we will help the best we can.

a picture needs no explanation

[Kevin Mullins]

Yeah, I think I know what's being described, but seeing a picture of it would definitely help.