Can any CRT veteran help with this?

[Lobotomika]

I moved house a couple months ago and the process left my retrogaming CRT TV with nasty scratches in the middle of the screen. I liked that TV so I replaced it with another of the same model but this one is second hand and there's a problem I didn't have with my old TV. Brand is BEKO, screen is around 22" (55 cm)

Bright areas get distorted and slightly enlarged and whenever a horizontal line has more number of bright pixels than the others, it's displayed in a wider area so the screen is never vertically smooth at the sides. Very distracting with some demos when screen flickers.

There are no relevant options in the service menu and I'm not sure if it's a dying tube, a bad board or a mix of both. I'm considering swapping motherboards but I'm not sure if I'll be forced to recalibrate the tube afterwards. I have some experience operating TVs so I'm not expecting to die this time either.

Maybe there's a way to fix this with some tinkering, what do you say?

I'll post photos tomorrow, it's getting late for that right now.

Thanks for reading

[Lobotomika]

Can any mod move this to support.other or support.hardware? This is the screen I'm using with my Amiga. It's not really as off topic as I initially thought and no one reads it here.

[Hewitson]

You've probably got a bad cap in the power supply. If you decrease the brightness does it still happen?

If you swap the chassis over, you won't need to do any adjustment to the tube.

[pandy71]

Or dried caps or this CRT is not good - if i understand correctly your problem there is pumping effect for high brightness? or perhaps there is blurring.smearing on high brightness details with some dark halo behind ?

For pumping issue blame insufficient HV current source (HV trafo + multiplier is underpowered). If second then to high level signal can be a problem (i.e. there are two video level standards - first where black is 0.0V and white 0.7V, second where black is same 0.0V but white is 1.0V - when display is 0.7V but white is 1.0V then it can be situtation where amplifier is saturated and remain in this state for a time - in that case just switch sensitivity to 1.0V if this is possible).

[Lobotomika]

Thanks for the replies! Sorry I totally forgot about the photo so here it is: (both are the same TV - the newly acquired one)



I placed a horizontal rectangle in the middle of the screen with deluxe paint and it distorted the vertical one; also got itself distorted. Also in the second photo you can notice the waves that appear when the screen displays a solid color.

I'm having very interesting looking trees in Sonic 1 first zone with my Mega Drive

None of the caps are out of shape but I don't have a multimeter around. Do you think tinkering with the focus controls on the trafo will help?

Reducing the brightness reduced the effect and well, that's about it. I'm going to call the service tomorrow as it's still an actively supported brand and will ask them to make one working CRT out of the two.

[kipper2k]

On some old TV/monitors there are 2 adjustments that can be made on the flyback transformer, one is for sharpness and the other is for brightness. See if you have those adjusters on yours. if you do, adjust them... HIGH Voltage... be careful

[lesta_smsc]

Not sure if this is of any relevance, but it talks about correcting lines on CRTs:

http://www.edaboard.com/thread256211.html

[Lobotomika]

Originally Posted by kipper2k

On some old TV/monitors there are 2 adjustments that can be made on the flyback transformer, one is for sharpness and the other is for brightness. See if you have those adjusters on yours. if you do, adjust them... HIGH Voltage... be careful

Yup, I got those and I know I can lose a finger Just wondering if that'd be relavant to my problem. I don't want to defocus my tube for no reason.

[zipper]

That distortion might be a sign of overloaded power delivery/voltage sag.

[john1979]

Looks like same problem explained here

http://eab.abime.net/showthread.php?p=870963

Yes, it is CRT TV power supply regulation problem. It is not a fault (unless there are dried out capacitors)

Sudden big brightness change makes power supply to work harder (The brighter the image, the more current electron gun needs) and usually power supply can't handle it quickly enough = output voltage gets lower temporarily.

Lowered voltage = deflection coils can't deflect electron beam correctly = scanline's geometry and/or width changes.

[Loedown]

If you give me the model number or better still the chassis number I can most likely dig up a circuit. I can give better advice from that.

I would look at the brightness resistor, usually a big wire wound one in the order of 1 - 10 meg ohms along with the 1 - 10 uF cap on the neck board usually 250 - 400 volts rating. Measure B+ rail and check for arc marks on any of the blue capacitors in the line stage usually near the flyback transformer / tripler / high voltage pack. Sometimes they will have a blue arc that's visible. Don't adjust flyback brightness pot until you've verified everything else, high brightness on that usually results in retrace lines.

[Hewitson]

If decreasing the brightness improves the image, then it may be worth trying to decrease the brightness until you get an acceptable picture and then increasing the screen voltage on the flyback to compensate.

Of course, there's not much point in doing this when you have a perfectly working spare chassis sitting there.

[roy bates]

if you have one that works properly and one that doesent you have a reference point on the working one.

[Lobotomika]

Thanks a lot to everyone who replied here. Very cool advices yet reading through them, I don't think my experience is sufficient to be able to do them myself. Still, thanks.

I sent both CRTs to service today; it'll probably save time, won't cost much and be safer this way however -gonna go a bit off topic here- I can't ignore that everyone, including the repairperson turned a critical eye over me since I intended to have a CRT repaired. Made me feel like I belonged to a religious sect no modern person would take seriously. :/ It's already impossible to find new CRTs in 2013, opposed to like, just five years ago and I can't imagine what the situation will be like in 5 years. I already have a 47" 3D LED TV I'll desperately want to replace in 2 years and I'm apparently, still an outcast in this consumerist world. (is that a word?) I just love how capitalism works; makes you feel like a terrorist for having a hobby.

@loedown, if you still have too much time and are still interested here are the circuits:

scratched one

newly bought second hand with the problem mentioned

Your input will probably be more accurate than the halfhearted repairman and I'll have the upper hand to deal with the situation if you can find something out of these circuits.

[roy bates]

theres nothing wrong with owning a crt set,ive still got a few.
im not a fashion follower.

[Lobotomika]

Originally Posted by roy bates

theres nothing wrong with owning a crt set,ive still got a few.
im not a fashion follower.

We need to fight back in style:

[roy bates]

thats awsome.

[Loedown]

B+ is 107V and you can take a reading from TP237

C707 would give the bright / over smeary picture 10uF 250V on neck board.

Good luck with your repairs.

[lesta_smsc]

Originally Posted by Lobotomika

We need to fight back in style:

I can't possibly see how that is all suspended by itself! Impressive!

[ElectroBlaster]

Had the same Beko 24" crt in the living room until it started playing up one day. Bought it in 2004 and then combined that with an SN45GV2 shuttle pc. Loved it because it could do proper RGB via scart so was perfect for an HTPC hooked up including everyting else. Very good pin sharp image, was gutted when it finally went bad!

I then brought it into our bedroom and had an amiga and atari st on for a while but it started getting worse. Wanted to get it fixed but no engineer was bothered. Had the same old answer "Buy new!"

List of symptoms:

Bowed picture but not all the time
Shrunk picture, again not all the time
Sometimes nasty smells (Assumed it was Ozone mixed with burning?)

The smell was enougth to give up at the point as we got paranoid of fire hazards etc.

I hope you can get yours sorted