Monitor Wei-ya '21, the brightness does not hold

[marcelosofth]

Hello friends, 

I have already done several types of tests, suspecting that it was my PC, Video Card, but the problem continues, the image is perfect in colors, contrast and brightness, but when a high brightness image comes or the screen totally full the brightness drops to 30%, something unacceptable, my last suspicion is that the monitor can not withstand a Cinescope of '21 inches and only one of '20 normal, is it?

Ps. See the 2 images below, with the black-bordered screen the image is perfect in its fullness of brightness, contrast and color, but when it fills the wilted brightness. 

[buttersoft]

I answered you in the GM forum first, because i didn't see this post, but have moved my reply here instead. The Wei Ya is not a good quality chassis, and is almost certainly having the problem i describe.
.
.
.

Normally a chassis (the electronics) designed to drive a 14” CRT tube can drive a 19”/20” tube without a problem, but there are many exceptions. You won’t have any trouble changing from 19” to 21”, or at least not of the kind you’re seeing.

There are two main causes for your problem. The first is that you have a good brand of chassis but it's old, and the caps are drying out somewhere. This is not very likely outside a PC chassis, as you would normally see other problems with geometry as well.

The other cause is more probable. This is what i think is happening, but i'd be keen to hear from some of the experts. I am guessing you have a cheaper, newer universal chassis. These are all that is made now, you cannot get anything else new. They used to be a bit better, but the ones now are bad. Unfortunately there is no market for expensive chassis anymore. One problem with these cheaper chassis is that they normally have a very low beam current limit. This is to compensate for a lack of control in other areas, and it stops you burning your tube and giving yourself too many x-rays, among other things.

The beam current limit is the total power going across the screen grids (total current from cathode to anode) and represents the total power of the image you can produce, and it cannot get very high on these universal chassis. An image on a small area can be bright, but a complete picture cannot. There is no way to fix this, you can change the heater resistors, but it won't do much. If you play with the individual colour settings you can get the brightness changes to change colour as well, but either way you cannot get more power to the tube - any attempted changes in this area will start to distort the picture and will probably damage the chassis in other ways. The best you can do with one of these universal chassis is to find a high-quality tube that remains in good condition, but this may not help much.


Finding an old chassis that is compatible with your tube might be the best idea, and Nanao's are pretty much the best arcade chassis. Another option might be to RGB hack an old TV, as these are normally stronger and better than the universal chassis.

[marcelosofth]

Many thanks friend, with your response.

So, unfortunately here in Brazil it is not easy to find a Monitor, we have to import and it is very expensive value, I managed to buy even if I paid dearly these 2 monitors Wei-ya and now I have to work miracles with them and try to be happy ...

See how curious, I bought a TV '21 LG brand, and did the mod RGB by the Neckboard, you believe that gave exactly the same identical problem with the drop in brightness in full images, I could not believe, so with all tests and experience that I got I really get the latter option that the problem is in feeding a '21 kinescope, and I'm almost sure that testing with a 20's kinescope will not happen, if this is confirmed I will have to conform to using one of '20 curved, and let my will that was to use one of '21 flat ... 

[buttersoft]

The Wei Ya chassis are known to be weak, but the neckboard mod doing the same thing is a bit weird. Normally tapping into the neckboard directly will remove the feedback circuit that controls the beam current, which also bypasses the HV regulation (i'm not yet convinced that doing this is a good idea in the long term, though i realise the mod works.) It could be that the HV is dropping with the neckboard-modded set.

[Paradroid]

Normally tapping into the neckboard directly will remove the feedback circuit that controls the beam current, which also bypasses the HV regulation (i'm not yet convinced that doing this is a good idea in the long term, though i realise the mod works.)

Yeah... the Jungle IC is usually doing a lot of work to take care of all that. Tapping the Jungle is a cleaner mod because you're only hijacking the OSD input rather than interrupting other aspects of the TV's function.

I have seen the the kind of dimming you're talking about. Sometimes it's too do with a poor design (as in butter's explanation) and sometimes it's to do with failing components (e.g. I have seen one Blaukpunt do it while another identical model did not).

Lowering the contrast fixed the issue on a Philips 25" I modded. With high contrast, the shotgun blast in Metal Slug would temporarily dim the image (after the screen flashed white). Totally fixed by dropping the contrast.

[marcelosofth]

I am now in search of a '20 inch tube to prove my thesis that these 2 monitors I have of Se-Cai can not feed full screen the 3 tubes that I have and that I tested ...