21 inch CRTs and sharpness.

JMEaT · Post by **JMEaT** » Sun Feb 20, 2005 9:45 pm

Got a quick Q about big CRTs. I just picked up a 21 inch Phillips and I noticed the picture is sharper around the edges than in the center. It does this at any resolution any color depth. Is this normal of bigger CRTs? Or is something FUBAR? Overall the picture isn't 100% sharp, kinda slightly hazy but only in windows, you don't notice it in games or in movies.

Thanks

Krom · Post by **Krom** » Sun Feb 20, 2005 10:45 pm

Focus. I had to adjust both my NEC 930SB monitors. With CRTs there are a couple pots near the back left of the monitor on the inside, adjust them with a small screw driver till the monitor has a more uniform sharpness. Beware, the pots are very touchy, a small movement will blur the entire screen, you want to use some sort of test pattern a screen full of 8 point text will do the job.

Most monitors have three pots in the back, two are focus (horiz/vert) and the other one is power, if the monitor brightness is where you want it _do not_ touch the power screw. They are as touchy as the focus screws and can turn your screen totally white or black instantly, then it takes forever to tweak the monitor back to the proper brightness.

You might have to take the cover off the monitor to do this, and it has to be done with the monitor on. Be extremely careful, theres 10-20kvolts inside the case and even if the monitor is off they still hold a charge. Do not touch anything other then the screws you want to turn. Both of my NEC monitors have holes in the side of the case so you can adjust the focus without taking the covers off, check and see if the 21" has the same.

JMEaT · Post by **JMEaT** » Mon Feb 21, 2005 9:31 pm

I don't have any knobs on the outside... and I'm guessing opening it would void my warrenty

WarAdvocat · Post by **WarAdvocat** » Tue Feb 22, 2005 8:03 am

Don't be a poussy! DO IT

JMEaT · Post by **JMEaT** » Tue Feb 22, 2005 8:18 am

That's a low blow, mister!

*Gets out screwdriver*

woodchip · Post by **woodchip** » Tue Feb 22, 2005 9:58 am

Wait a minute...aren't all the controls for such things through the control panel?

Krom · Post by **Krom** » Tue Feb 22, 2005 10:12 am

Not the focus controls. Some stuff can only be done by the rings on the back of the tube, but don't do those at home, thats professional service only. The power and focus pots are easy and safe enough to do at home.

WarAdvocat · Post by **WarAdvocat** » Tue Feb 22, 2005 10:56 am

In all seriousness, this post contains good info. I have a 17" Viewsonic which blurs slightly in the very center.

I'll be whipping out my screwdriver PDQ

AceCombat · Post by **AceCombat** » Tue Feb 22, 2005 5:01 pm

im never opening a CRT based device again in my life.

i had a bad experience with CRT's.

*i think ive already laid this incident out on here, but its been awhile so here it is again*

i had a small 3' B/W dual power tv that my mom had in the basement in the junk box. so i grabbed it out of the box and took it upstairs out to the garage. i opened up the case and started getting curious as to what parts did what. well i noticed this large black suction cup attached to the side of the tube with a much larger wire leading back to the flyback transformer. i grabbed a flathead screw driver and started to pry that cup off.............................

ZZZZZZZZZZZAAAAAAAAAAAAAP!!!!!!!!!!!!!!!!!!!!!!!

i was blinded by what could be described as "The holy white light" for about 30 seconds.... after i regained my sight, i smelled burning metal, plastic and fiberglass. i looked at the smoldering screwdriver in my hands only to discover that the metal itself had vaporized about halfway up the shaft and was slowly melting the plastic handle. of which at that same moment, it got hot in my hands so i dropped the handle.

i grabbed some heavy duty rubber gloves and promptly tossed the tv into the trash.

Krom · Post by **Krom** » Tue Feb 22, 2005 5:26 pm

Thus concludes AceCombatâ??s daily lesson in stupid and how to spot stupid people.

REDDER · Post by **REDDER** » Tue Feb 22, 2005 7:21 pm

The experience ACE reflect the warnings issued when it comes to opening and messing around the inside of TV's.

It seems that the coils that drive the tube hold somewhere around 50,000 volts or more or something like that.

The warnings used to tell one to beware of replacing parts in a TV unless the capacitors that delivered the voltage to the tube were properly discharged.

If one accidentally shorts the capacitor or any wire connected to the capacitor... you basically got a instant lesson in welding. Like ACE did.

So if you remove the cover from your CRT be careful where you poke around

MD-2389 · Post by **MD-2389** » Tue Feb 22, 2005 7:54 pm

REDDER wrote:It seems that the coils that drive the tube hold somewhere around 50,000 volts or more or something like that.

15,000VAC for black and white and 30,000VAC for color.

If one accidentally shorts the capacitor or any wire connected to the capacitor... you basically got a instant lesson in welding. Like ACE did.

No kidding.

Ace is lucky he's still alive. DAMN lucky. Though this would explain why he was so angry when he first showed up.

So if you remove the cover from your CRT be careful where you poke around

And don't be a dummy! (ACE) If you don't know what you're doing or what you're mucking with, leave it alone. At the very least have someone that knows TV repair nearby so they can tell you what you can and can't touch. Matter of fact, its a good idea to have a second or third person nearby just incase you do get a lesson in what tens of thousands of volts really feels like.

JMEaT · Post by **JMEaT** » Wed Feb 23, 2005 2:35 pm

Yeah...yeah... I just sent the monitor back.

woodchip · Post by **woodchip** » Wed Feb 23, 2005 5:50 pm

I got 2 used NEC tv's...same make and model. Took both of them to a local t.v. repair place and for 80.00 they swapped parts and tuned up one of the sets so it works great (had it 2 years now). So why would I want to fiddle in the back of of a killer voltage trap when for 80.00 a pro will do all the work.

Warlock · Post by **Warlock** » Thu Feb 24, 2005 8:04 am

y spend 80$ when i can just take 20min to open it and turn a few nobs

JMEaT · Post by **JMEaT** » Thu Feb 24, 2005 9:02 am

Why waste a perfectly good warranty when there is no guarantee that will fix the issue? O_o

AceCombat · Post by **AceCombat** » Thu Feb 24, 2005 3:04 pm

REDDER wrote: The warnings used to tell one to beware of replacing parts in a TV unless the capacitors that delivered the voltage to the tube were properly discharged.

one would think that 3 years of sitting in a box with absolutely no power supplied in those 3 years, would be enough for those capacitors to discharge themselves?!?!?!

If one accidentally shorts the capacitor or any wire connected to the capacitor... you basically got a instant lesson in welding. Like ACE did.

No kidding. Ace is lucky he's still alive. DAMN lucky. Though this would explain why he was so angry when he first showed up.

SHADDUP!!!!

Krom · Post by **Krom** » Thu Feb 24, 2005 3:17 pm

I've heard of the capacitors holding a charge for 10 years.

AceCombat · Post by **AceCombat** » Thu Feb 24, 2005 3:28 pm

really?!?! oooookay.

hey krom, got any ideas on the topic i just made?

woodchip · Post by **woodchip** » Thu Feb 24, 2005 8:24 pm

Warlock wrote:y spend 80$ when i can just take 20min to open it and turn a few nobs

Nice try. Parts had to be swapped. Loose parts had to be resoldered and color guns had to be calibrated. Slighty more than turning a few knobs.

MD-2389 · Post by **MD-2389** » Thu Feb 24, 2005 10:13 pm

AceCombat wrote:really?!?! oooookay.

hey krom, got any ideas on the topic i just made?

Ace, let me put it to you this way. I had in my possession a flashlight that had no battery. It used Lens' Law to generate power. (magnet moving through a coil of copper wire, thus generating a current charging a capacitor which lit up the light) I didn't even fully charge the sucker, maybe half power, and the damn thing stayed on all night long and still had enough power to light the LED. Even if theres nothing to discharge the capacitor relatively quickly (like an LED), the energy bleed-of would be so minimal that it would take several years like Krom mentioned. It all depends on two factors: How large the capacitor is and how much charge has been placed on it. I've personally seen 10ÂµF (thats micro-Farad or 10x10^-6 Farad) capacitors hold a full charge for over a month. Thats a very small capacitor compared to the larger ones you'd find on a CRT monitor motherboard. I think you get the picture.