CRT Monitor Question

[JayTea]

Hello,

    I just bought a cab at an auction, and everything seems to work except the monitor, which has burn in from a keno game.  

     This was a missle command originally, and it has been converted a few times and is currently  "Thunderjaws", which is supposedly a jamma cab (I wouldn't know the difference, I need to research this more).

     I want to know if there is a way to fix/repair the burn-in?  I know I can do a cap-kit, but is this going to do anything to the burn in?

    Second, what are the leading causes for CRT monitors failing in a Jamma Cab?  I am not a circuit board / monitor guru (obviously), but if somebody can give me an idea on where to start, I am capable.  Maybe a bad tube?  A fuse? bad ROM chip?  I dunno....

    I want to get the game working to see how bad the burn in affects the screen during play, AND to see if I have a viable jamma cab to part-out, or run jamma-mame.  Thanks in advance!

[Carsten Carlos]

I want to know if there is a way to fix/repair the burn-in?  I know I can do a cap-kit, but is this going to do anything to the burn in?

Nope. No way. Never. The phosphor in the tube itself is burnt partly away, there isn't any chance to fix this.

[JayTea]

Nope. No way. Never. The phosphor in the tube itself is burnt partly away, there isn't any chance to fix this.

Damnit all to hell.  Well, I still want to see what the game looks like, even though Keno numbers will be in the background for a while  

[MameFan]

You know, if I had more time, I really should write a PINNED FAQ about monitors.  (Nothing bad about the poster, but it seems the same questions are asked quite a bit about monitors and it would be nice to have all the issues in one spot)

Anyway, if you scour this forum, you will find 2 recent posts by me regarding chassis swapping (keeping a good tube, but putting on a new electronic board rather than repairing a bad one)--that's in "dhansen"'s "Whooo mamaaa" thread.  Also a little about swapping tubes in one from last nite (I think the "sparkling" thread?)


In any case:
- No, you cannot ever fix burn in. The best you could do is give an overall burn in by negating the original image (e.g. this is what the Atari 2600 did in "screen saver" mode when left untouched after a while.. It didn't go black rather it pulsed the colors to then give an overall burnin instead of overburning certain spots).    Burnin is caused by electrons constantly burning off the layer of colored phosphor on the front of the tube.  Once "etched" your only hope is to replace the tube.

- Cap kits only affect the ability of the board to draw on the screen..usually horizontal or vertical deflection issues (eg a scrunched or overdrawn screen, wavy lines, bars on the screen, etc..) They cannot affect anything "within" the tube.

- While chassis (electronic boards) can fail for numerous reasons, tubes fail for only about 4 reasons typically:
a) Burnin.  Applies to television too, the difference is there, since the image is always moving you never see "etched" patterns, but if you look and an old tube close up you can easily see burned in tubes vs new ones.

b) Heater-to-cathode-shorts.  Basically metal particles fall off the shadow mask on the front of the tube during transport and if tilted fall on the gun portion, OR particles burn off the guns and fall back into them, shorting the "beams" with the "heaters" that keep them warm and ready to draw, causing an overall fog on the screen of a certain color

c) Loss of gun or focus or something else electronic-> (While can be caused by a board, swapping boards won't help). The metal on the guns or grids burn off and eventually cause them to fail.

d) Vaccuum loss.  A crack in the neck of the tube/around a wire into it.. Obiously the tube is now toast (and may even give a spectacular fireworks show when connected after it's lost the vaccuum)



To repair your phosphor damage, you just need to find a compatable tube (easy to find, harder to replace), or tube+yoke (easier to replace, harder to find) to pop into your chassis.

OR, you just find any old good tube+yoke, and buy a new chassis for around $75 shipped and reuse your existing frame but throw the bad tube and sell the chassis and yoke on eBay and pay for the new chassis! (Easiest option overall!)  

Again, rather than retype the world (until I get an FAQ done), read the "Whoooo Mamma" thread by dhansen and get more info there.

Good luck!

[JayTea]

Thanks for the info mamefan!

    I used the search feature with the keywords monitor and burn, and a lot of the topics that came back were CD rom burning-related.  I also had to use "any words" for my search, as "all words" produced only 1 topic, yet when I did find some relevant topics using "any words", both words were in the topic.  I have had similar dealings with the search feature here before, that's why I posted this thread.  Don't get me wrong, I love this forum - but that search engine is screwy sometimes.

     I will investigate my monitor more closely when I get a chance.  Now that I know what I'm potentially up against, I'm like James Brown..I feel good.  A CRT repair/troubleshooting FAQ would be awesome, if somebody has that much time.  I think the average Joe getting into this hobby has little or no experience working with CRT monitors - only you former TV repairmen have such knowledge and skill

[BobA]

Here is a link to the Whoooo Mama tread.  It was on the 2nd page when I looked so it is not too far back.

http://www.arcadecontrols.org/yabbse/index.php?board=4;action=display;threadid=5448

BobA

[JayTea]

Thanks BobA!  Clearly a lot of information to take in.  At least I know what I'm looking at inside my $20 cabinet.  $20 at an auction, can you believe it?  Everything powers up and works except monitor (I can hear the game being played), so I want to see if I can fix this beast.  


     I've seen some tutorials on how to discharge a monitor, but I think I'm just going to have a TV repairman do it (Pac Man isn't worth my life).  Having said that, am I in grave danger just REMOVING the picture tube (assuming ithe tube is the problem) from the cabinet?  Is there a "safe" way to remove it?  Thanks for the input.

JT

[MameFan]

Yes and Yes... But it's just like sitting next to an outlet with a screwdriver and a bowl of water... You can only hurt yourself if you don't know what you're doing

Discharging a monitor is easy (easier than teaching someone how to *properly* solder) BUT you must be aware of the issues and risks.

Simply HANDLING a monitor is nearly as risky as discharging it.  A wrong push against anything even close to the neck could cause an immediate implosion/explosion that will hurl glass and metal in every direction (while you drop the tube on yourself at the same time)

I will start working on an FAQ about arcade monitors to address these things.. otherwise just manually search the top 5 or so pages of posts here and you'll find many things like discharging and what not answered.  Also check out www.therealbobroberts.com as he has some safe discharging information too.

[JayTea]

I like the Bob Roberts homemade tool and writeup on discharging.  Looks like a tool that I'm going to be making and using more than once  

     I have a question regarding cleaning the chassis and PCB's - they are covered in 20 years of dirt, any suggestions?  I was going to just use my air compressor and blast it, but I was wondering if anyone had any luck with something else?  Thanks again everyone!

[radiator]

i'd use the air compressor with a hoover on the oposite side...that way, the dust that gets blasted off immediatly gets sucked into the hoover

if there are any parts on the PCB that have real nasty dirt (that wont blast off easily) - try using a soft cloth and some isopropyl alcohol

*m

[MameFan]

>   I was going to just use my air compressor and blast it, but I was wondering if anyone had any luck with something else

I wouldn't use a high PSI air compressor.  At most, what a can of compressed air can put out only.  Too high of pressure and any grain of sand against the neck of the tube could mean a very very bad result.

Also, you do NOT want to remove the black graphite coating that goes around the tube... that's integral to how it works (technically it's one of the two capacitance plates)  You can however wipe the thick black "attracted" dust from it.


Basically, when I clean a monitor, I use a vaccuum with bristle nozzle and wipe around everything except the neck. Use it on the circuit board too.   Then I take pre-moistened wipes (clorox, others in the round tubes or rectangular boxes---they dont disintegrate like paper towels do), and wipe of all the back of the tube and edges of components on the board/wires/etc.

Again be VERY careful around the neck, perhaps just use a q-tip with cleaner on it there.  Don't bump the 8 ring magnets behind the yoke or the wires leading to/around the yoke (you make break one) and dont put much pressure on the tube neck.

You can safely do this with the monitor unplugged and NOT discharged but still fully connected to the circuit board.  It's actually safer than removing the cap from the tube and dealing with it that way as the tube can "gain" a charge just sitting in the air.  A properly working chassis will keep it grounded when off so no charge is built up.

[paigeoliver]

You forgot to mention exactly what the monitor is doing (or not doing).

Is it even hooked up? Is the fuse blown?

Does the neck light up? If not, then you may be replacing the flyback.

There may be a switch on it for input voltage, if this is set wrong then it won't work (had a game with a "dead" monitor once that worked just fine after I switched that switch).