Basic monitor information - how to ask good questions. Read this first

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Basic monitor information - how to ask good questions. Read this first

So, you've got a game with a monitor issue. Where to start? Start by finding out some basic information about your monitor, and about your problem. It's very hard for us to be useful when presented with the question "My Ms. Pac has a lousy picture, how do I fix it?". While that may be a valid question, it doesn't have enough information. It's like saying "My blue car won't start".

Things that are very helpful in determining the solution to your problem:

- The kind of monitor you're talking about. There are dozens of different arcade monitors. It's very, very helpful to know which one you need help with.

- The game you're using it in. Some games have different monitor connections than others (positive vs. negative sync, etc).

- What is the monitor doing or not doing? A picture helps here sometimes, but a good description is even better.


How to identify a monitor:

For the most part, raster video game monitors are all pretty much compatible. A monitor from a Ms. Pac will work in Defender will work in Street Fighter, etc. Because of this, it's very common for monitors to have been swapped throughout the life of a game. Not only that, the manufacturer didn't necessarily use the same monitor throughout the entire production run of a game. They used whatever was available and cheapest. So, just because you have an original Robotron or whatever, there's no guarantee that the monitor that's in your original game is the same as what's in mine. The only way to tell is to look at the monitor.

Exceptions to this are Nintendo monitors - those are pretty much always Sanyo 20EZ's. And with vector monitors there are only a couple of types. If you have a vector game, then you've got one of like five monitors.

Look at the back of the monitor. Learn to identify the basic components. The picture tube is the large glass thing that the image is displayed on. This tube is NOT going to be unique to a specific monitor. The numbers on the tube only identify the tube itself, so they aren't helpful in identifying the monitor. The deflection yoke is the coil of copper wire that goes around the neck of the tube. These all physically look very similar - but it's good to know what the yoke is when working on monitors. The chassis is the circuit board that sits beneath the picture tube, and has all the electronics on it. It'll have a flyback transformer - that's the large block with the thick wire coming out of it. That wire connects to the anode of the picture tube with a suction cup. That's the high voltage - don't disconnct this without discharging first, or it'll hurt :). The monitor's frame is usually where you'll find the identifying marks - but sometimes also stuck to the side of a piece of metal on the chassis. It'll say something like Electrohome G07 or WG19K4900 or somesuch. That's the model of the monitor. That's the vital piece of information.

It's not uncommon for these tags to fall off though. So, if you can't find it, there are a couple of ways to identify your monitor. Go to http://www.therealbobroberts.net/monitor.html for a bunch of pictures of monitor chassis. Try to match up what you have. The ones at the top are the most common ones.


Basic monitor gotchas:

DON'T disconnect the HV anode without discharging it first! The picture tube stores a charge, and it can zap you good if you're not careful. To discharge, take a cliplead and attach one end to the monitor's frame, and the other end to the shaft of a plastic-handled flat blade screwdriver. Slide the screwdriver under the suction cup untill you feel it touch the metal contact in the center. If the tube still had a charge, you'll hear a nice POP! You don't need to discharge the tube unless you need to disconnect that anode lead. And watch out, sometimes the tube can sort-of recharge itself, just enough to startle you. Do it again just to be safe.

DON'T connect a monitor directly to a wall socket! Most game monitors are "hot chassis", and as such require an isolation transformer. Plugging such a monitor directly into a household wall socket will fry stuff. This especially includes Nintendo monitors. They have a standard looking wall plug on the cord, but that's meant only for the 100v isolated socket in the bottom of the game.


About screen burn:

Monitor screen burn is a fact of life when it comes to arcade machines. These games were running for many, many hours, and some of them display the same thing most of the time. This leads to screen burn. Basically, a monitor displays an image by drawing an electron beam across the face of a glass tube, the inside of which is painted with colored phosphor. When the beam hits the phosphors, it excites them, and they glow - i.e., they emit their own light. Over time, if the same phospor areas are constantly bombarded with electrons, and constantly glowing, they'll start to wear and darken. They develop a brownish tinge, and emit less light. This area of the screen is now "burnt", and will remain darkened like this forever. You can't unburn a picture tube any more than you can unburn toast. The only way to fix it is to replace the picture tube.

Medium resolution:

Some newer games use what's known as a medium resolution monitor. This monitor has a higher scan rate, and higher screen resolution. Medium resolution games are not compatible with traditional standard resolution monitors, and vice-versa.

Can I use a computer monitor?

Short answer: No. Long answer? Nnnnoooooooo.
The scan rates are incompatible. While converters do exist, the cost of them far exceeds the costs of repairing or replacing the monitor properly, and the picture quality will never be as good as a real arcade monitor.

What about LCD's?

They do make arcade resolution compatible LCD's. They're very expensive, and don't look as good as a real monitor. Similarly, there do exist converters to convert arcade video to VGA - they're also very expensive, and it'll look like garbage. Also, putting an LCD in an 80's arcade game is considered a sacralige, much like cutting up a 1957 Chevy to shoehorn a modern engine into. And once you've seen a game so converted, you'll understand exactly why people feel that way. It looks terrible.

Hopefully this helps you understand a little about game monitors, and enables you to ask helpful questions. We're always happy to help and answer questions... but hearing the same thing a hundred times gets a bit old. Once you know your monitor's model, you can always search this forum for more information on your problem.

I'll also be adding to this thread, with basic problems and terminology explained.

-Ian
 
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Monitor repair is not something to be taken lightly. You should have a fair understanding of electricity before attempting to repair your arcade monitor. Do a little bit of reading on the internet. Things you should understand are the difference between AC and DC voltage, diodes, resistors and capacitors. Know how to recognize these parts and roughly what they do. Monitors do contain high voltages - and it's important that you understand what you're doing.

Discharging a monitor, and why you have to:

The flyback transformer generates the high voltage needed to accellerate the electrons toward the screen. This is in the vicinity of 20,000 volts. It is very low current, but it is high voltage. Modern flybacks contain built-in diodes to rectify the inherent AC output of a transformer. Now, most DC power supplies have a capacitor across the outputs to help smooth out the DC that the rectifiers create. A flyback circuit is no exception. However, in this case, the capacitor is the picture tube itself. One plate of the capacitor is the conductive outer coating of the tube, known as aquadag, or "dag" for short. In an arcade monitor, this is always grounded. That springy strap that goes across the back of the tube ensures that this coating is grounded to the metal frame of the monitor. The second plate of the capacitor is the inner coating of the tube. This is where the flyback's anode connects to - through that little hole int the side of the tube. The glass the tube is made from becomes the insulator. This combination acts as a large capacitor, and does store a charge. What you're doing when you discharge the tube is shorting out this capacitor, causing it to release it's stored charge all at once (hence the zapping sound).

Some monitors have built-in bleeder resistors to bleed off this stored charge when the monitor is powered off. Many do not. For safety's sake, always discharge a monitor before disconnecting the HV lead. Also, after the monitor has been discharged, it's possible for a tube to build up a small charge again, due to reasons that I won't bother going into. So, even though the anode lead has been disconnected, it's sometimes still possible to get bitten by the tube itself. So, discharge, disconnect, re-discharge after thirty seconds or so. That second charge is very minor, but it sure will suprise the heck out of you!


Adjusting the colors:

There are several adjustments on an arcade monitor to adjust the colors. On the neckboard (the little board that plugs into the neck of the picture tube), there are a number of controls. These adjust the cutoff and drive to the picture tube guns. Some monitors have a full set for all colors, others only have controls for two colors. Their purpose is to adjust the gun signals to compensate for variation between the guns. On the flyback, there are two knobs, one labelled FOCUS, and one labelled SCREEN. The focus knob does just that - it focuses the picture. The screen control acts almost like a brightness control, boosting the screen voltae at the picture tube. Turn it up too far, and you'll see retrace lines. Too low, and the picture will be dark.

To adjust your monitor, first dial in the focus. Adjust the control until the image looks uniformly sharp. Then, adjust the screen control - turn it up so that you see the haze, then back it down so that the haze goes away and your black areas are black. Adjust the individual color controls for the best color - turn them up too far and the colors bleed and smear. Sometimes it helps to turn up the screen control to get that haze while doing this. You want to be able to get white haze - not tinted haze. The idea is to get all three guns at the same output level, so that whites are white.


But the picture is distorted/washed out/crummy!:

Then you might be due to replace the electrolytic capacitors in your monitor. Over time, these capacitors dry out and function poorly. Sometimes they can leak too. Electrolytic capacitors look like little cylinders, and are all over the monitor's chassis. It's pretty common practice with these older monitors to simply change all of them at one shot, since they're all 20 years old or older at this point. This is known as a "cap kit". To order a cap kit, you must determine the model of your monitor, and order the kit from Bob Roberts, ArcadeShop, Zanen Electronics, or other arcade supplier. Alternatively, you can write down the values of the individual components and order them from Mouser or any other electronic supplier. Problems usually solved by cap kits:


- folded over picture
- smeared, faded colors
- distorted picture
- dim lines in picture
- touchy sync


But my monitor is totally dead!:

Then you probably don't need just a cap kit - although now is as good as any to install one. Search out information on your specific monitor, this will help you repair it. Check the fuses on the chassis - usually failure of one of these is the result of some other, more serious failure elsewhere. You probably have a shorted semiconductor, blown flyback, or something else. See listing of incredibly common monitor failures, in a post below.

What's this B+ I keep hearing about?:

B+ is the name given to the main power supply voltage in a monitor. It's name goes way back to battery operated radios, and the origin isn't important here - but remember that it's the main DC power supply voltage. It's exact voltage varies from monitor to monitor - you'll have to check the manual for your monitor to find out what it should be, but it's usually around 120v. For the Sanyo 20EZ, it's 108v. For the Electrohome G07, it's 120v. For the WG6100, it's 180v. This voltage is adjustable on many monitors, but not on others (WG4900, for one).

So... how does this B+ supply work, anyway?:

Glad you asked (even though I know you didn't). For a usual color raster monitor: Isolated AC enters the monitor chassis from the isolation transformer. This is 120vAC (100vAC for the Sanyo). It goes through the main chassis fuse, and occasionally a line filter. From there, it gets rectified by four big diodes, and turned into DC. This DC is then gets filtered by a big capacitor (usually 680uf at 200v or similar, it's the biggest one on the chassis). After that, it usually goes through a fuse, then into a transistor based circuit containing the voltage regulator transistor and a large ceramic resistor. At the output of this circuit, there is usually a marked test point - or you can just test at the output side of that resistor.

And I test it... how?:

Set your meter to DC volts. Put the black lead on the metal frame of the chassis, and the red lead to the B+ test point for your monitor. This test point may be a labelled point on the board, or it may be one side of the large ceramic resistor - check your monitor manual. If your monitor has an adjustable B+, dial it in using the control. It's important that the B+ be set correctly. Running it too high will result in a picture that's too large, and could cause the monitor to go into shutdown to prevent the HV from going high enough to generate X-rays through the picture tube. Too low can cause a small picture, waves of distortion in the screen, or image instability.


To be continued...

-Ian
 
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Incredibly common monitor failures, sorted by monitor.

Electrohome G07:

No picture, monitor is dead. Small fuse on chassis is blown.

The flyback had died, and it took the horizontal output transistor with it (2SD870). This is so common, that most people replace these flybacks even if they still work. Replacement parts are inexpensive and easy to get, and a whole kit including the flyback, HOT, fuses, and all the caps is available from Bob Roberts as a rebuild kit. Replace the HOT, and flyback, and you should have your picture back - but you might as well replace all the capacitors while you have the chassis out. Don't forget to adjust the B+ after rebuilding!


Picture too small, there's black space on all sides.

The B+ voltage is too low. It should be 120v. You can adjust this with the control on the chassis - but do it while measuring that voltage. Get it as close to 120v as you can.


Won't sync well to negative sync, but works fine on positive?

You're going to like this one... Check resistors R314 and R317. They're supposed to be 390 ohms. At some point, Electrohome goofed and fitted 4.7k's here. These only affect the negativ sync circuits, not positive. So if the monitor was used in a positive sync game, this problem would never have presented itself.



Sanyo 20EZ:

The top of the picture is all curled over!

Capacitor C407 has gone bad. It's right near the flyback, and it's 10uf @ 160v.


The picture has hazy dim lines through it, they look like the bars of a jail cell!

Time for a cap kit. Lots of caps can cause this - when it gets to this point, it's not worth trying to pinpoint the problem.


I have this wavy bar rolling through the picture.

Either your B+ is too low (should be 108v), or the main filter cap is bad. If you've adjusted the B+ and it's still wavy, replace that cap. It's the large one, C606. 470uf @ 160v



WG K7000:

We've actually got a sticky dedicated to this one... read that too!

Arcing, zapping noise, fuzzy picture, or clicking with picture distortion/flicker:

Look at the flyback. If it has white knobs, it's time to replace it!



To be added to later...

-Ian
 
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Is any of this useful information to anyone, or is it just too long and nobody is going to bother to read it?

-Ian
I read everything so far and am stuck to it like a tween reading a twilight book!

Currently I am planning on checking the b+ voltage on my g07 and possibly adjusting it! Since mine is slightly cut off on top and bottom (vertical centipede setup) that is assuming its got a g07 in there,haven't looked at it recently enough!
 
Currently I am planning on checking the b+ voltage on my g07 and possibly adjusting it! Since mine is slightly cut off on top and bottom (vertical centipede setup) that is assuming its got a g07 in there,haven't looked at it recently enough!

Probably does, I've seen several Centipede's with G07's.

To adjust the B+ on a G07, connect the black lead to the montior's frame. Red lead goes to the end of the large ceramic resistor closest to the picture tube. The adjustment pot is laying flat on the chassis, behind the vhold pot. You're looking for 120v.

If it still won't fit on the screen after doing that, you may have to adjust the width coil. The width coil on a G07 is the white plastic tower in toward the front of the chassis, in front of the flyback. The width coil on a G07 is a notorious weak point. Be VERY careful adjusting it, as it's very brittle. If it breaks, you'll have to replace it. Turn a width coil ONLY with a PLASTIC tool. Never metal. You used to be able to get plastic adjustment tools at Radio Shack, but I don't know if they still carry them.

A width coil is essentially a variable inductor. When you adjust it, you're actually moving a ferrite slug up and down in a threaded plastic form, moving it in and out of the magnetic field of the coil. The problem is that this ferrite is brittle, a metal tool will break it. Also, the plastic form is very brittle from age and heat. Start slowly, try to work the slug back and forth a bit to get it freed up. Never adjust a coil to it's extremes, it shouldn't take that much tweaking to get it in line.



A note on vertical vs. horizontal monitors:

Some games (like Centipede, Ms. Pac, etc) use a vertically mounted monitor. Other games (Defender, Popeye, Berzerk, etc.), use horizontally mounted monitors. The difference between them is... nothing. The monitor electronics are exactly the same. They're just mounted sideways for vertical operation. When referring to monitor adjustments, the controls always refer to standard horizontal orientation (like a television set). So, if in Centipede, your high score and stuff is off the screen, then to adjust it, you need to adjust the width of the picture, not the height.

Some monitors have a metal frame that holds the tube vertically, but again, these are no different than a horizontal monitor - the controls on the chassis still refer to dimensions in terms of a horizontal orientation. The chassis in a vertical monitor is identical to the same chassis used in a horizontal one. Interestingly enough, most vertical games actually just use a standard horizontal shelf-mount monitor, mounted sideways, rather than a monitor with a vertical frame.

-Ian
 
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I called for one of these the other day. I got my wish. christmas in july? ;)

now it needs the sticky treatment. good stuff, very thorough.
 
Very nice! I feel like a sponge, got any more coming?
 
Thanks for the positive comments guys. Glad to be helpful. I had actually written most of the first post a week or two ago, but hadn't posted it because I was still working on it. Then I saw mecha187's suggestion for a "basic info" thread, and figured that now was as good a time as any to clean it up and post it. :D

-Ian
 
Awesome info Ian! I didn't want to post in your thread and ruin the flow, but since others are doing it! ;)

Nice work- I've bookmarked it for future reference!
 
Deflection basics:

What is deflection? Well, first, a little bit about the basics of CRT displays. The inside face of the picture tube is coated with phosphors in three colors, already discussed earlier when I talked about screen burn. Slightly behind the face of the tube is a metal grille, known as the shadow mask. It looks like a cheese grater - staggered tiny holes. You can't see it from the outside of the tube (you'd have to disassemble it to see it, and by disassemble, I mean "break with a hammer"), but trust me, it's there. Then, at the neck of the tube, is the electron gun assembly. This contains three separate electron guns, that are driven by the monitor electronics. The tube is filled with a vacuum (that is to say, not filled at all...).

So, the monitor electronics drive the electron guns to emit pulsed streams of electrons. There are three guns, each aligned with a particular set of colored phosphor dots. Electrons travel very nicely in a vacuum, and left to their own devices, leave the guns and travel directly straight ahead. This is great if you just want a tiny dot of light in exactly one place, but we'd much rather have them be able to light up the whole screen with a picture. That's where the deflection circuits come in. On the neck of the tube is a rather largeish coil of copper wires. This is the deflection coil, more commonly known as the yoke. The yoke actually contains two independent sets of coils - one for horizontal, and one for vertical. If you were to take the yoke apart, you could see the separation.

Now, electrons in a vacuum are affected by a magnetic field. They're deflected by it. So, by applying a signal to the separate coils of the yoke, the yoke creates magnetic fields that bend the stream of electrons and change the area of the face of the tube that they will hit. In a typical raster monitor, this beam of electrons deflected by the yoke and is scanned across the tube, from top to bottom, left to right, painting a picture as it goes. Imagine it like a REALLY fast printer. The electron beam is only touching one tiny point of the tube at a time, but since the phosphors stay lit for a while, and our eyes themselves have a certain persistence to them too, we see a stable, unmoving image. When in reality, only a tiny fraction of the screen is being written to at a time. This is why, when you record a video of a CRT display with a camera, you sometimes see this band of darkness waving through it. That's because the camera can capture things faster than the eye can, and it's catching the electron beam.

When the beam gets to the bottom of the screen, it's shut off, and the magnetic field is changed to bend it back up to the top. This takes a very tiny amount of time, but it's known as the "blanking interval". But, the beam isn't truly turned off all the way, it's still there, just with not enough energy to light anything up. But when you turn the SCREEN control on the flyback all the way up, it causes that "blanked" beam to be visible, resulting in the angled retrace lines on the screen.


What about vector monitors? Those are different, right?

Yes. They are. In a raster monitor, the deflection electronics are fixed at a particular pattern and frequency. They scan the tube exactly the same way, all the time, and synced up to the game board's signal via the sync line(s). Vector monitors, on the other hand, have no sync line. Instead, the deflection circuits are directly controlled by the game board. Vector games can manually bend that beam of electrons anywhere on the screen at any time, turn the beam on, then bend it someplace else, and shut it off again - allowing a perfectly straight line to be drawn from one point to another. It's the difference between coloring in squares on graph paper and drawing free-form. Vector monitors are thus different from raster monitors because they have these deflection amplifiers with direct inputs.


And how does convergence fit into all this?

Convergence is the alignment necessary to get the red, green and blue "beams" to converge at the same spot on the screen. Those three beams are separate, and need to be aligned so they work together. First adjustment is actually purity. Purity is the ability for a particular beam to ONLY hit it's proper color, and not "miss" and hit the wrong colored phosphors. Then, the convergence must be set up to align the beams with each other. Convergence is achieved by the way of tiny little magnets, mounted on movable rings, right between the electron gun and the deflection yoke. Basically, to "prebend" the beams of electrons, to get them lined up, before they're bent all together to scan the face of the tube. These tiny magnets can affect (mostly) only the one particular color since they're right next to the guns. But getting them aligned is a royal pain, and is outside the scope of this guide.


You said something about a shadow mask?

Yes. And I almost forgot. The shadow mask is basically a stencil. A piece of metal designed to ensure that the electron beams don't "spill over" onto the wrong dots on the screen, and only hit one at a time. This shadow mask sometimes gets slightly magnetized, however, and it bends the electron beams as they pass through, causing them to miss their mark! This causes a psychedelic colored picture. When this happens, the tube must be "degaussed", which is just a fancy way of saying "demagnetized". A picture tube is very sensitive to magnetic fields, including the Earth's magnetic field. Usually, when you move a monitor, it must be degaussed. Because this degaussing is so important, all color monitors and televisions have built-in degaussing coils. That's the fat (usually black, sometimes grey) cable that snakes around the back of the tube near the face. It looks like it was wrapped in lots of tape. It's another magnetic coil - and it gets fired for a second or so every time the monitor is turned on from being cold. That's the "thooom" sound that some monitors make on powerup. Sometimes, the shadow mask gets too magnetized for the weak little coil in the monitor to clear it up. Multiple cold powerup cycles can help it, but other times you need to degauss it manually with a handheld degaussing coil. Also, it IS possible for a strong magnetic field to permanently magnetize or even bend the shadow mask. Similarly, a tube that was dropped hard enough can bend or dislodge the mask. If this happens, there is no repair short of replacing the picture tube.


-Ian
 
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Nicely done! One comment though....I thought the flyback's purpose was to simply remove the spent electrons from the tube. I didn't think it had anything to do with helping the electrons accelerate towards the face of the tube....at least that's my understanding of how monitors work. Either way it's great to see something like this written. It'll be a very good resource to beginners so they can post better informed questions. Maybe add some pics to illustrate some things? :)
 
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Nicely done! One comment though....I thought the flyback's purpose was to simply remove the spent electrons from the tube. I didn't think it had anything to do with helping the electrons accelerate towards the face of the tube....at least that's my understanding of how monitors work.
I'd never heard that before. From my understanding the anode actually does accelerate the electrons toward the screen. Technically, there are two anodes in a picture tube - one is the focusing anode, the other is the accelerating anode. The flyback creates voltages for both, through the divider network (bit with the knobs on it). Focus voltage is something like eight hundred volts, second anode voltage is twenty thousand. Electrons exit the gun and are attracted to the focusing anode, then get forced through the focusing anode by the greater pull of the accellerating anode.

At least, that's how I always understood it. I may very well be wrong. Of course, the precise innerworkings of the picture tube hardly matter from a repair standpoint, but it's nice to have a basic understanding of what's going on inside that bulb.


Either way it's great to see something like this written. It'll be a very good resource to beginners so they can post better informed questions.
Thanks! I hope it's helpful. I tend to be a bit long-winded, so I hope people aren't just immediately offput by how long it is...

Maybe add some pics to illustrate some things? :)

Hehe... I should probably take a picture of a monitor and label all the components, at least.

-Ian
 
The flyback's other function is to supply other voltage levels necessary for the operation of the monitor outside of the HV, heater, screen, and focus. The voltages necessary to operate vertical deflection for example are obtained from a tap on the flyback transformer.

If you are missing a power feed inside the monitor, check the appropriate tap on the flyback. There will typically be a resistor (think fuse!) and a high speed diode along with a capactor to smooth the voltage out. If the cap is blown the diode will be shorted. If this is the case look for a crispy resistor too.
 
How about going back and titling different topics or sections in bold to help people navigate or differentiate?

And add this:

If you end up fixing your monitor, please post what the final solution was in your repair thread. It will help others who have a similar issue...
 
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