Credit for this post is to: RetroHacker
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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.
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.

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.

Deflection failure:

Now, I already talked about what the deflection circuits are, and what they do. But how do they work? Well, it's basically an amplifier - driving the yoke coil rather than a speaker voice coil. The signal gets generated by oscillator circuits (or, in a vector monitor, the game board), and amplified by transistors. The two deflection circuits are seperate. If one of them fails, you lose deflection along that axis, thus the image gets compressed down to a single line. Be careful when this happens - turn down the brightness to prevent burning the tube. In a raster monitor, the horizontal oscillator is pretty tightly tied to the flyback and the high voltage. But, in a vector monitor, the deflection circuits are completely separate from the high voltage circuits - as they simply amplify the signals from the game board and aren't tied to a particular frequency.

The most common cause of lost deflection isn't the failure of the amplifier - it's usually a solder joint. Most notably, the solder joints on the yoke connector, and sometimes on the output transistors themselves. Check these first. In the Electrohome G07, a common failure is FR401, which is a fusible resistor in the vertical deflection circuit.

It's also very possible to have improper deflection, or foldover. The image will literally look like someone rolled up or folded over one side of it. This is usually a capacitor failure, and cured with a cap kit. It's also possible to lose one of the vertical transistors and only have half the screen scanned. In XY monitors, it's even possible to lose one quadrant of the screen.

If you're having deflection problems, first determine wether it's horizontal or vertical deflection that you've lost. Remember, always think of the monitor as being oriented like a television set. A vertical line on a vertical game like Ms. Pac is really a failure of the vertical circuit in the monitor - not the horizontal.


And, since I've thought about it, now is as good a time as any to bring up...

Identifying Components:

Circuit boards and schematics usually have letters and numbers associated with components. Each individual part has it's own name, like C401 or R634. The name of the part will tell you about it - the first letter tells you what kind of component it is, and the first number usually helps to identify which circuit or section it's in. For example, I know that in the Electrohome G07, all the components in the vertical circuit are in the 400's. So FR401 is a fusible resistor in the vertical circuit. The letters mean:

C - Capacitor
D - Diode
F - Fuse
J - Connector
L - Inductor
P - Connector
Q - Transistor
R - Resistor
S - Switch
T - Transformer
U - Integrated Circuit (chip)
V - Tube
W - Jumper
X - Crystal (or sometimes a Transistor)
Y - Crystal
VR - Variable Resistor (potentiometer)
FR - Fusible Resistor
CR - Diode
IC - Integrated Circuit (chip)
JU - Jumper
SW - Switch
ZD - Zener Diode

This is not an exhaustive list, but it's all that I could think of off the top of my head. I'll go back and add to it if I think of any more. Note that some letters mean the same thing as other letters - just depends on the manufacturer. Similarly, some letter codes may mean different things - I've seen boards where VR meant Voltage Regulator. Also, to make things even more confusing, sometimes the board isn't even labelled correctly. On earlier WG6100's, there was a zener diode labelled as R, and on the Electrohome G07 there's a cap with the polarity printed wrong on one side of the board.

Now, these component letter codes are pretty universal - but when it comes to logic boards which are mostly IC's, the chips are numbered differently. The board will actually have letters printed down one axis, and numbers printed down the other. Chips are then reffered to with a letter-number code, specifying the row and column. So, if something tells you to check the chip at E5, then you know where to find it. Longer chips that extend across multiple rows or columns take more hits to sink... er... I mean, are usually referred to by the first position they occupy.


And, while we're on the subject of components, let's touch on polarity:

Some components have no polarity - it doesn't matter which way they're installed. Resistors are a good example. Most other components, however, do have polarity. Electrolytic capacitors, which you'll probably be replacing a lot of, are marked as to which lead is positive and which is negative. Usually it's a stripe down the side marking the negative. Similarly, the board is usually marked - but don't always trust it. Sometimes it's marked wrong. The G07 has one cap that's marked correctly on one side of the board, and wrong on the other. So when replacing parts, pay close attention to the way the original part was installed. Don't install caps backwards. When an electrolytic is powered backwards, it won't function, and it also tends to explode, or at least vent out the top. Even if it doesn't, don't re-use it if possible. If you accidentally put an electrolytic in backwards, and power it like that, it's safe to assume that it has been damaged, and it should be replaced.