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

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.
-Ian
Agreed. The place I learned a lot about monitor repair was from Randy Fromm's books and DVD's (podcasts in my case). He even mentions that knowing exactly how it works isn't as important as understanding how it fails and how to fix it. I have to agree there. I have a much better understanding than ever on how they work, but more importantly, what to look for in fixing them.
 
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...

+1 but for all repair threads

I hate pulling up a thread from 2 years ago with my exact problem, but it's left hanging without a resolution (of course maybe there wasn't one). I always try to go back to my threads when I get the problem solved and post what I did to fix it.
 
I am glad I have you around to fix my monitors, and everything else for that matter. There is no way I would remember all that!! Great info Ian.

You guys would crap yourselves if you know how old Ian is. It still amazes me how much he knows for such a young Jedi.
 
Thanks again for all the positive comments. I'm glad that someone is actually reading all of that. And I hope that this can be useful to people starting out. I know it's long, but learning takes patience, as does monitor repair, for that matter.

And thanks for the suggestions - I've gone back through and bolded the section headings.

Repairing anything begins with logical deduction. Understand what the device is supposed to do, what it's doing wrong, and then begin thinking about how to attack it. Start with the simple things, and work your way through it. If you understand HOW something works, you can break it down logically, and test things in order. If your car won't start, you don't begin by replacing the engine - you first check to make sure there is gas in it. Similarly, if your game is dead, you start at the power supply and work your way through it.

And, speaking of breaking things down logically - how about determining if you have a monitor problem or a game problem? Some game board failures actually look a lot like monitor failures - especially with black and white games. So...

A word on black and white raster monitors

Very old games use black and white raster monitors. Games such as Space Invaders, Sea Wolf, Atari Football and Breakout. These monitors are similar to their color counterparts - but they're also a lot closer to television sets. These monitors actually take standard composite video.

So, what this means, is that if you have a problem with a black and white game, and you want to rule out the game board, you can connect the game's video output to a modern television or an old composite video monitor, and verify that it's working. Likewise, you can connect a known working device, such as a Nintendo or a VCR, to the game's monitor, and verify that it is working properly.

Look at the wiring diagram for your game. The monitor has a single molex plug that carries both power and video. Note that black and whtie monitors don't need isolation transformers, they have transformers built-in. Two of these pins in the connector carry the video signal, and should be marked as Video and Video GND or similar on the wiring diagram. Be sure you have the correct wires!

To connect this to a TV set, the video signal goes to the center pin of an RCA connector, and the video ground goes to the outer ring of the RCA connector. You can make up a simple test lead, with an RCA connector on one end, and some bits of stiff wire (like from a paper clip) soldered to the other end. The stiff wire can be inserted into the back of the Molex connector so that it touches the proper pin inside the housing.

To test the game on another screen, leave the plug disconnected from the monitor. The monitor has a terminating resistor on the video line, if two are connected at once, the picture will be dim. To test the monitor with another device, plug the connector into the monitor, and disconnect the edge connector from the game board.

-Ian
 
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.

-Ian
 
Omg!

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

I am right there with ya! This thread is very helpful. Keep it coming. Got any info on a Sharp Image SI-319? My Horizontal width coil is non function and I can't seem to find a replacement, although I doubt the problem is actually the coil.
 
Excellent thread. I have a few basic questions that made me curious after reading. Hopefully it can help others too.

1)You mentioned discharging only if you are removing the anode cap. What if you want to transplant the monitor to another cabinet with the anode still in tact? (Not real familiar with this but perhaps you have to disconnect the anode to swap a monitor?) Should you always just discharge the monitor just to be safe if you have to work on it?

2)What parts of the monitor should you never touch while on or off to avoid shock?

3)Is it safe to adjust the monitor adjustment knobs with your fingers while on or is it best to use an insulated screwdriver? I know someone who was seriously zapped adjusting the color balance and they dont recall touching any other component (perhaps there was an arc)?
 
1)You mentioned discharging only if you are removing the anode cap. What if you want to transplant the monitor to another cabinet with the anode still in tact? (Not real familiar with this but perhaps you have to disconnect the anode to swap a monitor?) Should you always just discharge the monitor just to be safe if you have to work on it?
You really only *need* to discharge the monitor if you intend to work on it. I.e., remove the chassis from the tube. If you're moving the entire monitor, there is really no reason to discharge. You wouldn't think of discharging the tube on your television to move it from one room to another. That said, you can if you want to, it's not going to hurt anything.

2)What parts of the monitor should you never touch while on or off to avoid shock?

Never touch the high voltage connection while the monitor is on. Also, be very careful of touching the back of the neckboard if it's not covered. Most monitors, from the factory, have cardboard or plastic zip-tied to the back of the neckboard to insulate it, but this often goes missing. The G2 and focus connections are made at the neck of the tube, and it's possible to get an unpleasant shock from them if the solder points on the back of the neckboard are exposed. Also, avoid touching any metal-cased transistors on the main chassis.

When the monitor is off and unplugged, you only need to be mindful of discharging the picture tube, as well as any large capacitors on the monitor's chassis. The large filter cap mostly - it'll be the biggest one on the chassis. Be careful removing the chassis so you don't touch it's contacts with your fingers. Discharge this by shorting across it's terminals on the bottom of the board - I usually use a needle-nose pliers. Just open them to the width of the cap's terminals, and touch the points of the pliers to the cap. You don't want to accidentally discharge that cap into yourself or into other parts of the chassis.

3)Is it safe to adjust the monitor adjustment knobs with your fingers while on or is it best to use an insulated screwdriver? I know someone who was seriously zapped adjusting the color balance and they dont recall touching any other component (perhaps there was an arc)?

Yes and no. Any controls with plastic knobs are safe to adjust with your fingers, including the ones on the flyback. Some monitors, like the G07, use very simple metal controls for things like height, vhold, etc. Not only are these almost impossible to adjust with your fingers - you probably shouldn't. Use a little screwdriver. Any ferrite core that needs to be adjusted should be done ONLY with a plastic tool (width coils, mostly). Others you can use a metal tool on as long as you're careful not to short out nearby stuff.

I routinely adjust controls with my fingers on monitors.. but if you don't feel comfortable with that, use a screwdriver.

Use common sense. Don't go blindly poking around in a monitor with your fingers if you don't know what you're doing. Limit yourself to touching things that are designed to be touched - like user adjustable controls with plastic knobs. The yoke is also safe to touch, as well as the convergence rings - you'll have to be touching these a lot to do convergence setup.

If you're hunting for a cold solder joint, a good technique is to poke and wiggle things on the chassis to see what changes operation. Do this with a plastic ballpoint pen barrel or something non-conductive.

And remember - getting shocked hurts. It can hurt a lot. But the sort of current available in a monitor is very unlikely to kill you. Just use common sense, and don't touch anything you don't understand, and you should be fine.

-Ian
 
Excellent thread. I have a few basic questions that made me curious after reading. Hopefully it can help others too.

1)You mentioned discharging only if you are removing the anode cap. What if you want to transplant the monitor to another cabinet with the anode still in tact? (Not real familiar with this but perhaps you have to disconnect the anode to swap a monitor?) Should you always just discharge the monitor just to be safe if you have to work on it?

You really only *need* to discharge the monitor if you intend to work on it. I.e., remove the chassis from the tube. If you're moving the entire monitor, there is really no reason to discharge. You wouldn't think of discharging the tube on your television to move it from one room to another. That said, you can if you want to, it's not going to hurt anything.

I've got three comments to make about this (I skimmed through this, so apologies if some of this was mentioned earlier):

1) It IS possible to be shocked by a monitor when moving the entire thing. I had a monitor that I was pulling from a Centipede. I discharged it before pulling it. Then discharged it again while it was on the floor in front of it. Then I picked it up with the tube against my chest (so I wouldn't accidentally break the neck) and started carrying to my work bench. About halfway there - BAM - I got a huge electrical jolt right through the chest. It felt like a defibrillator had hit me. A buddy was there and saw it happen, and still doesn't know how I kept from dropping the damn thing. The television analogy isn't good because the TV usually has a plastic (non-conductive) case around it that you are holding on to.

2) Monitors can also regenerate a small electrical charge after being discharged. It is not uncommon to discharge a monitor, remove the chassis, and then have a small spark when you go to reinsert the chassis, so alway discharge again before you reinsert the anode cup. Hell, I had a monitor sit on the floor for a month and still have a charge when I went to work on it.

3) Monitors from the K7000 and newer have self-discharging circuits that will discharge the monitor safely when powered down. This is why you rarely see any spark when discharging them. This does make it more likely that you can move them safely without discharging. But don't take it for granted. If your monitor has problems (even if it still works), it's possible that the self-discharging will not work properly (or at all) and you will still get shocked if you don't discharge. I always make it a point to discharge before I ever put my hand near the hole. And you can discharge it and leave the anode cup in the hole. No need to remove it...
 
Last edited:
Fantastic thread! This is very helpful to me as a total video rookie trying to fix my Atari Football.
Thanks for posting this thread!

Chris
 
great resource!

"And how does convergence fit into all this?"

at the end of the section , add in some references to sections of particular books/manuals, such as this the G07 manual!
 
This is great to have this info in a sticky. Id love to see more things like this so i can learn more about things. I know Mod has mentioned in another thread that we need to have a place to put things like this but dont really want to have a whole page a stickies to go thru. Keep up the good work guys.
 
I found it useful as I have three monitor chassis I am trying to work on. There are some other generic questions I have that as a noob I'd love to have answered:

Is there a way to test capacitors with a multimeter or some other method?

How do you check resistors? What about things like the HOT or Vert IC?

What would cause capacitors to "pop", is that a generic issue or something more specific to a monitor?

Many thanks to anyone who can clear this up for me
 
Is there a way to test capacitors with a multimeter or some other method?

Some meters have a capacitance setting, but it typically only measure small value caps, and you're required to insert the legs into openings on the meter. This doesn't help when the legs have been trimmed short. I've made some jumper wires that plug into my meter that I can connect to the cap legs.

But in order to test them properly, you really need an ESR meter.

How do you check resistors? What about things like the HOT or Vert IC?

Resistors are simple. Just set your meter to the OHMS setting, choose the closest value that is HIGHER than the reading you are expecting, and then put your leads on opposite ends. You can't always test it in-circuit and get a good reading, so you'll need to unsolder one end and pull it out of the board to get a good reading.

HOT's are transistors, and can be measured like one - using the diode test on your meter. Google how to test transistors if you need more info.

A Vert IC or other IC with multiple legs can sometimes be tested via the diode test (if they do that function internally), but may need a logic comparator or IC tester to test them properly.

What would cause capacitors to "pop", is that a generic issue or something more specific to a monitor?

Capacitors pop for a variety of reasons - old age, installed backwards, etc - but the basic reason is that more voltage is applied to the capacitor than it is rated to handle (or has aged to the point that it's value is lower than what it should be). It fills up too quickly and explodes before it can discharge (in general terms).

This can happen on monitors, power supplies, etc. If you get a big enough surge (like a lightning strike), it will blow lots of parts, not just caps...
 
Some meters have a capacitance setting, but it typically only measure small value caps, and you're required to insert the legs into openings on the meter. This doesn't help when the legs have been trimmed short. I've made some jumper wires that plug into my meter that I can connect to the cap legs.

But in order to test them properly, you really need an ESR meter.



Resistors are simple. Just set your meter to the OHMS setting, choose the closest value that is HIGHER than the reading you are expecting, and then put your leads on opposite ends. You can't always test it in-circuit and get a good reading, so you'll need to unsolder one end and pull it out of the board to get a good reading.

HOT's are transistors, and can be measured like one - using the diode test on your meter. Google how to test transistors if you need more info.

A Vert IC or other IC with multiple legs can sometimes be tested via the diode test (if they do that function internally), but may need a logic comparator or IC tester to test them properly.



Capacitors pop for a variety of reasons - old age, installed backwards, etc - but the basic reason is that more voltage is applied to the capacitor than it is rated to handle (or has aged to the point that it's value is lower than what it should be). It fills up too quickly and explodes before it can discharge (in general terms).

This can happen on monitors, power supplies, etc. If you get a big enough surge (like a lightning strike), it will blow lots of parts, not just caps...

Thanks for answering my questions, that is very helpful!
 
OK, here's some info that I wrote up and wanted to post, but figured it wasn't really all that necessary. But, since people are asking about *why* caps fail, I figured it might be interesting to some. It's definitely more info than you need - all you need to know is that caps fail with age and should be replaced, but if you want to know how they work, then here's a brief overview.

The secret life of electrolytic capacitors:

What is an electrolytic and why is it polarized? Why do these caps fail with age? Why is it they're usually blue? All good questions... well, except for that last one. That's just silly :)

First - the principle behind a capacitor. Two plates, separated by an insulator. A charge builds up on one plate, and is stored. Then, it discharges through the insulator to the other plate. In this way, a cap can smooth out a signal, block DC, and lots of other useful things. Normal capacitors, such as the ceramic disc types, have no polarity. Their plates are both the same. But, ceramic and plastic caps of this type have small capacities - less than 1uf usually. Electrolytic caps are special - they have polarity and higher capacities.

A typical electrolytic capacitor consists of two long thing strips of aluminum, sandwiched with a strip of paper soaked in a conductive electrolyte. The aluminum strips are the plates, and the insulator is actually a layer of aluminum oxide on one of them. The electrolyte soaked paper is not an insulator - but rather electrically becomes part of one of the plates. The leads are crimped into the aluminum foil, and everything is rolled up and stuffed into an aluminum canister, with a rubber plug sealing the bottom, allowing the leads to stick out.

The polarity of this type of capacitor is very important because of the thin aluminum oxide insulating layer. If you power the cap backwards, the reverse voltage will break down and destroy the insulating oxide layer, causing a short. This causes the cap to heat up and sometimes explode.

Modern electrolytics are provided with a scored vent in the top. This is to allow a "safe" release of pressure should they short or overheat. The vent will bend and split and release the gasses formed by the broken-down electrolyte. Occasionally you'll see a cap bulged up at this vent, or split. This is an obvious indicator of a damaged capacitor that must be replaced. Some older electrolytics have no such vent, or a different sort of vent. These usually vent out the bottom, or simply explode. It's also not uncommon to have a cap that has pushed the rubber plug partway out of the bottom.


That's all well and good - why do caps fail with age?:

Ah... that all has to do with that electrolyte solution. It's exact composition varies between manufacturers, but it's basically some kind of weak acid or solvent, usually mixed with ethylene glycol and water. In other words: oily goo. The capacitor's body is supposed to be sealed, but the electrolyte is rather corrosive in and of itself, and the main seal in the cap is a rubber plug crimped into an aluminum tube. Over time, this leads to the electrolyte evaporating, breaking down, and otherwise going away. The less electrolyte, the poorer one of the plates conducts, and thus the "capacity" of the capacitor decreases. In circuit, it no longer performs as it did when it was new. Also, because the plate doesn't conduct like it should, the effective resistance through the cap increases, and thus the voltage drop across the cap increases. Not good.

So, I can just replace the ones that are bad?

You could. Just so long as you like working on the same monitor over and over again. Some people like to use an ESR meter to find the caps that have started to fail or have failed - checking to see which ones have high effective series resistance. This will identify the bad caps, and then you can replace just those, and the monitor will work again. But for how long? Who knows. You could have gotten a couple of exceptionally good caps that'll last forever. But chances are, the rest of the 25 year old capacitors aren't far behind in their quest to dry out their electrolyte, and now that the monitor is running again, they'll sit there, slowly cooking away... They might last a week, a year, forever? Who knows. But the simple fact remains that electrolytic capacitors DO have a service life, and they do fail with age. Might as well just replace all of them while you're in there - the small ones in monitors are not expensive.

That means that capacitors have a shelf life?

They sure do. The manufacturer generally specs ten years of shelf life, or something like that. Effective service life seems to be something like 25 years... but it really depends on the application. Sure, a capacitor that's been sitting doing nothing for 20 years is more likely to work than one that's been stuffed in a hot flyback cage in a running game for the same length of time... but a brand new component is likely to last much longer.


-Ian
 
Back
Top Bottom