Don't start with the electronic test equipment, start with some analytical thinking. Your powers of observation (and a little experience) will make a good start. Your built in senses and that stuff between your ears represents the most important test equipment you have. However, some test equipment will be needed: * Multitester (DMM or VOM) - This is essential for checking of power supply voltages and voltages on the pins of ICs or other components - service literature like the SAMs Photofacts described elsewhere in this document include voltage measurements at nearly every circuit tie point for properly functioning equipment. The multitester will also be used to check components like transistors, resistors, and capacitors for correct value and for shorts or opens. You do not need a fancy instrument. A basic DMM - as long as it is reliable - will suffice for most troubleshooting. If you want one that will last for many years, go with a Fluke. However, even the mid range DMMs from Radio Shack have proven to be reliable and of acceptable accuracy. For some kinds of measurements - to deduce trends for example - an analog VOM is preferred (though some DMMs have a bar graph scale which almost as good). * Oscilloscope - While many problems can be dealt with using just a multimeter, a 'scope will be essential as you get more into advanced troubleshooting. Basic requirements are: dual trace, 10-20 MHz minimum vertical bandwidth, delayed sweep desirable but not essential. A good set of proper 10x/1x probes. Higher vertical bandwidth is desirable but most consumer electronics work can be done with a 10 MHz scope. A storage scope or digital scope might be desirable for certain tasks but is by no means essential for basic troubleshooting. I would recommend a good used Tektronix or HP scope over a new scope of almost any other brand. You will usually get more scope for your money and these things last almost forever. My 'good' scope is the militarized version (AN/USM-281A) of the HP180 lab scope. This has a dual channel 50 MHz vertical plugin and a delayed sweep horizontal plugin. I have seen these going for under $300 from surplus outfits. For a little more money, you can get a Tek 465 100 Mhz scope ($400-700) which will suffice for all but the most demanding (read: RF or high speed digital) repairs. * A video signal source - depending on what type of monitor you are repairing, you may need both computer and television signals. Computer Monitors - a test PC is useful as a video source. Of course, it will need to support whatever scan rates and video types the monitor is designed to accept. Software programs are available to display purity, convergence, focus, color, and other test patterns. Or create your own test patterns using a program like Windows Paint. See the section: "Using a PC as a monitor test pattern generator". Studio monitors - a baseband video source like a VCR or camcorder is useful in lieu of a test pattern generator. These will allow you to you to control the program material. In fact, making some test tapes using a camcorder or video camera to record static test patterns will allow you full control of what is being displayed and for how long. * Color bar/dot/crosshatch signal generator. This is a useful piece of equipment if you are doing a lot of TV or studio monitor repair and need to perform CRT convergence and chroma adjustments. However, there are alternatives that are almost as good: a VHS recording of these test patterns will work for TVs. A PC programmed to output a suitable set of test patterns will be fine for monitors (and TVs if you can set up the video card to produce an NTSC/PAL signal. This can be put through a VCR to generate the RF (Channel 3/4) input to your TV if it does not have direct video inputs (RCA jacks). Sophisticated (and expensive) universal test pattern generators are available that will handle any possible monitor scan rate.
These are the little gadgets and homemade testers that are useful for many repair situations. Here are just a few of the most basic: * Series light bulb for current limiting during the testing of TVs, monitors, switching power supplies, audio power amplifiers, etc. I built a dual outlet box with the outlets wired in series so that a lamp can be plugged into one outlet and the device under test into the other. For added versatility, add a regular outlet and 'kill' switch using a quad box instead. The use of a series load will prevent your expensive replacement part like a horizontal output transistor from blowing if there is still some fault in the circuit you have failed to locate. * A Variac. It doesn't need to be large - a 2 A Variac mounted with a switch, outlet and fuse will suffice for most tasks. However, a 5 amp or larger Variac is desirable. If you will be troubleshooting 220 VAC equipment in the US, there are Variacs that will output 0-240 VAC from a 115 VAC line (just make sure you don't forget that this can easily fry your 115 VAC equipment.) By varying the line voltage, not only can you bring up a newly repaired monitor gradually to make sure there are no problems; you can also evaluate behavior at low and high line voltage. This can greatly aid in troubleshooting power supply problems. Warning: a Variac is not an isolation transformer and does not help with respect to safety. You need an isolation transformer as well. * Isolation transformer. This is very important for safely working on live chassis equipment. Since nearly all modern monitors utilize line connected switchmode power supply or line connected deflection circuits, it is essential. You can build one from a pair of similar power transformers back-to-back (with their highest rated secondaries connected together. I built mine from a couple of similar old tube type TV power transformers mounted on a board with an outlet box including a fuse. Their high voltage windings were connected together. The unused low voltage windings can be put in series with the primary or output windings to adjust voltage. Alternatively, commercial line isolation transformers suitable for TV troubleshooting are available for less than $100 - well worth every penny. * Variable isolation transformer. You don't need to buy a fancy combination unit. A Variac can be followed by a normal isolation transformer. (The opposite order also works. There may be some subtle differences in load capacity.). * Degaussing coil. Make or buy. The internal degaussing coil salvaged from a defunct color TV or monitor doubled over to half it original diameter to increase its strength in series with a 200 W light bulb for current limiting will work just fine. Or, buy one from a place like MCM Electronics for about $15-$30 that will be suitable for all but the largest TVs and monitors. Also, see the section: "Degaussing (demagnetizing) a CRT".
It is essential - for your safety and to prevent damage to the device under test as well as your test equipment - that large or high voltage capacitors be fully discharged before measurements are made, soldering is attempted, or the circuitry is touched in any way. Some of the large filter capacitors commonly found in line operated equipment store a potentially lethal charge. This doesn't mean that every one of the 250 capacitors in your TV need to be discharged every time you power off and want to make a measurement. However, the large main filter capacitors and other capacitors in the power supplies should be checked and discharged if any significant voltage is found after powering off (or before any testing - some capacitors (like the high voltage of the CRT in a TV or video monitor) will retain a dangerous or at least painful charge for days or longer!) The technique I recommend is to use a high wattage resistor of about 100 ohms/V of the working voltage of the capacitor. This will prevent the arc-welding associated with screwdriver discharge but will have a short enough time constant so that the capacitor will drop to a low voltage in at most a few seconds (dependent of course on the RC time constant and its original voltage). Then check with a voltmeter to be double sure. Better yet, monitor while discharging (not needed for the CRT - discharge is nearly instantaneous even with multi-M ohm resistor). Obviously, make sure that you are well insulated! * For the main capacitors in a switching power supply which might be 100 uF at 350 V this would mean a 5K 10W resistor. RC=.5 second. 5RC=2.5 seconds. A lower wattage resistor can be used since the total energy in not that great. If you want to be more high tech, you can build the capacitor discharge circuit outlined in the companion document: "Testing capacitors with a multimeter and safe discharge". This provides a visible indication of remaining charge and polarity. * For the CRT, use a high wattage (not for power but to hold off the high voltage which could jump across a tiny 1/4 watt job) resistor of a few M ohms discharged to the chassis ground connected to the outside of the CRT - NOT SIGNAL GROUND ON THE MAIN BOARD as you may damage sensitive circuitry. The time constant is very short - a ms or so. However, repeat a few times to be sure. (Using a shorting clip lead may not be a bad idea as well while working on the equipment - there have been too many stories of painful experiences from charge developing for whatever reasons ready to bite when the HV lead is reconnected.) Note that if you are touching the little board on the neck of the CRT, you may want to discharge the HV even if you are not disconnecting the fat red wire - the focus and screen (G2) voltages on that board are derived from the CRT HV. WARNING: Most common resistors - even 5 W jobs - are rated for only a few hundred volts and are not suitable for the 25KV or more found in modern TVs and monitors. Alternatives to a long string of regular resistors are a high voltage probe or a known good focus/screen divider network. However, note that the discharge time constant with these may be a few seconds. Also see the section: "Additional information on discharging CRTs". If you are not going to be removing the CRT anode connection, replacing the flyback, or going near the components on the little board on the neck of the CRT, I would just stay away from the fat red wire and what it is connected to including the focus and screen wires. Repeatedly shoving a screwdriver under the anode cap risks scratching the CRT envelope which is something you really do not want to do. Again, always double check with a reliable voltmeter! Reasons to use a resistor and not a screwdriver to discharge capacitors: 1. It will not destroy screwdrivers and capacitor terminals. 2. It will not damage the capacitor (due to the current pulse). 3. It will reduce your spouse's stress level in not having to hear those scary snaps and crackles.
You may hear that it is only safe to discharge from the Ultor to the Dag. So, what the @#$% are they talking about? :-). (From: Asimov (email@example.com)). 'Dag' is short for Aquadag. It is a type of paint made of a graphite pigment which is conductive. It is painted onto the inside and outside of picture tubes to form the 2 plates of a high voltage filter capacitor using the glass in between as dielectric. This capacitor is between .005uF and .01uF in value. This seems like very little capacity but it can store a substantial charge with 25,000 volts applied. The outside "dag" is always connected to the circuit chassis ground via a series of springs, clips, and wires around the picture tube. The high voltage or "Ultor" terminal must be discharged to chassis ground before working on the circuit especially with older TV's which didn't use a voltage divider to derive the focus potential or newer TV's with a defective open divider. For more details, see the document: "TV and Monitor CRT (Picture Tube) Information.
When powering up a monitor (or any other modern electronic devices with expensive power semiconductors) that has had work done on any power circuits, it is desirable to minimize the chance of blowing your newly installed parts should there still be a fault. There are two ways of doing this: use of a Variac to bring up the AC line voltage gradually and the use of a series load to limit current to power semiconductors. Actually using a series load - a light bulb is just a readily available cheap load - is better than a Variac (well both might be better still) since it will limit current to (hopefully) non-destructive levels. What you want to do is limit current to the critical parts - usually the horizontal output transistor (HOT). Most of the time you will get away with putting it in series with the AC line. However, sometimes, putting a light bulb directly in the B+ circuit will provide better protection as it will limit the current out of the main filter capacitors to the HOT. Actually, an actual power resistor is probably better as its resistance is constant as opposed to a light bulb which will vary by 1:10 from cold to hot. The light bulb, however, provides a nice visual indication of the current drawn by the circuit under test. For example: * Full brightness: short circuit or extremely heavy load - a fault probably is still present. * Initially bright but then settles at reduced brightness: filter capacitors charge, then lower current to rest of circuit. This is what is expected when the equipment is operating normally. There could still be a problem with the power circuits but it will probably not result in an immediate catastrophic failure. * Pulsating: power supply is trying to come up but shutting down due to overcurrent or overvoltage condition. This could be due to a continuing fault or the light bulb may be too small for the equipment. Note: for a TV or monitor, it may be necessary (and desirable) to unplug the degauss coil as this represents a heavy initial load which may prevent the unit from starting up with the light bulb in the circuit. The following are suggested starting wattages: * 40 W bulb for VCR or laptop computer switching power supplies. * 100 W bulb for small (i.e., B/W or 13 inch color) monitors or TVs. * 150-200 W bulb for large color monitors or projection TVs. A 50/100/150 W (or similar) 3-way bulb in an appropriate socket comes in handy for this but mark the switch so that you know which setting is which! Depending on the power rating of the equipment, these wattages may need to be increased. I have had to go to a 300 W light bulb for some computer monitors. However, start low. If the bulb lights at full brightness, you know there is still a major fault. If it flickers or the TV (or other device) does not quite come fully up, then it should be safe to go to a larger bulb. Resist the temptation to immediately remove the bulb at this point - I have been screwed by doing this. Try a larger one first. The behavior should improve. If it does not, there is still a fault present. Note that some TVs and monitors simply will not power up at all with any kind of series load - at least not with one small enough (in terms of wattage) to provide any real protection. The microcontroller apparently senses the drop in voltage and shuts the unit down or continuously cycles power. Fortunately, these seem to be the exceptions.
You will void the warranty - at least in principle. There are usually no warranty seals on a monitor so unless you cause visible damage or mangle the screws or plastic, it is unlikely that this would be detected. You need to decide. A monitor still under warranty should probably be returned for warranty service for any covered problems except those with the most obvious and easy solutions. Another advantage of using warranty service is that should your problem actually be covered by a design change, this will be performed free of charge. And, you cannot generally fix a problem which is due to poor design! Getting into a monitor is usually quite simple requiring the removal of 2-10 Philips or 1/4" hex head screws - most around the edge of the cabinet or underneath, a couple perhaps in the rear. Disconnect the input and power cables first as it they stay with catch on the rear cover you are detaching. Reconnect whatever is needed for testing after the cover is removed. Set the screws aside and make notes if they are not all of the same length and thread type - putting a too long screw in the wrong place can short out a circuit board or break something else, for example. A screw that is too short may not be secure. Once all visible screws are out, try to remove the cover. There still may be hidden catches or snaps around the edges or seam or hidden beneath little plastic or rubber cosmetic covers. Sometimes, the tilt-swivel base will need to be removed first. If no snaps or catches are in evidence, the cover may just need a bit of persuasion in the form of a carefully placed screwdriver blade (but be careful not to damage the soft plastic). A 'splitting' tool is actually sold for this purpose. As you pull the cover straight back (usually) and off, make sure that no other wires are still attached. Often, the main circuit board rests on the bottom of the cover in some slots. Go slow as this circuit board may try to come along with the back. Once the back is off, you may need to prop the circuit board up with a block of wood to prevent stress damage and contact with the work surface. Most - but not all - monitors can be safely and stably positioned either still on the tilt-swivel base or on the bottom of the frame. However, some will require care as the circuit board will be vulnerable. Larger monitors are quite heavy and bulky. Get someone to help and take precautions if yours is one of the unstable variety. If need be, the monitor can usually safely be positioned on the CRT face if it is supported by foam or a folded blanket. Once the cover is off, you will find anywhere from none to a frustratingly large number of sheetmetal (perforated or solid) shields. Depending on which circuit boards need to be accessed, one or more of these shields may need to be removed. Make notes of which screws go where and store in a safe place. However, manufacturers often place holes at strategic locations in order to access adjustments - check for these before going to a lot of unnecessary bother. Note: sheetmetal usually has sharp edges. Take care. Reassemble in reverse order. Getting the circuit board to slide smoothly into its slots may take a couple of attempts but otherwise there should be no surprises.
Both electrical and mechanical dangers lurk: * Main filter capacitor(s). This is the most dangerous (not the HV as you would expect). Fortunately, these capacitors will normally discharge in a few minutes or less especially if the unit is basically working as the load will normally discharge the capacitors nearly fully as power is turned off. With TVs, the main filter capacitor is nearly always on the mainboard. Monitors are more likely to have a separate power supply module. However, you should check across this capacitor - usually only one and by far the largest in the unit - with a voltmeter and discharge as suggested in the section: "Safe discharging of capacitors in TVs and video monitors" if it holds more than a few volts (or wait longer) before touching anything. Some of these are as large as 1,000 uF charged to 160 V - about 13 w-s or a similar amount of energy as that stored in an electronic flash. This is enough to be potentially lethal under the wrong circumstances. * High Voltage capacitor formed by the envelope of the CRT. It is connected to the flyback transformer by the fat (usually red) wire at the suction cup (well, it looks like one anyhow) attached to the CRT. This capacitor can hold a charge for quite a while - weeks in the case of an old tube type TV! If you want to be doubly sure, discharge this also. However, unless you are going to be removing the HV connector/flyback, it should not bother you. The energy stored is about 1 w-s but if you touch it or come near to an exposed terminal, due to the high voltage, you will likely be handed *all* the energy and you *will* feel it. The danger is probably more in the collateral damage when you jump ripping flesh and smashing your head against the ceiling. Some people calibrate their jump based on voltage - about 1 inch/V. :-). There will be some HV on the back of the circuit board on the neck of the CRT but although you might receive a tingle but accidentally touching the focus or screen (G2) pins, it is not likely to be dangerous. * CRT implosion risk. Don't hammer on it. However, it is more likely that you will break the neck off the tube since the neck is relatively weak. This will ruin your whole day and the TV or monitor but will likely not result in flying glass everywhere. Just, don't go out of your way to find out. * Sharp sheet metal and so forth. This is not in itself dangerous but a reflex reaction can send your flesh into it with nasty consequences.
The first thing you will notice when you remove the cover is how super dusty everything is. Complements to the maid. You never dreamed there was that much dust, dirt, and grime, in the entire house or office building! Use a soft brush (like a new paintbrush) and a vacuum cleaner to carefully remove the built up dust. Blowing off the dust will likely not hurt the unit unless it gets redeposited inside various controls or switches but will be bad for your lungs - and will spread dirt all over the room. Don't turn anything - many critical adjustments masquerade as screws that just beg to be tightened. Resist the impulse for being neat and tidy until you know exactly what you are doing. Be especially careful around the components on the neck of the CRT - picture tube - as some of these are easily shifted in position and control the most dreaded of adjustments - for color purity and convergence. In particular, there will be a series of adjustable ring magnets. It is a good idea to mark their position in any case with some white paint, 'white out', or a Magic Marker so that if they do get moved - or you move them deliberately, you will know where you started.
There are times when it is desirable to remove the chassis or mainboard and work on it in a convenient location without having to worry about the attachments to the CRT and cabinet circuitry. My approach is usually to do as much work as possible without removing the main board and not attempt to power it up when disconnected since there are too many unknowns. Professionals will plug the chassis into a piece of equipment which will simulate the critical functions but this is rarely an option for the doit-yourselfer. Note that if you have a failure of the power supply - blown fuse, startup, etc., then it should be fine to disconnect the CRT since these problems are usually totally unrelated. Tests should be valid. However, if you really want to do live testing with the main board removed, here are some considerations. There are usually several connections to the CRT and cabinet: * Deflection yoke - since the horizontal coils are part of the horizontal flyback circuit, there could be problems running without a yoke. This could be anything from it appearing totally dead to an overheating or blown horizontal output transistor. There may be no problems. Vertical and any convergence coils may or may not be problems as well. * CRT video Driver board - pulling this should not usually affect anything except possibly video output and bias voltages. * CRT 2nd anode - without the CRT, there will be no capacitor to filter the high voltage and you would certaily want to insulate the HV connector **real** well. I do not know whether there are cases where damage to flyback could result from running in thie manner, however. * Front panel controls - disconnecting these may result in inability to even turn the unit on, erratic operation, and other unexpected behavior. * Degauss - you just won't have this function when disconnected. But who cares - you are not going to be looking at the screen anyhow. * Remote sensor - no remote control but I doubt that the floating signals will cause problems. * Speakers - there will be no audio but this should not cause damage. If you do disconnect everything, make sure to label any connectors whose location or orientation may be ambiguous. Most of the time, these will only fit one way but not always.
For general viewing, subdued lighting is preferred. Avoid backlighting and direct overhead lighting if possible. Display an image with a variety of colors and the full range of brightness from deep shadows to strong highlights. For PCs, a Windows desktop is generally satisfactory. An outdoor scene on a sunny day is excellent for studio monitors. Alternatively, use a test pattern specially designed for this purpose. Turn the BRIGHTNESS and CONTRAST controls (or use the buttons) all the way down. Increase the BRIGHTNESS until a raster is just visible in the darkest (shadow) areas of the picture. Increase the CONTRAST until the desired intensity of highlights is obtained. Since BRIGHTNESS and CONTRAST are not always independent, go back and forth until you get the best picture. On monitors with a color balance adjustment, you may want to set this but unless you are doing photorealistic work, using the manufacturer's defaults will be fine unless you need to match the characteristics of multiple monitors located side-by-side.
One of the most common complaints is that the monitor is not as crisp as it used to be - or just not as sharp as expected. Assuming that the focus has just been gradually getting worse over time, tweaking the internal focus control may be all that is needed. Some monitors have the focus adjustment accessible through a (possibly unmarked) hole in the side or rear of the case. If there is a single hole, it is almost certainly for overall focus. If there are two holes, one may be the screen (G2 - master brightness) or the two adjustments may be for different aspects of focus (e.g., horizontal and vertical). Just carefully observe what happens when each adjustment is moved a little so that you can return it to its original setting if you turned the wrong one. Use a thin insulated screwdriver - preferably with a plastic blade. As a extra precaution, determine of the screwdriver will mate easily with the adjustment with the monitor **off** (don't turn anything, however). Where there are two adjustment knobs on the flyback transformer, the top one is generally for focus and the bottom one is for G2. Most inexpensive monitors have only what is known as static focus - a constant voltage derived from the HV power supply is applied to the focus grid of the CRT. This does not allow for optimal focus across the screen and any setting is just a compromise between central and edge sharpness. Better monitors will have (in addition) H and V focus controls. These are for dynamic focus adjustments. There may be some interaction between the static and dynamic adjustments. If either of these controls has no effect or insufficient range, then there may be a fault in the circuitry for that particular adjustment - a fault with the driver, waveform source, power supply, etc. The most sophisticated schemes use a microprocessor (or at least digital logic) to specify the waveform for each section of the screen with a map of correction values stored in non-volatile memory. It would be virtually impossible to troubleshoot these systems without detailed service information and an oscilloscope - and even then you might need a custom adapter cable and PC software to adjust values! Also see the section: "About the quality of monitor focus". If you need to go inside to tweak focus pots: Safety: as long as you do not go near anything else inside the monitor while it is on AND keep one hand in you pocket, you should be able to do this without a shocking experience. Plug it in, turn it on and let it warm up for a half hour or so. Set your PC (or other video source) to display in the resolution you use most often. First turn the user brightness and contrast fully counterclockwise. Turn brightness up until the raster lines in a totally black area appear, then back a hair until they disappear. Then, turn the contrast control up until you get a fairly bright picture. Fullly clockwise is probably ok. Adjust FOCUS for generally best focus. You will not be able to get it razor sharp all over the screen - start at the center and then try to get the edges and corners as good as you can without messing up the center too much. Double check that the focus is ok at your normal settings of brightness and contrast and at other resolutions that you normally use. The focus pot is usually located on the flyback transformer or on an auxiliary panel nearby. The focus wire usually comes from the flyback or the general area or from a terminal on a voltage the multiplier module (if used). It is usually a wire by itself going to the little board on the neck of the CRT. The SCREEN control adjusts background brightness. If the two controls are not marked, you will not do any damage by turning the wrong one - it will be immediately obvious as the brightness will change rather than focus and you can then return it to its original position (or refer to the section on brightness adjustments to optimize its setting). On a decent monitor, you should be able to make out the individual scanning lines at all resolutions though it will be toughest at the highest scan rates. If they lines are fuzzy, especially in bright areas, then focus may need to be adjusted or there may be an actual fault in the focus circuitry or a defective or just marginal CRT.
A monitor which has a picture that is very dark and cannot be adequately set with the user brightness and contrast controls may need internal adjustment of the SCREEN (the term, screen, here refers to a particular electrode inside the CRT, not really the brightness of the screen you see, though it applies here), MASTER BRIGHTNESS, or BACKGROUND level controls. As components age, including the CRT, the brightness will change, usually decrease. The following procedure will not rejuvenate an old CRT but may get just enough brightness back to provide useful functionality for a few months or longer. If the problem is not with the age of the CRT, then it may return the monitor to full brightness. The assumption here is that there is a picture but the dark areas are totally black and the light areas are not bright enough even with the user brightness control turned all the way up. Note that circuit problems can also cause similar symptoms. These are particularly likely if the brightness descresed suddenly - CRT emission problems will result in a gradual decrease in brightness over time. In most cases, the cover will need to be removed. The controls we are looking for may be located in various places. Rarely, there will be access holes on the back or side. However, if there are unmarked holes, then the FOCUS and SCREEN controls are the most likely possibilities. The controls may be located on the: * Flyback (LOPT) transformer. Usually there is a master screen control along with a focus control on the flyback transformer. * A little board on the neck of the CRT. There may be a master screen control. a master brightness control, a master background level control, or individual controls for red, green, and blue background level. Other variations are possible. There may also be individual gain/contrast controls. * Main video board is less common, but the background level controls may be located here. Display a picture at the video resolution you consider most important which includes both totally black and full white areas which also includes sharp vertical edges. Set the user brightness control to its midpoint and the user contrast control as low as it will go - counterclockwise. Let the monitor warm up for at least 15 minutes so that components can stabilize. If there is a MASTER BRIGHTNESS or BACKGROUND level control, use this to make the black areas of the picture just barely disappear. Them, increase it until the raster lines just appear. (They should be a neutral gray. If there is a color tint, then the individual color background controls will need to be adjusted to obtain a neutral gray.) If there is no such control, use the master screen control on the flyback. If it is unmarked, then try both of the controls on the flyback - one will be the screen control and the other will be focus - the effects will be obvious. If you did touch focus, set it for best overall focus and then get back to the section on focus once you are done here. If there are individual controls for each color, you may use these but be careful as you will be effecting the color balance. Adjust so that the raster lines in a black area are just visible and dark neutral gray. If there is a 'service switch' you may prefer to make the adjustment with this in the service position. The raster will collapse to a single horizontal line and the video input will be disabled and forced to black. The BACKGROUND or SCREEN control can then be adjusted as above. Now for the gain controls. On the little board on the neck of the CRT or on the video or main board there will be controls for R, G, and B DRIVE (also may be called GAIN, or CONTRAST - they are the same). The knobs or slots may even be color coded as to which primary (R,G,B) it affects. If there are only two then the third color is fixed and if the color balance in the highlights of the picture was ok, then there is nothing more you can do here. Set the user contrast control as high as it will go - clockwise. Now adjust each internal color DRIVE control as high as you can without that particular color 'blooming' at very bright vertical edges. Blooming means that the focus deteriorates for that color and you get a big blotch of color trailing off to the right of the edge. You may need to go back and forth among the 3 DRIVE controls since the color that blooms first will limit the amount that you can increase the contrast settings. Set them so that you get the brightest neutral whites possible without any single color blooming. Note that this is ignoring the effects of any beam current or brightness limiter circuitry. Any recommendations in the service manual should be followed to minimize the chance of excess X-ray emissions as well as to avoid burn-in of the phosphor screen. Now check out the range of the user controls and adjust the appropriate internal controls where necessary. You may need to touch up the background levels or other settings. Check at the other resolutions and refresh rates that you normally use. If none of this provides acceptable brightness, then either your CRT is in its twilight years or there is something actually broken in the monitor. If the decrease in brightness has been a gradual process over the course of years, then it is most likely the CRT. As a last resort you can try increasing the filament current to the CRT the way CRT boosters that used to be sold for TVs worked. See the section: "Brightening an old CRT".Go to [Next] segment
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