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There are several symptoms that are basically similar: * Blooming is defined as an expansion of the raster or horizontal sections of the raster with bright material. For example, switching between dark and light picture causes the size of the picture to expand by 10%. A slight change in size is unavoidable but if it is greater than 1 or 2 percent from a totally black image to a full white one, this is either an indication of a defective TV or one that is badly designed. The cause is poor low or high voltage regulation. Check the B+ to the horizontal deflection. This is usually well regulated. If it is varying in sympathy to the size changes, trace back to determine why the low voltage regulator is not doing its job. The reason for the size change is that the high voltage is dropping and reducing the stiffness of the electron beam. * Expansion of the raster width in areas of bright imagery is an indication of short term regulation problems. The video drive may be interacting with the other power supplies. Check for ripple - this would be at the vertical scan rate - in the various regulated power supplies. The cause may be a dried up electrolytic capacitor - once you locate the offending voltage, test or substitute capacitors in that supply. In both these cases, if this just started after some work was done to the TV, the brightness limiter and/or video drive may simply be set so high that the TV cannot supply enough current to the high voltage. If the brightness is acceptable with these turned down slightly and still have acceptable brightness, then there may be nothing wrong. * Breathing is defined as a periodic change in the size of the raster which may be independent of what is displayed or its severity or frequency may be related to the brightness or darkness of the image. This is another type of regulation problem and may be caused by bad electrolytic capacitors or other components in the low voltage power supplies. If the TV uses a switchmode power supply or low voltage regulator separate from the horizontal deflection, first check its output(s) for a variation in voltage at the breathing rate. Test with a light bulb or resistor load to confirm that the problem is here and not the deflection or other subsystem of the TV. * A condition with somewhat similar symptoms is bad focus - fuzzy picture - but only with bright (high beam current) scenes. This could be just a matter of adjusting the focus control but may also indicate sub-optimal filament voltage due to bad connections or components in the filament circuit, or a tired worn CRT. You won't get high beam current without some serious spot blooming (a fat beam because too much cathode area is used) and you will get cathode 'poisoning' after prolonged use. Visually inspect the neck of the CRT for the normal orange glow of the filaments and check for bad connections and bad parts.
Symptoms may include fluctuating focus or brightness. In extreme cases, the result may be a too bright or dark picture or other behavior caused by breakdown in the Focus/Screen(G2) divider network. Usually, this will require flyback replacement to repair reliably. Sometimes, the section with the controls can be snapped apart and cleaned but this is not common. First, just try rotating the screen (G2) control back and forth a few times. This may clean up the contacts and eliminate the erratic behavior. Possibly, positioning it a bit to one side of the original location will help. Then, use the individual or other master background/bias adjustments to compensate for the improper brightness. If this doesn't help, here is a 'well it's going in the dumpster anyhow' procedure to try: After discharging the CRT (so you don't get zapped) drill a tiny hole in the plastic cover near the bad control. Be careful you don't damage anything inside - you just want access to the contacts of the controls. Use a hand drill with, say, a 1/16" bit. Don't drill more than about 1/8" deep which should enter the airspace. Then spray some contact cleaner through the hole and work the controls. Wait sufficient time for the everything to dry COMPLETELY and see if behavior changes (or it works at all). This is a 'you have got to be kidding' type of repair so no guarantees :-). If by some miracle it does work, fill the hole with a drop of RTV or just put a couple of layers of electrical tape over it.
This is kludge number 41256 but may be the difference between a bit more life and the dumpster. If the previous extreme measures don't help, then it may be possible to simply substitute a good divider network externally. Note that if there is evidence of internal breakdown in the divider of the original flyback (hissing, cracks, overheating, bulging case, etc.), this will not work unless you can disconnect it from its HV connection. There are two issues: 1. Is this a stable situation? Even if you provide an external substitute, the parts inside the flyback may continue to deteriorate eventually resulting in other more total failure of the flyback or worse. 2. If you provide an external focus/screen divider, it must be done is such a manner (including proper mounting and super insulation) such that it cannot be called into question should there be a fire where the monitor is even the slightest bit suspect. Various size external focus/screen divider networks can be purchased but whether this is truly a cost effective solution is not obvious. (From: Larry Sabo (sabo@storm.ca)). I just ordered a 'bleeder resistor' from Data Display Ltd (Canadian sub of CCS) to use as a cure for flybacks with flaky focus/screen pots. It contains focus and screen pots, and costs Cdn$ 16.99, which is a lot less than a complete flyback, that's for sure. I expect it will be compatible with quite a wide range of flybacks. I have used bleeder resistor assemblies from duff flybacks a couple of times with good success. You connect the HV lead into the HV cap of the original flyback, ground all pins of the sub flyback, and use the focus and screen leads from the sub bleeder assembly in place of the originals. Looks like hell but works fine. Mounting (and securing) the substitute is a challenge given the limited space available. I only use this approach on what would otherwise be uneconomical to repair, and always advise the owner or customer of the cobbling job. It also enables you to verify whether it is the flyback that needs replacement, versus the CRT.
The following applies to both CRT focus voltage (which should be a few KV) and screen or G2 voltage (which should be several hundred V). "The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal." This is very likely a short between electrodes inside the CRT unless there is something on the neck board that is breaking down as a result of some connection to the CRT. The flyback should largely not know the difference with the socket plugged into the CRT. One possibility is that glue used to hold components down on some circuit boards has deteriorated and turned conductive. Check for tan to brown stuff shorting traces on the CRT neck board. If this is present on the focus or screen traces or wires, it may just be your problem. Scrape off all of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would result in all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts, a couple microfarads) between G2 and G1 or focus, you **will** know if tapping the neck results in a momentary short! I cannot predict whether this will be a temporary cure or permanent killer. See the section: "Rescuing a shorted CRT". Here is another thing to try: put a 100 M ohm or so resistor between SCREEN and the CRT socket. This should not affect the behavior much until the failure occurs. Then, check the voltage on both sides with a high impedance voltmeter (1000 M). If the CRT is arcing, it will be much lower on the CRT side and will probably fluctuate. You can play similar games with focus voltage.
In some cases, the focus wire - the not-so-fat wire from the flyback or focus divider - may terminate directly in the CRT socket with no obvious means of freeing it should flyback replacement be needed. One alternative is simply to cut the wire in a location that is well away from any place to short out, solder, and then do a most excellent job of insulating the splice. However, you may find that the cap on the CRT socket snaps off using a thin knife blade or screwdriver. The wire may be soldered or just pressed in place in such a way that pulling it out is difficult or impossible without removing the cover. (From: Raymond Carlsen (rrcc@u.washington.edu)). The last one I worked on puzzled me for a few moments. See if you can see a space between the little cup (where the wire enters the socket) and the socket itself. Pry up on the cap with a knife and it should pop right off. The wire is soldered to a pin under it. Don't apply heat for very long... you may melt the socket.
"I have a 3-5 yr old TV that loses screen voltage. I believe that the problem is specific to the CRT or the flyback, either one is a guess I'd rather be sure of prior to ordering a part. The screen voltage will come up to normal after sitting over night, 400 V or so. After approximately 5 minutes or slightly longer, I hear a slight arcing. From that point on, the screen voltage will wander anywhere from 75 V up to maybe 150 V. Adjustment of the screen control on the flyback has only a small effect and is not permanent. Removing the CRT pcb results in the screen voltage returning to normal. I cannot find the source of the arcing, as it happens quickly and I have always been on the other side of the set when it happens. I have replaced the crt socket, thinking the spark gap was arcing. I have checked the CRT for G1 and HK shorts on a sencore crt checker, it checks good, but I am aware that since it is an intermittent problem, that the checker probably will not catch it." This sounds like a CRT short unless there is something on the neck board that is breaking down. The Sencore may not provide the same high voltages as normal screen (several hundred volts) or focus (several thousand volts). The flyback should largely not know the difference whether the screen or focus electrode of the CRT is connected or not. The current should be neglegible. One possibility is that glue used to hold components down on some circuit boards has deteriorated and turned conductive. Check for tan to brown stuff shorting traces on the CRT neck board. If this is present on the focus or screen traces or wires, it may just be your problem. Scrape off all of the old glue and then clean thoroughly. Repair any damaged traces. What happens to the HV? A HV breakdown possibly inside the CRT would result in all the voltages being dragged down. What happens to the picture? If you connect a charged HV capacitor (guessing a couple hundred volts, a couple microfarads) between G2 and G1 or focus, you **will** know if tapping the neck results in a momentary short! I cannot predict whether this will be a temporary cure or permanent killer. Here is another thing to try: put a 100 M ohm or so resistor between SCREEN (or FOCUS) and the CRT socket. This should not affect the behavior much until the failure occurs. Then, check the voltage on both sides with a high impedance voltmeter (>1000 M). If the CRT is arcing, it will be much lower on the CRT side.
This means absolutely no color - equivalent to a black and white picture. Not even a hint of color. First, confirm that the source is actually in color - try another channel or input device. Next, check the settings of the color control - it may have accidentally been turned down. If your TV has some kind of automatic picture mode, try turning if off and adjusting the color control. Try adjusting fine tuning if you have such a control and the problem is with a broadcast or cable transmission. At this point with a confirmed color signal source, there is a problem with the chroma circuitry. Note that to the average person, the obvious question becomes: is my color picture tube bad? The answer is a definitive NO. It is virtually impossible for a defective CRT to cause a total loss of color. A defective CRT can cause a lack of a primary color - R, G, or, B or a short between two colors which will mess up the color but is not likely to result in a black and white picture. Some possibilities in no particular order: 1. Weak signal or defect in tuner/IF causing loss of signal strength. 2. Coler killer set too high (internal control) if it has one. 3. Defective part around the chroma chip/circuit. Faulty color oscillator. 4. Bad connections in area of chroma chip/circuit. 5. Defective chroma chip (don't suspect this first just because it is probably very expensive). A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. Try prodding the main board around the chroma chip with an insulated tool to see if you can make the color come and go. I had one set where a $.02 resistor decided to open up causing just this problem - perfect BW picture, no color. Another had a coil with a broken wire.
This means you have lost the luminance input to the chroma decoder or final video chip. A failure of the brightness limiter may result in similar symptoms. A few common causes are: * Check the service switch (if any). Its contacts may be dirty and moving it back and forth a few times or using contact cleaner may be all that is needed. * Check for open high value resistors around the chroma decoder IC. * Check for open high value resistors in the brightness limiter circuit. With a scope and schematic (or even just a pinout for the chip), you should be able to trace the luminance signal to see where it is getting lost. This is also *not* a picture tube problme :-).
The following assumes that the picture is fine but the brightness is fixed - probably at too high a level. However, there could be several interrelated problems if a common supply voltage were missing, for example. If it is a knob, then it should be varying the control grid (G1) voltages relative to the cathodes (K) of the CRT. This is not likely to be a very complex circuit. If you do not have a schematic, I would start by tracing from the control, check continuity and solder connections. Check the control itself for proper operation with an ohmmeter. A power supply going to one side of the control (negative probably) may be missing. Tbe control grid voltage will end up on the little board on the neck of the CRT - check there as well for bad solder connections or open resistors. If brightness is a digital control, then you will need a schematic unless there is an obvious bad connection.
If the problem is slight and/or has gradually gotten worse, this may just require an adjustment of the color brightness/background/bias and/or color gain/drive controls inside the TV. See the section: "Color balance adjustment". Note that if it is possible to obtain a good black and white picture with the user color control set to its minimum, then this is not likely a problem with one of the primary color channels (red, green, or blue) but with the chroma decoding circuitry. Or, perhaps, you are just watching MTV! Even if it appears as though there is an excess, this may actually be a reduction in one of the primary colors. For example, a magenta tinge is represents a reduction in the strength of the green signal. * Too high an intensity for one of the color channels will result in a tint of one of the primaries: red, green or blue. * Too low an intensity for one of the color channels will result in a tint of the complement of one of the primaries: yellow, cyan, or magenta. * Problems mainly in the shadows or dark areas of the picture usually represent a fault with brightness/bias/background. * Problems mainly in the highlights or bright areas of the picture usually represent a fault with the gain/drive. A color that that is now suddenly brighter or darker than normal resulting in incorrect color balance or a tint in the background could be due to a number of causes: * Bad connections or bad component in video amplifier or on CRT neck board for that color. * Fault in chroma decoder. * Weak gun in CRT (reduced color).
The means colors that are not normal and that adjustment of the user controls is not able to correct it so that all colors of the picture are properly displayed at the same time. For example, you are unable to get any yellows or blues in scenes that should have these colors.. Make sure the user color and tint controls have not been accidentally turned while cleaning or purposedly misadjusted by small (or large) kids. Perform the user setup described in the section: "User picture adjustment". Confirm that the source is not a weird color video - try another channel or a tape. Verify that this is not a missing color problem - one of the primary R, G, or B, has disappeared. If so, refer to the section: "Intermittent or missing colors". Once these have been eliminated, you are left with the following possibilities: 1. Defective part around the chroma chip/circuit. Misadjusted color oscillator. 2. Bad connections or short circuit in area of chroma chip/circuit. 3. Defective chroma chip (don't suspect this first just because it is probably very expensive). 4. Bad degauss circuit resulting in lack of degauss or abrupt termination of degauss current rather than smooth tail off. The CRT is not being properly demagnetized and color purity is totally messed up. 5. Bad CRT - the shadow mask has been damaged and it is impossible to properly adjust purity across the screen. A service manual or Sams', DMM, & scope will help greatly in attempting to troubleshoot this unless it is an obvious bad connection. For (1)-(3), try prodding the main board around the chroma chip with an insulated tool to see if you can restore normal color. For (4) try manually degaussing (see the section: "Degaussing (demagnetizing) a CRT". If this clears up the colors until at least when it is power cycled, then a degauss problem is likely. Something as simple as a bad resistor or inductor can be the cause - don't immediately suspect the most expensive and difficult to replace part.
Remove the picture tube socket (carefully!) and clean the pins with fine sandpaper and use contact cleaner on the socket. This source of bad connections can result in a variety of erratic symptoms.
Any intermittent problems with monitors that cause random sudden changes in the picture brightness, color, size, or position are often a result of bad connections. Bad solder joints are very common in TVs and monitors due both to poor quality manufacturing as well as to deterioration of the solder bond after numerous thermal cycles and components running at high temperature. Without knowing anything about the circuitry, it is usually possible to cure these problems by locating all bad solder connections and cleaning and reseating internal connectors. The term 'cold solder joint' strictly refers to a solder connection that was either not heated enough during manufacturing, was cooled too quickly, or where part pins were moved before the solder had a chance to solidify. A similar situation can develop over time with thermal cycling where parts are not properly fastened and are essentially being held in by the solder alone. Both situations are most common with the pins of large components like transformers, power transistors and power resistors, and large connectors. The pins of the components have a large thermal mass and may not get hot enough during manufacturing. Also, they are relatively massive and may flex the connection due to vibration or thermal expansion and contraction. To locate cold solder joints, use a strong light and magnifier and examine the pins of large components for hairline cracks in the solder around the pin. Gently wiggle the component if possible (with the power off). Any detectable movement at the joint indicates a problem. With the power on, gently prod the circuit board and suspect components with an insulated tool to see if the problem can be effected. When in doubt, resolder any suspicious connections. Some monitors may use double sided circuit boards which do not have plated through holes. In these cases, solder both top and bottom to be sure that the connections are solid. Use a large enough soldering iron to assure that your solder connection is solid. Put a bit of new solder with flux on every connection you touch up even if there was plenty of solder there before.
I can think of several potential reasons - all solvable but at higher manufacturing cost. 1. Mass of large component leads (like shields) does not get adequately heated during manufacture leading to latent cold solder joints. While they may look ok, the solder never actually 'wetted' the heavy pins and therefore did not form a good mechanical or electrical bond. 2. Thermal cycles and differential thermal coefficients of circuit boards, traces, and solder. While it is not easy to do anything about the material properties, using plated through-holes or a similar mechanical via would greatly increase the surface area of the joint and prevent the formation of cracks. 3. Vibration. This is also directly related to the single sided circuit boards without plated through-holes to strengthen the joints. 4. Lack of adquate mechanical support (single sided circuit boards without plated through-holes (vias). I believe that the single most significantimprovement would come about by using plated trhough-holes but this would add to the cost and apparently the consumer is not willing to pay more for better quality and reliability! Some designs have used rivlets - mechanical vias instead of plated ones. While this is good in principle, the execution has often been flawed where cold solder joints resulted between the rivlets and the circuit board traces due to lack of adequate process control. The Sony and RCA/GE tuner shield problem is interesting because this could have been solved years ago at essentially no additional cost as other manufacturers - and their own repair procedures - have proven.
This is a catch-all for some of the most common TV and monitor problems.
* If gently whacking the set can make the color(s) come and go suddenly, then
bad connections are probable. The most likely place for these are solder
pads on the little circuit board on the neck of the CRT or even dirty CRT
socket pins that are not making solid contact. Try prodding the CRT neck
board with an insulated stick to see if you can affect the colors.
Although not impossible, this is not likely to be a CRT problem.
* If the color fades in and out with a delay of about 10-15 seconds, it is
probably intermittent power to the CRT filament for that color and probably
means a bad CRT since the three filaments are wired in parallel inside the
CRT. One of the internal connections has come loose.
Look in the neck of the CRT to make sure all three filaments are glowing
orange. If one is out or goes on and off, toss the set. Replacing the CRT
is probably not worth it. However, if they all go on and off together (all
colors would be fading in and out though perhaps not quite in unison), then
bad connections for the CRT filaments on the CRT neck board are indicated.
To narrow down the problem:
* Locate the output for the bad color on the video driver board on the
neck of the CRT. This will probably read a significantly higher
voltage than the corresponding pins for the good colors. A circuit
problem is likely - probably on this board.
* Test components on this board for the good and bad color channels. A
shorted transistor or open resistor can kill one channel. Swap parts
between good and bad colors to confirm.
* Gently pull the CRT neck board off of the CRT and replace it. This will
tend to clean the contacts.
* Connect an output of the video/chroma circuit/chip that is working (i.e.,
a color that appears on the screen) to *all* three color drivers on the CRT
neck board.
- If you now get a more-or-less black and white picture (there may be a
moderate color tint as the relative intensities of R,G,B may not be
balanced), the problem is likely with the chroma decoder or its support
circuitry.
Note: the picture will be the intensity of only one color channel so it
will not be quite *normal* in any case.
- If you still have missing or messed up colors, the problem is on the CRT
neck board or with the CRT.
Most of the causes of intermittent colors boil down to bad connections
of one form or another. For totally dead colors - not intermittent - bad
components are also a possibility.
* Printed circuit board on the CRT neck. This is a common location for
cold solder joints. Check with a bright light and magnifying glass
for hairline cracks around the pins of larger parts. Prod and tap with
an insulated tool to see if the problem is effected. Resolder if necessary.
* Cold solder joints elsewhere in TV or monitor usually around the pins of
large parts such as transformers, power transistors and resistors, and
internal connectors.
* Internal connectors (including CRT socket) that need to be cleaned and
reseated. Remove, clean with contact cleaner, burnish, and replace.
Anytime that intermittent symptoms are experienced, I recommend gently whacking the patient to determine if mechanical shock or vibration affects the behavior. Here are a couple of responses to this suggestion. (The following is from Marc Gelfond (71363.1700@CompuServe.COM)): I just love the bit about "whacking it". It brings to mind an episode from the old Andy Griffith show, where a new fangled piece of electronics gear, was broght into Emmets repair shop. After many long hours of fruitless troubleshooting, out of frustration Emmet gave the thing a whack, and sure enough it fixed the problem. As we say in the Telephony business, it "CCWT" or Came Clear While Testing.Another saying is that it "CCBFM" Came Clear By F------ Magic!! (To which Gavin Adams (gaa@hopi.com) comments): In the video industry we had a saying concerning malfunctioning gear: "If it's broke, hit it with a hammer" "If that doesn't fix it, paint it and sell it" My DEC 16" monitor is case in point. Evey once in a while it would lose sync, and smacking it would bring it back (sometimes a few smacks). Recently it gave up the ghost completely, and after the local DEC office gave me a quote of $900 to fix it (Bermuda), I ordered a new Viewsonic 17" for the same price. I ripped the guts out of the DEC beast, painted it with a marble finish, put plants in it, and sold it! :>
During the time the electron beam is returning from right to left at the end of a line and bottom to top (over the course of multiple lines), it is supposed to be result in no visible light on the screen. However, a number of faults can result in visible retrace lines. The appearance will likely be a general reduction in contrast from the visible horizontal retrace on every scan line and two dozen or so diagonal lines lines (lower left to upper right) resulting from the vertical retrace. The retrace lines may be either white or gray (possibly with a slight color tint due to unequal settings of the color adjustments) or a primary color - red, green, or blue. Anything in between is also possible but less likely.
Where all colors are involved - the lines are essentially white or gray (or with a slight tint due to slight unequal settings of the color adjustments), look for something common like an incorrectly adjusted screen (G2) or master brightness/background/bias control or a problem in one of these circuits, a defective power supply or a problem in the blanking circuitry: * Screen (G2) or master brightness/background/bias control - mark setting and then see if a slight adjustment removes the retrace lines. See the chapter: "TV Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Power supply or connection to CRT neck board - insufficient voltage will result in the CRT never totally blanking. Check (usually scan derived) power supply components (from flyback). * General power supply - check B+ for correct value and ripple. A main power supply fault might result in these symptoms (and usually many others). * Blanking circuit - this may be a part of the video/chroma chip or separate. Check waveforms to determine if the blanking pulses are making it to the video output.
Where only one color is showing, suspect an incorrectly adjusted individual background/bias control or bad part on the CRT neck board for that color. * Individual brightness/background/bias control(s) - mark setting of pot for the problem color and then see if a slight adjustment removes the retrace lines. See the chapter: "TV Adjustments". Of course, if this happened suddenly, the problem is not due to a misadjusted control though a dirty pot is possible - turn it back and forth - this might clean it and restore normal operation. * Component or connection on CRT neck board - insufficient voltage to or incorrect biasing of the video driver for this color can result in the CRT never totally blanking. Compare voltages and signals, and swap components between good and bad channels to confirm. * Blanking circuit - this may be a part of the video/chroma chip or separate. Check and compare waveforms of good and bad colors to determine if the blanking pulses are making it to the video output. There is a slight possibility that a bad CRT may result in visible retrace lines. To eliminate this possibility: * Disconnect the filament - all evidence of a picture, raster, and retrace lines should disappear once the filaments/cathodes have cooled (15 seconds or so. If there are still visible retrace lines, the CRT is suffering from cold or field emission from someplace (may not even be the cathode). * Turn down the screen (G2) control on the flyback (usually). If one color remains no matter how you set the control, again there is some kind of weird emission from the CRT. However, if white/gray retrace lines remain, the problem may be in the screen supply. See the section: "Bad CRT causing retrace lines".
(From: Jeroen H. Stessen (Jeroen.Stessen@ehv.ce.philips.com)). The TV which I bought last started developing retrace lines after a month or so of use. I took it back to the lab for warranty (special deal) and had it examined by the real experts. They found that even with the filament supply disconnected and VG2 at 0V the screen would still light up. They could even see that the electrons weren't even coming from the cathode. That was with only the picture tube in a test rig. So in this case the obvious conclusion had to be that the tube was bad, and it was replaced (32" 16:9 SF, very $$). It had something to do with processing problems during manufacturing of the electron guns. So even if this was a rare case, it *can* happen that retrace lines are due to a bad picture tube. It's more usual to suspect the VG2 (screen voltage) or a defect somewhere in the RGB video path.Go to [Next] segment
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