TUNER PROBLEMS AND SOLUTIONS.

No reception from antenna or cable:

Make sure your source is providing a signal and that the cable connectorsare good (center pin not broken or bent). Try another TV if possible. Make sure you source select switch or mode is set correctly. Someonemay have accidentally set it to direct video or AUX input. Are all bands affected? If so, the tuner or IF is faulty. If there isa lot of snow, then it is probably toward the front (circuitry wise) ofthe tuner. If it is just a black screen, then it could be in the IF orvideo amplifier. If only certain bands are bad - channels 2-6 for example, then certainparts of the tuner circuitry are faulty. However, make sure the CATVmode is set correctly as this affects reception on a band-by-band basis. The problems may be due to bad solder connections of the tuner shields,connectors, coils, and other components. Try prodding the tuner to seeif you can make the problem come and go or at least change.

Missing or noisy channel or block of channels:
If you are unable to receive certain channels or blocks of channels,this is a tuner problem - could be as simple as bad connections - oreven simpler:. First, check to see that the tuning mode is correct - TV, CATV, asthis is the most common cause of channels 'disappearing'. TV channels are assigned frequencies ranging from 72 to almost 800 MHzdepending on broadcast or cable channel assignment. To tune over such a wide range requires splitting it up into various bands even if these are not actually defined. If you have a varactor tuned set, then you already know about the Vl, Vh, and U bands which may use separate front-end components. Even modern quartz PLL synthesized tuners need to allocate circuitry depending on frequency range. Therefore, if a block channels is not working, it could be due to a failure of some component related to that frequency range. Aside from looking for bad connections, resoldering the shields and connector pins, prodding, pressing, praying, etc. you will need a schematic to have any chance of finding such a fault. There is another slight possibility. Some TVs have a parental lockoutcapability (pre V-chip) to prevent kids or other unauthorized access toselected channels. The channel selections may have been accidentallyaltered. Check your user manual for instructions on programming thisfeature. Even on models without this option, the same internal circuitry could be present but not normally accessible. A power surge or stray cosmic ray could have put the set in a screwy mode. Unplugging power for a minute or probably a much longer time might possibly reset such an anomaly.

Loss of Channel after Warmup:
If there is a general loss of picture and sound but there is light on the screen, then most likely the tuner or IF stage is pooping out. With both no sound and no picture but a raster and static, it is mostlikely a problem in the tuner, power to the tuner, or its controller(if non-knob type). If it recovers after being off for a while, then you need to try a coldspray in the tuner/controller to identify the component that is failing.Take appropriate safety precautions while working in there! If it stays broken, then most likely some component in the tuner, itscontroller, or its power supply as failed. There is a slight chance that it could be a bad solder connection - I have seen these in the tuner modules of RCAs on several occasions (and many other manufacturers – apparently not a solved manufacturing problem even after 40+ years! Channel tuning drifts as set warms up: This may be a slight drift - like someone is messing with the fine tuning or such a substantial change in tuning frequency that the channels go by as though you are surfing. Possible causes depend on tuner type:
1. Quartz tuner (10 button direct access digital synthesizer) - For a slight drift, a component is probably changing value, possibly the crystal in the reference oscillator. For gross changes - flipping through channels - it is more likely to be a digital control problem -the microcontroller is misdirecting the synthesizer to change frequency.
2. Varactor tuner (buttons but not direct channel access) - If only a single pushbutton selection is the problem, the the varactor tuning diode for that button is probably changing capacitance. If all channels ina band (Vl, Vh, U) are having a problem, it is more likely to be a drifting D/A or faulty AFT (Automatic Fine Tuning) circuit or power supply.
3. Turret or switch tuner (Knobs) - A component like a capacitor is changing value. You will have to get in there with a heat gun or cold spray and track it down the old fashioned way. At least, the problem is almost certainly localized to the tuner box (and possibly the controller if applicable). As noted, gradual slight changes in tuning are likely due to frequencydetermining components drifting. Uncontrolled channel surfing is probably a logic problem. For thequartz tuner, this could still be marginal connections causing themicroprocessor to misdirect the synthesizer to change channels. For the latter case, particularly, the cause may still be bad connections resulting in loss of channel memory and/or erratic behavior.

No reception from antenna or cable
Make sure your source is providing a signal and that the cable connectorsare good (center pin not broken or bent). Try another TV if possible. Make sure you source select switch or mode is set correctly. Someonemay have accidentally set it to direct video or AUX input. Are all bands affected? If so, the tuner or IF is faulty. If there isa lot of snow, then it is probably toward the front (circuitry wise) ofthe tuner. If it is just a black screen, then it could be in the IF orvideo amplifier. If only certain bands are bad - channels 2-6 for example, then certainparts of the tuner circuitry are faulty. However, make sure the CATVmode is set correctly as this affects reception on a band-by-band basis. The problems may be due to bad solder connections of the tuner shields,connectors, coils, and other components. Try prodding the tuner to seeif you can make the problem come and go or at least change. Picture is overloaded, washed out, or noisy This indicates an Automatic Gain Control (AGC) problem often caused bya dried up capacitor. You will probably need a schematic to go muchfurther. This could be a problem in the tuner, IF, or video amplifiers.

Interference when using VCR RF connection
(Some of these comments also apply to use of Laserdisc players, satellitereceivers, video games, or other sources with RF modulator (Channel 3/4)outputs). This may consist of patterns or lines in the picture. If this only happens on the antenna or cable, it may be a problemwith these sources or the tuner in the VCR rather than the TV.As a test, try the connecting the TV directly to the antenna or cable. If it only happens on cable, there may be a (temporary) problem withcable transmission - contact your cable company. If it happens on playback of good quality (commercial) recordings, thenit could be a compatibility problem between the VCR and TV. Make sure your patch cable connections are secure and that the cablesare not damaged - in particular that the center pin is intact. Try fine tuning if your TV has this capability. If this does nothelp, try switching the channel 3/4 selector on the VCR to the oppositeposition and try that channel, sometimes one will be better than the otherparticularly if one of these or an adjacent channel is active in your area. If you have RCA baseband video inputs on your TV, try this connection tothe VCR. These should work better in any case. Confirm that it is not actually a problem with the VCR - try another TVif possible. If you just changed your component placement, the VCR or TV may bepicking up interference from another component. Turn off everything butthe VCR and TV and see if that identifies the culprit. Move the TVaway from the VCR so see if they are interfering with each other - theTV may be introducing interference into the VCR. Occasionally, the particular patch cable or its length may affectreception quality - try another one. If none of this helps, you VCR's RF modulator may be bad or slightlyweak. Alternatively, the tuner in the TV may be faulty. If receptionis generally noisy on all sources, AGC or RF/IF alignment may needadjusting. However, not all tuners are created equal. Your TV maysimply be making the best of a marginal situation. A light dimmer on the same circuit as the TV may result in similarsymptoms. If you are tuning up your motorcycle (or automobile) in thesame room, this may be spark ignition interference.

Missing or noisy channel or block of channels
If you are unable to receive certain channels or blocks of channels,this is a tuner problem - could be as simple as bad connections - oreven simpler:. First, check to see that the tuning mode is correct - TV, CATV, asthis is the most common cause of channels 'disappearing'. TV channels are assigned frequencies ranging from 72 to almost 800 MHzdepending on broadcast or cable channel assignment. To tune over such awide range requires splitting it up into various bands even if these arenot actually defined. If you have a varactor tuned set, then you alreadyknow about the Vl, Vh, and U bands which may use separate front-endcomponents. Even modern quartz PLL synthesized tuners need to allocatecircuitry depending on frequency range. Therefore, if a block channels isnot working, it could be due to a failure of some component related to thatfrequency range. Aside from looking for bad connections, resoldering theshields and connector pins, prodding, pressing, praying, etc. you will needa schematic to have any chance of finding such a fault. There is another slight possibility. Some TVs have a parental lockoutcapability (pre V-chip) to prevent kids or other unauthorized access toselected channels. The channel selections may have been accidentallyaltered. Check your user manual for instructions on programming thisfeature. Even on models without this option, the same internal circuitrycould be present but not normally accessible. A power surge or stray cosmicray could have put the set in a screwy mode. Unplugging power for a minute or probably a much longer time might possibly reset such an anomaly. Loss of Channel after Warm up If there is a general loss of picture and sound but there is light on thescreen, then most likely the tuner or IF stage is pooping out. With both no sound and no picture but a raster and static, it is mostlikely a problem in the tuner, power to the tuner, or its controller(if non-knob type). If it recovers after being off for a while, then you need to try a coldspray in the tuner/controller to identify the component that is failing.Take appropriate safety precautions while working in there! If it stays broken, then most likely some component in the tuner, itscontroller, or its power supply as failed. There is a slight chance thatit could be a bad solder connection - I have seen these in the tuner modulesof RCAs on several occasions (and many other manufacturers - apparentlynot a solved manufacturing problem even after 40+ years!

Channel tuning drifts as set warms up
This may be a slight drift - like someone is messing with the fine tuningor such a substantial change in tuning frequency that the channels go byas though you are surfing. Possible causes depend on tuner type: Quartz tuner (10 button direct access digital synthesizer) - For a slight drift, a component is probably changing value, possibly the crystal in the reference oscillator. For gross changes - flipping through channels - it is more likely to be a digital control problem - the microcontroller is misdirecting the synthesizer to change frequency. Varactor tuner (buttons but not direct channel access) - If only a single pushbutton selection is the problem, the the varactor tuning diode for that button is probably changing capacitance. If all channels in a band (Vl, Vh, U) are having a problem, it is more likely to be a drifting D/A or faulty AFT (Automatic Fine Tuning) circuit or power supply. Turret or switch tuner (Knobs) - A component like a capacitor is changing value. You will have to get in there with a heat gun or cold spray and track it downthe old fashioned way. At least, the problem is almost certainly localizedto the tuner box (and possibly the controller if applicable). As noted, gradual slight changes in tuning are likely due to frequencydetermining components drifting. Uncontrolled channel surfing is probably a logic problem. For thequartz tuner, this could still be marginal connections causing themicroprocessor to misdirect the synthesizer to change channels. For the latter case, particularly, the cause may still be bad connectionsresulting in loss of channel memory and/or erratic behavior.

Noise in picture and sound due to bright scene
When a bright scene comes, the screen flashes and there is a lotof noise in the sound. When a dark scene comes, there is no flash or noise. Changing channel does not help. The noise persists even when the sound is muted. (The following is from: Lattuca@Midwest.net (Sam Lattuca)) When the video detector level is adjusted too high, you will get noise in the sound while screen contains a lot of white information (i.e. letters) but won't when only dark scenes are present. The video level adjust is usually a small coil normally located near the IF section. Since your set is several years old, this wouldn't be uncommon. It can be adjusted while watching the picture and listening to the sound.


REFERENCE:
http://www.stedmundsbury.gov.uk/sebc/play/tvprobs.cfm.
http://www.epanorama.net/links/repair.html#tv.
http://www.basementarcade.com/arcade/library/tvrepair.txt