la service manual – Datasheet PDF, IC Circuit. USOC(LA) SERIES SERVICE MANUAL Table of Contents 1. Preface. Find solutions to your la 7n datasheet question. Get free help, tips & support from top experts on la 7n datasheet related issues. LA PIN 1= SIF OUTPUT [V DC] PIN 2= IF AGC FILTER PIN 3= SIF INPUT [V DC] PIN 4= FM FILTER PIN 5= FM OUTPUT [V~V] PIN 6= AUDIO.
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Chapter One Power Supply Chapter Two Horizontal Deflection. Chapter Five Typical Datashewt Analyse. This applies mostly to TV s, computer and video monitors, some AC operated strobe lights, and other line connected devices. You should not be touching components with the device powered and plugged in at leastnot until you really know what you are doing!
Once unplugged, sheet metal shields or other ground points should be safe and effective. Safety first – know the hazards associated with the equipment you are troubleshooting. Take all safety precautions. This is applied both to the analytic procedures as well as to precautions with respect to probing the equipment. Learn from your mistake.
We all make mistakes – some of them can be quite costly. A simple problem can turn into an expensive one due to a slip of the probe or being over eager to try something before thinking it through.
While stating that your experience in these endeavors is measured by the number of scars you have may be stretching the point, expect to screw up – we all can point to that disaster due to inexperience or carelessness.
Just make it a point not to make the same mistake again. Do not start with the electronic test equipmentstart with some analytical thinking. Many problems associated with consumer electronic equipment do not require a schematic though one may be useful. If you get stucksleep on it.
Sometimesjust letting the problem bounce around in your head, will lead to a different more successful approach or solution. Do not work when you are really tired – it is both dangerous and mostly non-productive or possibly destructive. Many problems have simple solutions. Do not immediately assume that your problem is some combination of esoteric complex convoluted failures.
For a TV, it may just be a bad connection or failed diode. Try to remember that the problems with the most catastrophic impact on operation- a dead TV usually have the simplest solutions. The kind of problems we would like to avoid at all costs are vatasheet ones that are intermittent or difficult to reproduce: Whenever possible, try to substitute a working unit.
Datashee modular systems like component stereos and computers, narrowing down a problem to a single unit should be the first priority. This is usually safe to do in such case and will quickly identify which unit need work. This same principle applies at the electronic.
la76931 service manual – Datasheet PDF, IC Circuit
Note that there is the possibility of damaging the known good part by putting it into a non-working device or vice versa. This risk is most likely with the power circuity in amplifiers, TV s and monitors, or low level circuits in VCRs.
Your frequency counter may be double triggering due to noise or imperfect signal shape. Do not blindly trust your instruments. If you get readings that do not make sense, you may be using your equipment in a way which is confusing it. Your scope may be picking up interference which is swamping the low level signal your are searching for. Realize the coincidences do happen but are relatively rare. Usually ,there is a common cause.
For exampleif a TV has no vertical deflection and no picture it is much more likely that a common power supply output has failed than for parts in both the deflection and video subsystems to be bad. Confirm the problem before diving into the repair. It is amazing how many complaints turn out to be impossible to reproduce or are simple cockpit error.
It also makes sense to identify exactly what is and is not working so that you will know whether some fault that just appeared was actually a preexisting problem or was caused by your poking. Try to get as much information as possible about the problem from the owner. Get used to the idea of working without a schematic.
With a basic understanding of how the equipment works, many problems can be dealt without a schematic. Whenever working on precision equipmentmake copious notes and diagrams. You will be eternally grateful when the time comes to reassemble the unit. Most connectors are keyed against incorrect insertion or interchange lengths or have slightly different thread types. Little parts may fit in more than one place orientation. Select a work area which is wide open, well lighted and where dropped parts can be located – not on a deep pile shag rug.
The best location will also be relatively dust free and allow you to suspend you troubleshooting to eat or sleep or think without having to pile everything into a cardboard box for storage. The function of the voltage power supply is to take the AC line input and produce various DC voltages.
In all casethe power to the horizontal output transistor HOT of the horizontal deflection system is obtained directly from the DC voltage power supply. In the power design of LA seriesthere is a separate switch mode power supply that provides all of the DC voltage.
There will be always be: It enable to turn on or off the main power. A set of rectifiers – in a bridge configuration – to turn the AC into DC. Small ceramic capacitors are place across the diodes to reduce RF interference.
la service manual – Datasheet PDF, IC Circuit |
One large filter capacitor to smooth the unregulated DC. In TVit need switching typical power to provide stable DC. A degauss control circuit including a Posistor a combination of heater disk and Positive Temperature Coefficient PTC thermistor in a single package.
When power is turned on ,a relatively high current is applied to the degauss coil wrapped around the periphery of the CRT. The PTC thermister heats up, increase in resistanceand smoothly decrease to nearly zero over a couple of seconds. A standby power supply for the microcontroller and remote sensor.
(PDF) LA76931 Datasheet download
It derives from the DC voltage power supply. Always use an isolation transformer when working on a TV because this is especially important-for your safety – when la7693 with the non- isolated line operated Power supply. Even so, it may not blow as a result of faults down the line – the fusable resistor or regulator may fail first. The main bridge rectifier is composed of 4 discrete diodes VDVD but may also be a al76931 unite. Failures – usually shorted diodes-are common.
The main filter capacitor C is very important.
Its value is therefore not critical. One arrives the collector of V through pin3 and pin7 of T, the other arrives the base of V through startup resistance R, R,Rlimiting resistor R The startup current cross the B-E of V and make it working in the amplificatory condition.
The current Ic will increase, it causes the inductive voltage increases. The process is shown below: It will undergo a linear increasing process. In this processthe current variational ratio supports the constantly charge voltage. This is the flat-top period of self – excitation pulse.
The current in the base of V Ib also decreases simultaneously. This make the current between pin3 and pin7 of T51 1 to decease. The diverse current flow back pin1 of T via R In this process, Ug does not put any current in the base of V, on the contrary, decreases the startup current of V rapidly.
Vhave to shut down. This means finishing the behind porch of pulse. Although V completely shut down, the current across pin3 and pin7 still exists and decreases rapidly through C and R Ug charge C reversely. The shut-up condition of V is still maintained.
This is called flat-bottom period or pulse interval. Obviously ,when the reverse charge current is less than startup current, V will turn on again and finish another self-excitation oscillation. The self-excitation oscillation circuit repeat again and again and produce switchmode signal about 40Khz. We can see that the switchmode pulse on base of V derive from itself including V,T It is not generated by special circuit.
So we call it self-exiciation. The variational current produces all kind of pulse voltage in all coils l of T including positive feedback coil pin1-pin2.
LA Datasheet –
The safety of the television will be effected while the voltage was changed So we must adopt regulative circuit to ensure the stabilization of the output voltage. When V is onthe current flows through pin3 and pin7 of T, then be converted magnetic energy to be stored. The magnetic energy s strength corresponds with the V s condition. The switch on time more longerthe energy magnetic stored in T will be more stronger.
The inducted voltage pin10 – pin16 will be more higher. On the contrary conditionit just reverse. Regulator is based on the above theory.