I replaced the 2 STK392-110 convergence amps with STK392-180s, and the repair looked good after it was complete. But 4 days later, after several hrs. of the unit being powered on, the convergence went out...
Hi, well I applaud you for wanting to have a go, but you must make sure that you are starting in the right place, That is The Power Supply, as, if, that isn't right nothing else can be. But you simply cannot do anything without a Service Manual. In this it has everything one needs to repair the set. OK if it is shutting down, after that amount of time, of working and then faulting, then it is most definitely a "Thermal" problem, the way we "Find" problems such as this is "Freeze Spray" you use this on each component that is suspected of being the "Culprit" and you will soon,find that errant component. Now also not every fault is a Capacitor, I see many, many people that think, that Capacitors are always the "Culprit" now while that may be true in a few cases, a faulty Electrolytic Cap, or ordinary, Cap goes faulty, this is only a SYMPTOM, something has damaged those caps causing them to "Fail". One MUST always find the root "Cause", otherwise if you just treat, the SYMPTOM, the "Cause" will just make the "Symptom" come back, in short order, as the prime cause still, hasn't been fixed., Now Capacitors hate AC ripple, or Over Voltage. That’s it. Oh.. and Heat, if these Capacitors, are too close to a Heat Source, then that’s a prime cause of failure. Resistors, hardly ever go faulty, and if they do, it is generally obvious. However it doesn't hurt to check values with our Multimeter. Remember though resistors are made, with up to 20% tolerance from stated value, as such, are not too critical, unless in Timing circuits etc. Always check, the Values, of resistors, as with any other component, with the power OFF. Now Diodes especially "Zener Diode", are another thing to check, those and ordinary "Signal Diode" should always be suspect. next we have Transistors and IC's. The Transistors MUST ALL be checked to see if they have a good, "Junction" this is done, with our meter set to "Diode Test" and usually are about 0.6 to 0.7. With IC's you must check, voltage levels, or Logic Levels, going in and out, have a look at the circuit diagram, and it will tell you what they should be. It is a good idea to always measure the Power Supply voltages, see if a "Rail" is Low, that will be because some component has gone somewhat or all short circuit, to Earth, now, if the "Rail" is Higher, suspect an "Open Circuit" component, like a Diode, or Transistor. The voltages expressed in the manual are spot on, ANY variation MUST be investigated. I have been doing all this for over 30 years now, and I do indeed wish, we could have a set of "Symptoms" and be able to say.. "Oh that’s the so-in-so and replace this" however unfortunately this although does happen, most "Symptoms" can have literally tens, of "Causes" all often "Interlinked" One simply has to do a methodical troubleshooting procedure, and always think, "are my Voltages Correct" as this is how, you Fix the problem, by making them so. Keep up the good work. If that link above doesn't furnish, a Service manual, it is imperative you get one, even if you must pay for it. It will pay for itself in about 2 mins.
The Tools you will need are A SERVICE MANUAL a Good Multimeter, a Signal generator, a Signal Tracer, pref an Oscilloscope, Soldering Iron, De-soldering iron, Probably, too, A SMT Hot Air desolderer (for the Surface Mount IC's), Compressed Air, An Anti-Static Wrist Strap, (MOST IMPORTANT, to prevent ESD), Cutters, Screwdrivers, sometimes, Torx, drivers too. Tweezers, are real handy, a magnifying glass, or eyepiece, a good strong white Light. OH, and you MUST have the original remote control too, (Sometimes one must obtain, purchase, a special “Servicing remote”) as one needs this to "Program" the Computer in the TV, after, and during servicing, and to be able to put the TV, into "Service Mode" too.
When servicing try not to let the entire thing overwhelm you as one, treat the set as a conjunction of “Units”. Meaning that we can break the unit up into sections, for instance we have a Power Supply, and Audio section, a Remote Control section, we have a Input Control section, we have a Video Control section, and so on. Now all these connect to specific parts of the circuit. Some have no relationship with each other and some are dependent upon each other. What we need to do is try to understand our “Fault” and isolate it to at least an “Area”. Now when we have isolated the apparent problem, we then need to check our “Input” to that section and also the “Output” of that section, also we must first check that sections supply voltage and current, are correct. Depending on the unit being serviced, the Repair options, may be limited to changing a “Board” to clear the fault. Often these boards are exchangeable, and you get a rebate back, if when you purchase the new board, you send them you old broken board, and they then repair that, and around it goes. Other times, one must go down to “Board level” to effect a repair, always double check, before determining some component is faulty, it is best to isolate/remove, the component to test, often an “in situ” test can give erroneous reading due to “Other” components connected, altering the readings. Always replace with as good if not better components that you are replacing, skimping of component costs is counterproductive, in the long run.
It can often be a great troubleshooting method, to completely isolate the “Faulty” part of the circuit, if you can, isolate the in & out, and also remove, the “Native” power from, it too. You power from and external source, then also you can provide an External “Drive” to this circuit which you will NOW, be able to test under a, “know good” situation, which is so important to gain a benchmark for operation.
NEVER EVER simply replace a Board or Component without ascertaining WHY, it has failed, as seldom does anything spontaneously fail, unless placed under stress at all operating times, such as a power Supply or the like.
Above is a training manual to help you understand what's going on.
Below is your service manual.
Jul 17, 2010 |
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