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Handy Electronics Youtube Videos
! TV Repair: [Dave's TV in Grants Pass, OR|http://www.youtube.com/user/GrantsPassTVRepairs] * [Video #1|http://www.youtube.com/watch?v=GryA_Zl4EBk] ** Checking for bad caps by looking for bulges, but it's better to use a capacitor checker (reputable ones: [Cap 88 Equivalent Series Resistance (ESR) Meter|http://www.drillspot.com/products/75537/BK_Precision_881_IN-Circuit_Esr_Dcr_Capacitor_Tester?s=1]by Electronic design; Capacitor Wizard; Blue ESR Meter) ** Replacing with different capacities is iffy, but you can go up in voltage (and this can sometimes be a great idea) ** Remember capacitance decreases in series and adds in parallel ** Make non-polarized capacitors by putting two polarized in opposite directions (?? - verify) ** Use a flashlight to see through the back of a PCB ** [TV repair case histories|http://www.mikestvtips.com] (!) Something like this for radios? * [Video #2|http://www.youtube.com/watch?v=eJ2FTxxOqxs] ** Hairdryer to heat up components to test for intermittent overheating effects ** Freeze spray for the opposite ** Telephone earplug-inductive coil amplifier device - can listen for magnetic oscillations (e.g., 60Hz hum, switched-mode power supply) ** Small neon bulb - can be used to detect high voltage (e.g., flyback transformer) * [Video #3|http://www.youtube.com/watch?v=R_uBSzIgO5M] ** Don't buy excessively cheap components * [Video #4|http://www.youtube.com/watch?v=tEgV1MjlmoY] ** Bad fuse is probably because of too much current draw within the circuit itself (as opposed to a fluke surge) ** Sub in a circuit breaker while the fuse is still popping ** Variac to slowly ramp up power ** Light bulb in series on AC line as debugging aid (demonstrates short circuit) ** Inductive Ammeter (AC only) *** Looping wire around clamp multiplies the amp reading (= more sensitive reading) * [Video #5|http://www.youtube.com/watch?v=TXGxE9Fxhlw] ** Heat temporarily improves a capacitor's quality rating, freezing lowers it ** Resistors increase under heat ** If taking a hairdryer to a circuit is enough to make it work, then it's probably a bad capacitor * [Video #6|http://www.youtube.com/watch?v=SCUVBYaMi9Y] ** [Switched-Mode Power Supply Troubleshooting|http://www.powersupplyrepairguide.com/] ** Choosing correct Ground Reference Points *** Different ground symbols (e.g.: hot-ground/3-lines, isolated-ground/hollow triangle) *** Separations in PCB can be a good clue ** Measure on rectified side, not on high-frequency AC side * [Video #7|http://www.youtube.com/watch?&v=OFqLAIqiHMo] ** Finding bad solder joints *** Requires attention to detail, magnification (e.g. loupes, old camera lenses) *** A clue is darkened areas where excess heat may be *** When in doubt, just re-solder ** Sand bad leads/pads, or possibly make your own access and use a jumper wire ** Always discharge big caps before working with circuit ** May be cracks if board has been jolted/dropped - can be very difficult to spot * [Video #8|http://www.youtube.com/watch?v=EjMLEPGJY2o] ** Shut-downs are a common circuit response to any problem ** Talks about LCD backlights a bit (e.g., recommendation to salvage them off of old monitors) ** Good debugging sequence starting at 3:11 - No power at terminals, found transformers, turned out to be xformer controlling xistor ** Check transformers for shorts with a coil tester AKA coil ringer (DIY?) (see video #10 tip) * [Video #9|http://www.youtube.com/watch?v=0O5v89lEHxA] ** Varying brightness on TV = varying beam current = varying power draw ** Hot-running IC might be a problem (try freeze spray) ** Compare power draw to back of TV's expected draw (varies with picture, though). High draw is probably a component problem. ** Watt-meter + Variac = handy. Circuit problems can cause jumps in power disproportionate to voltage change (e.g. PSU problem) ** Slowly turning up variac is a good check of voltage regulator - by definition it should not change much with increased voltage ** Wear ground strap (or manually neutralize) * [Video #10|http://www.youtube.com/watch?v=EDylk9ezQtA] ** Checking transformer with a VOM *** Test resistance across coil windings for a sketch *** A coil tester is better *** Ensure no shorts between primary and secondary windings ** Switched-mode Power Supplies are common problem *** Feedback circuits are the complicated part of an SMPS *** Knowing as much as you can (see link in Video #6) about SMPS and inverters *** Very servicable ** Think in terms of block diagrams (starts at 5:38) *** E.g.: Power Supply board, microcontroller unit (MCU), T-con (controller board), driver ICs (drive screen), screen, backlight & its inverter board, feedback circuits (tell PSU/inverter board to shut down if problem), audio amp, Tuner, *** Know approximate voltages at various block *** Learn when to bail out or escalate ** "Make yourself like a flow chart" (!) * [Video #11|http://www.youtube.com/watch?v=2urDrzpNeW0] ** You'll have to use a frequency counter to check a transformer if transformer frequency is too high for the Audio Amp + Inductive Pickup Coil trick to work ** Nifty coil-to-probe trick to check for stray RF (good for multimeter on freq counter mode and on oscilloscope) ** Neon light for high voltage transformers ** Can check backlight by gently pressing screen * [Video #12 - Repair Process|http://www.youtube.com/watch?v=BsR5LuDrqjI] ** If Dead: *** Check fuse *** Check standby power (that microprocessor draws even when it's off.) by measuring voltage across power switch. *** Check that power supply is getting pulse from mainboard when pressing power button (using oscilloscope between Gnd and the various pins connecting the mainboard and the power supply) ** Ask about symptoms before it went out (e.g., if half the screen was dark, suspect the backlight) ** After a while you have to get a schematic, e.g., from [Sams Technical Publishing|https://www.samswebsite.com/] *** Using a schematic ["can be quite fun at times, other times quite aggravating"|http://www.youtube.com/watch?v=BsR5LuDrqjI#t=4m32s] *** Check voltages *** Check powered-off resistances if labeled *** Perhaps just write a bunch of voltages down then compare to the schematic *** Remember to use ground from the cold side (noticeable by division of PCB), maybe just solder wire to ground ** You want to be more than just a part-exchanger ** Should be able to read common circuits without schematic (e.g., switched-mode power supply) *** [Example overview of power supply|http://www.youtube.com/watch?v=BsR5LuDrqjI#t=7m09s] **** AC input, fuse, chokes to clean up noise, to bridge rectifier, main reservoir cap, into main switching transformer (switched by transistor), secondaries feed into other (smoothing?) caps * [Repairing Remote Controls|http://www.youtube.com/watch?v=xvJWqf_b6Eo] ** Open with a chisel, twisting. ** Often problems are just things spilled on the remote -- clean by disassembly + washing in water + dry with compressed air or hairdryer ** If IR Led = out, test with dedicated tester, a video recorder, or funky reflective strip ** If Driving Circuitry = good, it should emit RF noise, testable with an AM radio ** Possible bad connections, corroded battery connections (sandpaper, then drop of oil) * [Playing with LCD, Polarized Filters|http://www.youtube.com/watch?v=LHKDh_hjeRs] * Also: [Watertown TV Repair|http://www.google.com/search?hl=en&q=watertown+tv+repair&aq=f&aqi=&aql=&oq=&gs_rfai=] Then there's John from Preher-Tech, who moves faster and zips past more details (though he does drop more advertisements): * [Intro to major circuits PSU, Inverter, Main Board, LCD Controller Board, Misc|http://www.youtube.com/watch?v=wMlF_P7zV3U] ** Mentions [CCFL|http://www.betterbulb.com/] (cold-cathode flourescent) for backlight ** Feedback circuits everywhere to shut down in event of trouble ** LCD Controller Board ("T-Con"?) * [Part 2, more misc + LCD itself, Backlight|http://www.youtube.com/watch?v=vLZfpiFD6Ww] * ...the follow-up videos are long overdue.
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Last changed: 2010/11/02 18:31