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Re: where to hook up com neg. lead to check dc volts on...
Most TVs today use a "hot-chassis" design and a switch-mode power supply. You should use an isolation transformer when doing any service work on a TV. This helps protect you and your test equipment, and can prevent accidental damage to the TV by grounding parts to the wrong point.
Hot-chassis sets use two different grounds. The power supplies have one ground reference for the primary side (hot ground) and a different point for the secondary (cold ground). The point you pick will depend on what part of the TV you're measuring.
If you are troubleshooting a dead set and working on the primary side of the power supply, use the negative lead of the large electrolytic capacitor you'll find near the AC input connection. There's almost always a bridge rectifier and filter cap (300 to 400 uF range, 180 to 250 volt rating, so physically pretty large) in that area to make the raw DC. That's a guaranteed good hot ground. Sometimes the set will have a labeled hot ground point right on the circuit board for you.
For measurements on the secondary (output) side of the supply, almost any shield can is ground. The tuner cover is a good choice.
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You need to know if the speaker on the set is good. Try this, with the set turned off, "rig a 1.5 vdc battery with 1 lead to the + and another lead to the - signs. Touch one wire lead to the plus side of the speaker connector and "tap" the other lead to the minus speaker connection.. You should be able to hear a "rasping" sound coming out of the speaker, that is, if the speaker is good. If the speaker is bad, replace it.
If the speaker in the set is good, then check the Audio output transistor and the audio driver transistor. Check for cold solder joints close to and in the vicinity of these two components.
Another alternative to checking the speaker is to get a small AC-DC transformer, like those used to charge your cell phones. Use one that has an output of 1.5 V dc to safely check the speaker(s). Good luck!
Check for blown fuse EP91. If the fuse is blown, check for a shorted IP01 regulator transistor in the deflection power supply. If that is shorted, change the IP04 photo coupler and leaky D05 a 12 volt zener in the OCP circuit of IP01. If this all looks good, look for an oily fluid on the printed circuit boards under the picture tubes. Good Luck
can be ascertained from the power regulator, you can check the
transistor / STR power regulator, and Diode Bridge (AC-DC), check the
Positive and Negative on Elco 220/450 volt power regulator, is there a
short circuit? if no, probably from before entering the diode, it can be from thermistor. Hopefully help
Unfortunately it isn't age that causes these TV's to fault, no, it is the actual Power flowing through them and the heat and stress this places upon every component in any unit. Unfortunately, electronic devices get destroyed by the very thing that makes it function. Either slowly, over time, or suddenly, from a Power Spike, or Surge. This damages the "unlucky" device that is plugged in and turned on. or as said over time the heat stress, and electrical strain, can cause a component to fail. slowly, bit by bit, over time until, it reaches a point, where it fails catastrophically. Well now you know how it all happens. My advice is to get a "Quote" for repair, and that way you can decide on repair, or replacement,
Check power supply transisters possible shorted
and check transister next to ht runs picture may be shorted also check diodes 4off runs ac to dc
changover , this possible causes the fuse to blow , allways be carefull when pluging any
electrical item in
please let me know how you go thanks jeff..........
ARE WE TALKING MANUAL SWITCHING,OR REMOTE? FIRST CHECK POWER GOING TO SET. CHECK THE LED AT FRONT OF SET FAST WAY TO CHECK POWER. IF YOU ASSURE POWER AND STLL NOT WORKING WE NEED TO OPEN UP SYSTEM. CHECK POWER FUSE THEN DC VOLTAGE HERE WE NEED TEST EQUIPMENT.ALSO A GOOD WAY ONCE OPEN BACK DO A SMELL TEST.
electrolitic capacitors can be used in dc and ac circuits as long as you know how to use them. basicly a cap is a fast charging and discharging battery. it is designed to hold charges steady in a cicuit. they have a positive side and a negitive side. donot reverse the polls or you will have an exploding cap. the cicuit that these caps are in is a dc cicuit (24 volts to the panel).
the caps again are 2200uF 35 volt with a temprature rating of 105 degrees C.
you can get them at www.mcminone.com part number 31-5745. remember DONOT REVERSE THE POLLS!! there is a strip down the side with negitve signs in it that corespond to the negitive lead. the board will have the polls printed on it or at lest om of them.
First of all check the power socket is working, by plugging something different in.
Do you have fuses in plugs in the USA, like in the UK?-Check this.
If you can remove the back and are safe using a voltmeter, then clip the leads where the mains should be inside the set, then plug the mains in.
I say `clip' the leads on for safety, so you can keep your hands clear of any exposed voltages on the circuit boards.
If you cannot find anywhere to clip to, I would advise soldering a length of insulated wire to attach the meter to, before plugging in the mains.
Depending which side of the mains on off switch you are you should see a reading if all is well so far.- Try the on off switch in the set.
If this is OK then go a stage further and see if there is any voltage the other side of the mains rectifier. This will be about 150 volts DC in the USA, and about 350 volts where the mains is 240 volts AC.
If this is OK then you have a more serious problem, as it most likely in a short circuit line output transistor and will need a service engineer.
Check to see while tracing the circiut so far if there is a fuse.
Check if you can to see if the `reservoir' capacitor is short circuit or faulty- this is the capacitor just past the rectifier.
If you find one thing wrong and can replace it, you will nearly always find there is another component wrong, which caused the replaced component to go wrong also,-so beware!
Well good luck.
I am sure it can be repair,Checking the fuse was good idea but it seems the problem might be farther ahead,if you have no indication of power(no lights,no clicks)the problem might be in the power supply,there is a 5 volts supply that has to be running because is the power to the microprocessor(brain)and when you push the power button on the remote or the set the brain knows it and send the commands to everyone else to turn on,if you have the 5 volts and the brain is working the problem might be in the horizontal circuit ,possibly a bad horizontal output transistor(shorted)if he is bad it might have taken a fuse or a safety resitor.Some fuses dont look like the average fuse,they look more like resistors.If you are familiar with tv service We can give you all the help you need to find the problem ,if you are not too familiar with servicing electronics you might want to call servicer.Let Us know if you need more information.
Do you know how to work on solid state electronics? if not then Im sorry to say you will need to get the assistance of a local tech who is experienced. As these sets are solid state and there are no user servicable parts inside. Good Luck