TV POWER SUPPLY PROBLEMS AND SOLUTIONS .

TV power cycling on and off:


The power light may be flashing or if you are running with a serieslight bulb it may be cycling on and off continuously. There may bea chirping or clicking sound from inside the set. (Note: using too small series light bulb load during testing for the size of the TV may also result in this condition.) If there is a low voltage regulator or separate switching supply, itcould be cycling on and off if the horizontal output, flyback, orone of its secondary loads were defective. Does this TV have a separate low voltage regulator and/or switching power supply or is it all part of the flyback circuit? For the following, I assume it is all in one (most common). Some simple things to try first: Verify that the main filter capacitor is doing its job. Excessive ripple on the rectified line voltage bus can cause various forms of shutdown behavior. An easy test is to jumper across the capacitor with one of at least equal voltage rating and similar capacitance (make connections with power off!). Use a Variac, if possible, to bring up the input voltage slowly and see if the TV works at any point without shutting down. If it does, this could be an indication of X-ray protection circuit kicking in, though this will usually latch and keep the set shut off if excessive HV were detected.


TV turns off after warming up:



If you can turn it back on with the s momentary key or power button: When it shuts off, do you need to push the power button once or twiceto get it back on? Also, does anything else about the picture or soundchange as it warms up?

1. If once, then the controller is shutting the TV down either as a result of a (thermally induced) fault in the controller or it sensing some other problem. Monitoring the voltage on the relay coil (assuming these is one) could help determine what is happening. The controller thinks it is in charge.

2. If twice, then the power supply is shutting down as the controller still thinks it is on and you are resetting it. A couple of possibilities here would be low voltage or high voltage regulation error (excessive high voltage is sensed and causes shutdown to prevent dangerous X-ray emission). A partially dried up main filter capacitor could also cause a shutdown but there might be other symptoms like hum bars in the picture just before this happened. Clipping a good capacitor across the suspect (with power off!) would confirm or eliminate this possibility. If it uses a pull-knob (or other hard on/off switch), then this may be like pulling the plug and would reset any abnormal condition.



TV doesn't power up immediately:


The TV may do nothing, cycle on and off for a while, power up and thenshutdown in an endless cycle - or at least for a while. Then it comeson and operates normally until it is turned off. A couple of possibilities:

1. The main filter capacitor or other filter capacitors in the low voltage power supply is dried up and this can cause all kinds of regulation problems.

2. The power supply regulator is defective (or marginal) allowing excessive voltage on its output and then the X-ray protection circuitry shuts you down. If you can get access to a Variac, it would be worth bringing up the input voltage slowly and seeing if there is some point at which it would stay on. If there is, then if the picture has serious hum bars in it the main filter cap could be bad. If more or less a decent picture with minor hum bars then it could be the regulator.


Arcing from flyback or vicinity:


Arcing may be visible or audible and result in readily detectable levels of ozone. Note that very slight traces of ozone may not indicate anything significant but if the TV smells like an office copier, there is probably some discharge taking place. WARNING: It is possible for arcing to develop as a result of excessive high voltage. Symptoms might be a smaller than normal excessively bright picturebut this may not be able to be confirmed until the flyback is repaired or replaced. See the section: "Excessive high voltage".

* On the HV output, it will probably be a loud snapping sound (due to the capacitance of the CRT) with associated blue/white sparks up to an inch or more in length. If the arc length is short enough, this may turn into a nearly continuous sizzling sound with yellow/orange arc and melting/burning plastic.

* Prior to the HV rectifier, it will likely be a continuous sizzle with orange/yellow/white arc and melting/burning plastic or circuit board material.

* Internal arcing in the flyback may be audible and eventually result in a bulging and/or cracked case (if some other component doesn't fail first as this would take some time to develop).

* A corona discharge without actual sparks or a visible well defined arc is also possible. This may be visible in a totally dark room, possibly more likely when the humidity is high. A thorough cleaning to remove all dust and grime may be all that is needed in this case.

* If the arc is coming from a specific point on the flyback - a crack or pinhole - this may be patched well enough to confirm that the rest of the TV is operational and a new flyback is worth the money. Otherwise, there is no way of knowing if the arcing may have damaged other circuitry until a replacement flyback - possibly money wasted - arrives. To attempt a repair, scrape off any dirt or carbon that is present along the path of the arcing and its vicinity. Then, clean the area thoroughly with alcohol and dry completely. Otherwise, the dirt and carbon will just act as a good conductor and the arcing will continue under your repair! Several layers of plastic electrical tape may be adequate for testing. Multiple coats of high voltage sealer or non-corroding RTV silicone (if it smells like viniger - acetic acid - as it cures, this may get in and affect the windings) would be better if the objective is an actual repair. This may prove to be a permanent fix although starting the search for a source for a new flyback would not hurt just in case. The arc most likely did damage the insulation internally which may or may not be a problem in the future. Also see the section: "Dave's complete procedure for repair of an arcing flyback".
* In some cases, the pinhole or crack is an indication of a more serious problem - overheating due to shorted windings in the flyback or excessive secondary load.

* If the arc is from one of the sparkgaps around the CRT or the CRT socket, this could also be a flyback problem indicating internal shorts in the focus/screen network.

* If the arcing is inside the CRT, this could indicate a bad CRT or a problem with the flyback focus/screen network and no or inadequate sparkgap protection. Where repair seems possible, first, clean the areas around the arc thoroughlyand then try several layers of plastic electrical tape. If the TV works normally for say, an hour, then there is probably nothing else wrong and youcan try for a proper sealing job or hope that tape holds out (put a few more layers on - each is good for about 8-10 KV theoretically). However, replacement of the flyback really is the best alternative to minimizerisk of future problems. This is the only option where there could be a potential issue of liability should subsequent failure result in a fire. Once I had a TV where the main problem was a cracked flyback arcingbut this took out one of the fusable resistors for the power supply to the *vertical.* output so the symptoms included a single horizontal line.Don't ask me to explain - replacing that resistor and the flyback (theflyback tested good, but this was for someone else) fixed the TV. In another case, a pinhole developed in the flyback casing probablydue to poor plastic molding at the time of manufacture. This resulted in a most spectacular case of sparking to a nearby bracket. A few layers of electrical tape was all that was needed to affect a permanent repair


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