LG 710E 17″ CRT Keep track of came in with the grievance of ability blink. A ability blink dilemma can be lead to by either in most important or secondary part or even in both equally sections.
A faulty ability IC, electrical power fet breakdown when underneath load, higher esr in electrolytic capacitor, increased in present-day perception resistor benefit, a shorted zener diode, a leaky transistor, open up circuit or resistor has transformed value in major side can result in electric power to blink. As for the secondary facet, a shorted secondary diode, flyback, Hot, horizontal yoke coil, damper diode, B+ fet, an open up filter capacitor, shorted IC and and so forth can lead to energy to blink as perfectly.
Commonly what I do is to take away the B+ fet initially and link a light bulb to distinguish regardless of whether is the major or after the B+ circuit components that caused energy to blink. Even so in this scenario, I did not place the mild bulb and I instantly eradicated the B+ fet and electrical power on the keep an eye on. For your info, this B+ fet is the N-channel mosfet and this B+ fet is element of the strengthen circuit.
Right after eliminating the B+ fet, not only the ability didn’t blink, there was exhibit as effectively and the anode voltage reads about 12 Kilo volt (a great observe really should have about 24 KV). The rationale why you acquired 12 kilo volts is simply because the improve circuit is not functioning thanks to the removal of the B+ fet. The show demonstrated a tiny width and the horizontal measurement management is already set to the greatest (you cannot get optimum width for the reason that the anode voltage is only 12 KV). You can management or established every thing in the On Monitor Screen (OSD) except you can’t carry horizontal dimensions to highest.
With having a display screen, it is a fantastic clue to me simply because I knew that a lot of circuits is functioning this kind of as electric power area (so you never suspect principal side anymore), flyback transformer, yoke coils, micro-p, eeprom, horizontal and vertical circuit, colour circuit and even the Osd circuit. With out the B+ fet, there is exhibit but with B+ fet the electric power blink. In this circumstance, one would generally look at the B+ fet first am I right? Nevertheless the B+ fet turned out to be fantastic!
Now where by is the perpetrator hiding? Troubleshooting sometimes can be extremely discouraged and most of the time is often enjoyment. Just one of my strategies that I appreciated to use is to contact for any unusually hot parts on board with my finger. (Please choose observe for all electronic repairers-change off and unplug the ability cable and discharge the huge filter capacitor in primary aspect prior to you get started to touch any parts).
Normally soon after energy off, I would touch on the flyback initially then to other parts bordering the superior voltage part. When searching the factors with my finger I stumbled on a resin coated ceramic disc capacitor which is fairly scorching. It is found around the flyback transformer and in truth the capacitor was there is to act as a filter capacitor for the 400 vdc line output as revealed from the image.
Soon after the cap was taken off and checked with an analog meter, it showed a shorted reading even in the X1 ohms array. A fantastic capacitor really should display a charge and discharge action in the X10 k ohms array. A new capacitor replacement for this LG 710E 17″ CRT Keep track of remedied the fault.
The explanation why the observe electric power blinks is since the faulty capacitor become shorted when in complete operating voltage (raise circuit is functioning and about 60 -70 vdc enter the B+ flyback pin).
When the B+ fet was removed (raise circuit not functioning and only about 40 vdc enter the B+ pin of flyback) the observe is not working beneath whole operating voltage and the defective capacitor can still tolerate (partial limited) and turned hot. I think if the check is switched “on” for a minor longer, it would lead to the capacitor to develop a immediate small circuit and if this come about, taking away the B+ fet to examination the keep track of would not make any unique (the electrical power would however blink).
