How To Repair LG 710E CRT Monitor With Power Blink Problem

Last update in December, 2022

LG 710E 17″ CRT Watch came in with the grievance of electricity blink. A electricity blink issue can be trigger by both in principal or secondary portion or even in equally sections.

A defective ability IC, electrical power fet breakdown when beneath load, higher esr in electrolytic capacitor, improved in recent feeling resistor benefit, a shorted zener diode, a leaky transistor, open circuit or resistor has transformed worth in main aspect can cause ability to blink. As for the secondary facet, a shorted secondary diode, flyback, Incredibly hot, horizontal yoke coil, damper diode, B+ fet, an open filter capacitor, shorted IC and etc can trigger energy to blink as nicely.

Usually what I do is to get rid of the B+ fet initially and link a Light-weight Bulb to distinguish irrespective of whether is the main or after the B+ circuit elements that caused electrical power to blink. Even so in this case, I did not put the Mild Bulb and I directly taken off the B+ fet and power on the observe. For your information, this B+ fet is the N-channel mosfet and this B+ fet is aspect of the boost circuit.

After eradicating the B+ fet, not only the power didn’t blink, there was show as effectively and the anode voltage reads about 12 Kilo volt (a very good keep an eye on must have about 24 KV). The purpose why you received 12 kilo volts is mainly because the increase circuit is not working due to the elimination of the B+ fet. The show proven a small width and the horizontal measurement management is by now set to the optimum (you are not able to get optimum width simply because the anode voltage is only 12 KV). You can manage or set every thing in the On Display screen Display screen (OSD) besides you can’t convey horizontal sizing to greatest.

With owning a display screen, it is a very good clue to me since I understood that numerous circuits is performing these as electricity segment (so you really don’t suspect primary side any more), flyback transformer, yoke coils, micro-p, eeprom, horizontal and vertical circuit, color circuit and even the Osd circuit. Without the need of the B+ fet, there is screen but with B+ fet the electric power blink. In this case, 1 would constantly check the B+ fet first am I right? However the B+ fet turned out to be very good!

Now in which is the culprit hiding? Troubleshooting at times can be extremely frustrated and most of the time is constantly pleasurable. A single of my approaches that I appreciated to use is to contact for any unusually scorching components on board with my finger. (Please just take be aware for all digital repairers-switch off and unplug the electric power cable and discharge the huge filter capacitor in most important side in advance of you commence to contact any components).

Normally just after electricity off, I would contact on the flyback very first then to other components encompassing the large voltage area. When searching the factors with my finger I stumbled on a resin coated ceramic disc capacitor which is pretty very hot. It is located around the flyback transformer and in reality the capacitor was there is to act as a filter capacitor for the 400 vdc line output as shown from the photo.

Soon after the cap was taken out and checked with an analog meter, it showed a shorted studying even in the X1 ohms variety. A great capacitor should really show a cost and discharge activity in the X10 k ohms assortment. A new capacitor substitute for this LG 710E 17″ CRT Keep track of remedied the fault.

The cause why the keep track of electricity blinks is since the defective capacitor grow to be shorted when in total running voltage (improve circuit is working and roughly 60 -70 vdc enter the B+ flyback pin).

When the B+ fet was eliminated (strengthen circuit not doing work and only about 40 vdc enter the B+ pin of flyback) the monitor is not operating under whole operating voltage and the faulty capacitor can even now tolerate (partial quick) and grew to become very hot. I consider if the watch is switched “on” for a small for a longer period, it would trigger the capacitor to build a immediate quick circuit and if this come about, getting rid of the B+ fet to exam the keep track of would not make any various (the power would still blink).