BenQ LED G2420HDBL Monitor Repair.
The BenQ monitor in my workshop that i use for testing VGA and DVI outputs stopped working. Initial symptoms were, turn the monitor on and after 5 seconds it would turn off again even though displaying an image briefly. Repeating power up gave the same problem until eventually it wouldn’t power up at all.
So i decided to take it apart and fix it and do a blog on the repair at the same time.
All information contained on these pages are here for my reference only, i will not be held responsible for any damage or injury done to you or your equipment ! Some parts of electronic equipment can hold high voltages which can shock or burn, some electronic components are very susceptible to static discharge. Aging IC’s and pcb tracks can be easily damaged if due care is not used when working on them…
You have been warned !
The service manual for this model can be found online here in downloadable pdf format, and the relevent schematics required are on pages 60-68
The chassis could now be lifted clear from the screen, and the screen put somewhere safe..
With just the chassis on the bench i turn my attention to the power supply pcb, its held on with 4 screws (Arrowed) so i undo and remove these, one of them has a ribbed washer as its an earth screw, so i made note of its position, so it can be refitted in the same place.
Next i turned my attention to the IC with the blown leg IC601 , its a TOP258PN an intelligent power switch which incorporates a power MOSFET, PWM control, oscillator, thermal shutdown circuit, with over and under voltage protection all in one small DIL package.
For those 2 components to be damaged the large 68uf 450v power filter capacitor at C605, can’t of been doing its job properly, so i decided to change this capacitor and whilst i was at it replace all the radial electrolytic capacitors on the power supply pcb. Mass produced Taiwanese monitors have a tendancy to be fitted with cheap sub standard capacitors, so it pays to replace all electrolytics whilst the pcb is out.
68uf 450v 105°
470uf 35v 105°
330uf 50v 105°
680uf 25v 105°
47uf 63v 105°
10uf 63v 105°
A The temperature rating, usually 85° or 105°
B The farad rating (capacitance value)
C The operating voltage
The trick here is to match the farad rating and the temperature rating, with the voltage rating you can either match or better still go for a higher voltage rating, still bearing in mind the physical size of the capacitor, it still needs to fit in its place on the pcb.
As these are being used in the power supply section, my replacements are still 105° and my capacitance values are the same, but i’ve gone with slightly higher voltage on all the capacitors except the main 68uf filter cap which is still rated at 450v.
Another thing to be wary of, is make of capacitor, there are a lot of cheap capacitors around for sale and also alot of FAKE capacitors. Try to buy well known japanese makes from reputable companies. I use Panasonic, Nichicon, Rubycon, Sanyo/Suncon etc...
Soldering whether for removal or installing of components can be an issue, depending on the kind of pcb track the solder pad is in or is connected to. Some are fine small pads, but some have larger surface area, and these require more heat. If your soldering iron starts to stick to the pad your soldering then its not hot enough and is struggling to keep up with the heat dissipation. I use a Metcal intelligent soldering station, with twin irons. On one i have a 0.75mm conical tip installed for fine work and on the other iron a 3mm chisel tip for when i need that extra heat.
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Kernowtronic and are Copyright © 2016
They may not be copied or used without prior permission !