The REAL Problem
by rclaunch - 7/19/05 8:40 AM
In Reply to: The Power Supply Fix by dthomasix
I was unaware of the HP monitor probelm until today. After reviewing the posts in this forum I thought I would add my 2 cents.
The root problem appear to be the high voltage backlight inductors. The users need to understand "HOW THINGS WORK"! The LCD panel displays the image but the image cannot be seen unless the back light panel provides illumination from the rear of the LCD panel (simplified explanation). The back light controller unit takes the low voltage of the power supply (12 volts?) and increases it through the inductors to a much higher voltage (100+) and a higher frequency (60-400Hz). As a result these parts get HOT!.
The backlight of an LCD monitor is ON all the time, even when your screen saver is activated. Only when the monitor is in STANDBY or OFF is the back light shut off. A bouncing Windows XP logo as your screen saver appears on a black background. What you may not realize is that the black portion of the screen is not the result of a turned off backlight, but instead is the result of polarized liquid crystal elements PREVENTING the backlight from being seen by you!
Screen savers look pretty, but are useless for LCD monitors. Screen savers were designed to prevent TUBE-based monitors from burning images on the screen. LCDs are completely different. They operate on the principal of crystal elements polarizing light. This light comes mainly from the back light panel. If you see something on an LCD screen, it means the backlight is ON.
Backlight panels do have a limited life. Anywhere from 40,000 to 100,000 hours. You could leave your monitor on for about 5 years and just begin to exceed the 40,000 hour figure. As a rule, I use a large UPS and NEVER turn off either the computer or the monitor. I use the screen saver just as an indicator that the PC is on. The monitors on my system (NEC 21") are 8 years old and still look factory fresh.
The posts on opening the monitors and resoldering the legs of the inductors sounds like the solution. It would appear that either the manufacturing process did not wet enough solder on these legs, OR the circuit board was improperly designed and the solder pads of the board are not large enough. Over time the legs of these parts go through cycles of hot and cold causing the solder joints to crack.
A word to those who have received replacment monitors: If the problem is the size of the solder pads on the back light board, get ready for a repeat in 10-14 months.
For all you budding technicians: be careful when you solder the inductor legs not to flow solder across the joints. The inductors will cause a spectacularly catastrophic failure if they are shorted and power is applied. Always put the monitor BACK TOGETHER BEFORE POWERING ON!!
For those purchasing new power packs: yes it will help, but only for so long. The additional voltage and current allow the unit to bridge the solder cracks, but eventually they will get wide enough to stop working.
For those messing with drivers and screen savers: if the monitor shuts off when booted to DOS or you PC's setup screen, leave your Windows setup alone! Check the monitor on another computer, you won't hurt the computer.
I am sure that some of the problems users have had were in fact incompatible drivers, bad power packs, bad cables and so on. BUT there does appear to be a distinct design/manufacturing flaw in the HP LCD. They do need to step up to the plate and take care of their #1 source of revenue, THE CUSTOMER.
25 years of electronic circuit and system design, including LCD monitors and touch screen!
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