benq fp91g+ (q9t4) monitor not turn on

[paulmars]

benq fp91g+ (q9t4) monitor. Mostly wont turn on. Once in awhile it does
and works fine. However, that's very seldom. The on off switch hot side
is 3.3vdc. The switch grounds that when its pressed and my dvm then
reads 0vdc. Every time. Ive traced it to the display circuit board
plug, gray wire. So, it goes from 3.3vdc to 0vdc when the switch is
pressed - Every time. Over and over I can do this and every once in
awhile, the unit powers up and it works fine. however, the next time,
it wont power up.

Any ideas what could be wrong? All the caps look fine. Ive also
inspected all solder joints.

tks,
pa

 

[Harvey]

The switch works the same as the start switch on a motherboard. It grounds a logic pin that then turns on the power. It sounds like something in the logic circuit is intermittant and failing.

The problem may be as simple as finding a faulty resistor, capacitor or diode, or it may be in any part of the logic/control circuitry, which, in turn may be a small part of a large integrated function block. You would need a schematic and diagnostic info to chase it down. The problem could also be caused by noise spikes or low voltage on some part of the power supply.

If you don't have the required tools and documentation, a qualified tech may be able to repair it. Then, you'd have to determine whether the cost of the repair, including technical labor time, is worth the current value of the monitor in working condition.

The sad part about modern microelectronic integration is that it's no longer possible to locate a single logic part in a socket (when they bother with sockets), let alone replace it. We live in an age of disposable large electronic systems where it's cheaper to replace them than to repair them.

 

[LongTimePCUser]

A few years ago there were a lot of capacitor failures in Samsung and other monitors and TVs.
The problem was capacitors that they bought from Chinese suppliers that would fail after 1 - 3 years.

This is a well known problem.
You can get a repair kit for your montior here:
http://lcdalternatives.com/Repair-K...itors-Only-Not-the-Entire-Board-P2502271.aspx

They also have video instructions on how to do the repair at this site.

 

[paulmars]

tks. I need to decide if im gunna try the caps, since they all look good.