On Fri, 7 Feb 2014, 2phar wrote:

On 2/7/2014 8:57 PM, Phil Allison wrote:
"2phar"

I have a BENQ G2420HD 24" LCD monitor.

Display backlight seems good, etc. But unit shuts down completely after
about 20-30 mins (no backlight, power LED goes out). Holding down power
switch at this point will cause unit to come back up after about 30-40
seconds. Then it will die again within 5-10 mins, but can be restarted the
same way.

I've already replaced all the elect caps on the power supply board.

Is the power board still the most likely problem here? Any suggestions as
to how to pinpoint the cause would be most welcome.


** The fault condition is being brought on by rising temperature - right ?

So you need to apply heat ( ie hot air) SELECTIVELY to various parts of
the
PSU until you find the area that is most sensitive. This could take quite a
while.

I have an amplifier module ( from an ART 322A) here that reacted to the
application of hot air by going silent. The cause was a number of cracked
vias ( plated through holes) in the PCB going open when the board became
warm.

The particular vias are about 0.25mm dia and not filled with solder.

Unusual fault and a nightmare to find and fix.


... Phil





Yes.. it sure seems like it's heat related. I redid the compound on the
heatsinks and stuff, and nothign seems extraordinarily hot when it shuts
down. I have gone and got an IR thermometer as N_Cook suggested, so I'm
gonna see if I can track it down.

I'm curious as to why its possible to get it to restart within 40 seconds and
it keeps going for several minutes again, if it was due to some thermal
expansion or thermal shutdown, that does seem kind too fast a recovery?

I also wonder if it could be a fault elsewhere like in the inverter board
that's able to cause the whole power supply to shut down?


Only if it's causing a load on the actual power supply which cause the PS
to shut down.

Are you sure you got all the capacitors?

I dragged a 19" Acer monitor home, and it worked fine, or so it seemed.
But if I left it on, it would go into standby and then I couldn't get it
activated again, the Acer logo would go on and nothing more. I changed
the obvious capacitors and it's fine. So it was resetting because one of
those bigger electrolytics in the power supply wasn't quite right. I
nitially thought it was something else, but changed the capacitors because
it was easy.

Michael