Re: fixing a Levono/IBM 6659 PCD monitor (any idea what part 'F701' might be?)

Sorry, if did not see your second reply when i first reply.
You said on the second reply, that it needs a restart after 15 min.
I see a whole bunch benq 's lcd has the same problem, sometimes it is
the transistor, or capacitor, transformer, or even cold solder joint.

If you have an ESR meter, you can check the capacitor(disacharge the
big cap before mesauring it)
Colder solder joint is easy to find, just need to look carefully.
Transformer(inverter) is liitle bit difficult, Since it is difficult to
find the replacement

First i will look at the board, and see any discoloration(if something
run hot for a long time, it will change the color of the board.) If
somthing run very hot, it usually break first.
Then Measure the cap with esr meter,check colder joint, then measure
the voltage of different rail, and find out which section cause the
problem.

Usually the manfacturers don't give out any service manual, but if you
want to learn how lcd
power supply works, you can goolge "hp vf17 manual". This is a service
manual for HPvf17, it has the block diagram and flow chart. It teachs
you a lot so read it carefully and try to understand it as much as
possible.


i guess your lcd may has bad caps or colder solder joint, since you
can't power it up 50%of the time and it needs a restart will made the
lcd alive again.



grindlay@xxxxxxxxx wrote:
Right I see. Well, repairing smpsus driving EHT stages is not
especially straightforward, so if youre a graduate student I dont think
your odds are very high on this.

Just out of curiosity, are there typically EHT stages in LCD monitors?
Maybe for the backlight?


However if you must, the smpsu is refusing to start: why? Either its at
fault or its going into protection mode because of a fault downline,
which usually means a horizontal output area fault.


A bit more info on the symptoms which might serve as a clue: For about
10 minutes after the DC powersupply is plugged in to the monitor, the
unit will power up fine. However, after it has sat for 15 or 20
minutes plugged-in, it will then refuse to power up until its unplugged
and then re-plugged in. The powerswitch is just a SPST button (checks
out fine) that pulls a logic signal low. That's about all I could get
from probing the (multi-layer) board. Strange symptoms, but I'm hoping
useful info for someone more experienced than me.

thanks,
Graham

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