Re: LCD Monitor Problem - Turns on and off


"tvguy" <no@xxxxxxxxxxxx> wrote in message
news:TvOOf.7298$Pu3.1234@xxxxxxxxxxxxxxxxxxxxxxxxx
Arfa Dailywrote:
"tvguy" <no@xxxxxxxxxxxx> wrote in message
news:1A6Of.198994$H54.155366@xxxxxxxxxxxxxxxxxxxxxxxxx
It don`t sound like a bad inverter if it is running good when
plugged
directly to the wall outlet. If it only does this when plugged into
the powersupply of the computer then this would be a problem of the
computers powersupply. Did you try to plug it into another computer
to see if you still have the same problem ? I would suggest to try
this first and see what happens.


Maybe I read it wrong, but I don't think that this is what the guy
was
saying. I read it as he was always using the external power unit, that
came
with the LCD monitor, and if he left it plugged in the wall, ie with
power
always available to this power supply, but with the monitor turned
off, when
he came to switch the monitor on, it came on ok. If, however, he
plugged in
to any power source that was turned off for periods of time eg his
UPS, or
unplugged from the wall for any length of time, then when he came to
put
power back on the PSU, and then tried immediately to switch on the
monitor,
he got the buzzing, spitting failure to start up, which is typical of
a
defective switching PSU, with bad electrolytics. Perhaps the OP can
confirm
??

If this is actually the case, then all the stuff about Windows and
rebooting
etc is probably a red herring. It just relates to the length of time
all
this takes, which gives the power supply time to struggle to a
startup.

Arfa[/quote:733e2a47e2]

If that was what he was stating. I may have read his post wrong to
what he was trying to say. Then I would have to say yes that he has
something wrong with the external powersupply.


Yeah, I think that's what he's saying, tvguy - see his additional post
above.

Bill.

I think me and tvguy are now both in agreement. Yes, go for power supply
trouble. I had a FAX machine on my bench last week, which was powered from
an external 24v 1500mA switch mode supply. If left on, it would work for
ever. However, if left unpowered for a few hours, when put back on, the
power supply would struggle for about a minute, to start up.

Once I got inside it, it was fairly obvious that the two series-connected
82k startup resistors were pretty distressed and high. I replaced both these
( they use two in series to double the voltage rating of these small film
resistors ). Also, there was a single 220uF cap on the primary side. When
checked on my ESR meter, this went 38 ohms, which is way, way too high, so
this item was replaced as well. The supply then started up first time, every
time, no matter how long it had been off. Both of the mentioned components
are very common for causing startup trouble in any switcher.

Just a word of warning. If you are not used to switchers, be very very
mindful of your personal safety. This type of supply is VERY dangerous, and
could be lethal. Remember also, that the main smoothing cap will charge to
almost one and a half times your local input voltage. If the supply doesn't
start up, this cap will likely stay charged to very close on this figure for
hours, as most switchers do not employ a leak resistor across it. I would
always recommend having these supplies connected to a bench isolation
transformer, when they are opened to be worked on.

Arfa


.

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