Re: KDS LCD monitor, Sampo Inverter..

Jamie <jamie_ka1lpa_not_valid_after_ka1lpa_@xxxxxxxxxxx> wrote in
news:P25jl.37$Qn1.8@xxxxxxxxxxxx:

Arfa Daily wrote:
"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@xxxxxxxxxxx> wrote in
message news:rhMil.12694$Yz.3378@xxxxxxxxxxxxxxx

Franc Zabkar wrote:


On Wed, 04 Feb 2009 22:30:57 -0500, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@xxxxxxxxxxx> put finger to
keyboard and composed:



It appears I have a failing inverter with a KDS 17" monitor.
this is a dual unit Sampo QPWBGL9151DG
http://www.lcdpart.com/Products/qpwbgl9151dg.html


I found a pin out on the net and states that pin's
1,2 = 12V, it has that, pin's 3 is a On/Off, it's at
~ 4.1 volts via a resistor from the processor board coming from
a 5 volt source. Pin 4 is a dimmer control, it's at 3.35 volts,
5 is ground/common..

With that, I assume the inverter board should be operating and
generating some voltage to the CCL lamps?

Is my assumption correct? If So, I guess I need to repair the
inverter ?


It could be that the ON signal is active low, in which case shorting
it to ground should turn on the inverter. To find out for certain,
you may find an application circuit in the datasheet for the main IC
(top centre in your photo). It may also be helpful to view the data
for the 8-pin ICs below each of the coils.

The usual culprits in inverters appear to be electrolytic
capacitors, so I'd change those first. I'd also reflow the solder
joints at the transformers and coils.

- Franc Zabkar

Ok, i've already tried pulling that On/off signal to ground.
It does nothing, Normally standard markings of on/off is the same
order as +/-, since I'm getting + to that pin from the processor
board via a resistor from a 5 volt supply, I guess that thought is
out the door, but like I said, I did pull it low with out success.

There is 1 electrolytic on that board that seems to be related to
both
inverters . I will lift the board from the chassis and inspect
closer..

thanks.


I'm pretty sure that I can see two electros on there - one
conventional through-hole, and one s.m. Have you looked carefully
for a s.m. fuse ? They usually have one soon after the incoming
supply, and it is not at all uncommon for them to fail for no good
reason. Have you followed print from the on / off control input to
see if you can find a transistor that does the actual switching ?

Arfa


Actually, I made a mistake on the vender of the monitor, it's AOC, not
a KDS, I don't know where my head was at on that one.

Any ways, last night I got back into it, yes, the large cap in the
view was defective. Spec'ed out to be a 50uf 30v, tested as 1.2 uf.

So, I replaced it with what I had close to it at the time, 47uf, 35V

Still does not fire up how ever, I'm not sure as to what the
"On" signal voltage is suppose to be? Currently I have 4.18 volts
when
unit is switched on at the control pin. Since this unit operates
from
a 12 volt level, I'm making assumptions that I'll need to insert a
video signal and see if this level turns into like 12 volts of so..

At this point, I just assumed the inverter should kick in with no
video signal and at least show something for a short time like a
"No signal" or Menus before it goes to sleep.

Tonight, I am charging up one of my older laptops to be used as a
video signal to give this a try...

I may have it fixed, Just may not have one of those monitors that
shows anything at all unless I active it out of sleep mode with a
video signal (yellow light)..

P.S.
I didn't want to override the on signal with something higher than
that in fear of unneeded additional damaged.

It sure would be nice if I had a service manual for this to so me
the
prints.. To me, this is just a shot in the dark project to see if I
can save this monitor and use it for a spare.. It's not worth it to
me to
sink lots of money into when you can buy them so cheap these days.


http://webpages.charter.net/jamie_5";



I have often found that the small value ceramic capacitor across the
inverter coil causes backlight failure, so you might try replacing it.
.

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