Black LG L1952T-Sf Sceeen Test

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Two Questions;

The source tells me it has just died. "the fuse" must have blown was
their comment. After me giving it a quick look over they decided to just
go buy a new replacement, I thought I'd have a play with it.

Tried all the obvious, aka they might have pressed the wrong button type
tests but applying power brings no lights/leds and thus no response.
There is a 'DVI-D' inlet, but with no power light showing,
i couldn't see the point of sourcing a cable and a system with the
appropriate video card to test if it was just and inlet socket problem.

Been to the lge site and no directly appropriate manual, so before I go
to step two(trashing it), I thought I'd ask if there are any other tests/
tricks to try on these.


Q2; how do you take them apart with the minimum damage?
Removed the four screws on the back(only ones visible and no effect.
Started to lever the screen surround off with a flat blade, but that was
leaving marks no matter how careful. So, I'd thought I'd ask here. if
that was the way to go and phutt to the marks/scraps?

TIA.

 

Re: Black LG L1952T-Sf Sceeen Test



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Nah, use plastic strips, I use that insulation plastic found in power
supplies under the PCBs.  Cut up into some 1.5cm x 8cm lengths, force
a corner into the joint, bend the plastic over and get the other end
in, the add a couple or more strips until you can pop a case latch.  

Repeat around edge.  Take your time, it's much quicker after the first
couple monitors :)

Trying different places to start might help, once you feel where the
latch tabs are, it's easier.

Grant.
--
http://bugs.id.au /

Re: Black LG L1952T-Sf Sceeen Test



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Thank you, very helpful. will keep it in mind for next time.


I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test



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After searching the Lge sites and not seeing this monitor listed in
discontinued (suspect very old), i decided to just disassemble it anyway.
Removed the four screws, then levered the screen surround off breaking
every plastic latch, four per side.

Then the innards would come out.
Sheesh, all held together by tape, except for the clip on cover for the
screen power cables, which obviously provided a shield path for the
screen itself back to the cage containing the power supply and driver
boards.

No burnt out track or obviously damaged components on either board, so
I'm wondering if I could play with bits a bit more?

Q. what voltages would the power supply being supplying directly to the
screen? Just labelled high voltage on the sockets.

I assume these drive the backlit lamps?

Found a pdf that says 5V, 0.745ma normal, 3A max inrush?
Does this sound correct?
There was nothing specific about lamp supply power .


Q. How do a I drive the DIM & M/S pins?
There is an 11 wire jumper from PS to I/O board, pins labelled as follow;
# PS(IO)
1.  12V
2.  12V
3.  GND
4.  GND
5.  5V
6.  5V
7.  GND
8.  NC <- not connected
9.  ON (INVON) <- signal to PS to turn off and on?
10.  DIM (DIMADJ) -0-5V?
11. M/S (LAMPADJ)

TIA

Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test


On Sat, 24 Apr 2010 05:10:06 +0000 (UTC), terryc

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Can happen first time.  You DO get better at it after a few.

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You want permission?  Goferit.  But play safe.

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600-700 typically on those I've bothered to test.  Will ddeefinitely
get your attention if you make contact.

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Yup.  The other board (video) provides the signal info to the screen.

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Pass.


Bet the manual IS out there, but I don't have the energy right now to
chase it.  It's not essential.  Start with some basic fault-finding
which doesn't need a manual, but does need some care.

Before testing though, have a close look all over the boards - both
sides.  (A good Mk1 eyeball can preempt a LOT of measuring and circuit
examination.)  You are looking for:

.  bulging/leaking electros on the PSU board.
.  any signs of charring or excessive heatingon the non-copper side of
the PSU board.
.  any semis with damaged flat surfaces.

If nothing found, ...

With everything plugged together and AC applied, turn on with front
panel switch (assuming there is one).  Check for voltage ~340DC on the
large cap on the PSU board.

If it is there, the fuse and rectifier bridge are working.  Next,
meter the labelled 5V and 12V points vs chassis ground.  If OK, the
switcher is running OK.

"Normally" the PSU board drives the backlighting in response to two
control lines from the video board - an analog brightness line ("DIM")
and an on/off function ("BL_EN") which is *generally* a 0/5V logic
signal.  If the above tests return OK, I often release the BL_EN out
of the connector and force it to verify that the backlight system
functions properly.  The BL protection circuitry (on the PSU board) is
not disabled by this step, but I don't persist for more than a couple
of secs on this.

Hope this isn't a case of teaching my grandmother how to suck eggs.

Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test




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Nope, these are all new to me. Very helpful info there. thanks

I've fiddled with monitors in the past, basic fixing, but mostly it was
case of just keeping the best, plus looked closely at laptop bits (no
doco).

The fact that these are basically three modular bits, (LCD, PS & IO/
driver) encourages me to fiddle more.


Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test


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Did a few Samsung ones recently - it was faulty electrolytics in all
cases.
Another had the added bonus of a blown fuse in the 18V line to the HT
(lamp) EHT supply section.

Don't know why it blew, but when replaced with the correct value has
worked without a problem for the last month.


Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test


On Sun, 25 Apr 2010 00:51:44 -0700 (PDT), kreed

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My experiences with LCD monitor repairs have been similarly routine
with the exception of Samsungs.  I have several here where the micro
(NT68F63L) appears to have decided that good signals are nonexistent.

Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test



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Fixed a Samsung 943BW LCD Monitor this morning.
3 bulging capacitors in the power supply.
Must have been a heap of these capacitors around in monitors like
this.
Pretty easy to do , so a cheap fix if you arnt put off by pulling
things apart.


Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test



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I'm not put off by opening the case, although on most LCD's to date it
IS the most time-consuming part of repairing them.

Done lots, it's just these f#$@#$ Samsungs with the intractable micro
issue that are bugging me right now.  And (of course) the data sheet
for the micro is nonexistent, so I can't even check the sense behind
the widely-mooted "stick a 50R across pins 5 & 6" kluge.

Re: I've disassembled it. Re: Black LG L1952T-Sf Sceeen Test


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Sounds Identical to the problem we have been having.
We have over 30 of these 17 & 19", and 5 failed within 2 months.

One other we opened, had a newer model power supply in it, caps looked
the same as the bad ones
but were ok. Replaced them anyway.

Compared to the cost of replacing 30 monitors, this fix is a bargain.

Watch out for that fuse too (looks like a resistor) that takes the 13v
to the screen inverter circuit.

Re: Black LG L1952T-Sf Sceeen Test


On Sat, 24 Apr 2010 03:12:20 +0000 (UTC), terryc

Google suggests that the chassis number is LM57B.

Here is a service manual for MODEL: L1953H (L1953H-BFQ.A**MQP),
chassis LM57B:
http://radiomen.ucoz.ru/L1953H-SFQ.A..MQPS.pdf

Here is a user manual for L1752T L1952T L1752TX L1952TX L1752TQ
L1952TQ L1752TR L1952TR:
http://pdfs.icecat.biz/pdf/1882512-9548.pdf
http://www.tecno.cl/archivos/0802LGG019_ing.pdf

See pages 30 & 31 of the service manual.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

Re: Black LG L1952T-Sf Sceeen Test




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Thank you for all those. most helpful.
I have enormous trouble finding anything seful like that in service
manuals online. Too many shonk sites.

Re: Black LG L1952T-Sf Sceeen Test


On Mon, 26 Apr 2010 14:46:29 +0000 (UTC), terryc

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Try filtering your Google hits:
http://www.google.com/search?q=%22L1952T%22+filetype%3Apdf+OR+filetype%3Adoc+%22manual%22+OR+%22guide%22+OR+%22instructions%22

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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