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Old 03-19-2017, 01:44 PM   #1
Yangs
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Default Help converting an old monitor into a lightbox

Hi,

This is my first post here so apologies if this is in the wrong place, or even the wrong forum! Looking around i can tell there is a lot of knowledge here on the subject.

I managed to procure an old monitor from work which I'm trying to convert into a light box for drawing. I've found threads and videos of this being done using a separate power supply to feed the inverter boards, but I'm hoping that i can use the monitors own power supply to do this.

The monitor is an old one with two cfl's.

I've stripped down the monitor to the diffuser layer already and it now functions as a light box, but only for a few seconds at a time. I assume that this a power saving feature, since there is no signal going to the monitor, it turns itself off.

I tried disconnecting the controller board, but the backlight will not turn on without it.

The power supply is a benq 4H L2E02 A35. Does anyone know if there is a trace i can cut/component i can remove/signal i can short to ground, which will isolate the output to the inverters?

All other suggestions welcome, attached is an image of the guts of the monitor in it's current state.

Thanks all in advance!
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File Type: jpg IMG_20170319_191712045.jpg (520.4 KB, 19 views)
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Old 03-19-2017, 02:07 PM   #2
petehall347
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Default Re: Help converting an old monitor into a lightbox

look at the board connectors for one marked bl on
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Old 03-19-2017, 03:11 PM   #3
Yangs
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Default Re: Help converting an old monitor into a lightbox

Hi Pete, thanks for the reply!

I'm looking at the bottom of the power board now and no such luck, the pinout isn't labeled. Would this be on the ten pin cable between the power supply board and the controller? Is there a standard wire colour?
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Old 03-19-2017, 03:21 PM   #4
Yangs
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Default Re: Help converting an old monitor into a lightbox

I found this schematic for a similar (I think) power supply and located the bl on pin.

http://www.eserviceinfo.com/download...BenQ_Q7C4.html

What should I do with it?
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Old 03-19-2017, 03:21 PM   #5
petehall347
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Default Re: Help converting an old monitor into a lightbox

no idea about wire colours .
i think the thing would be to short bl on to 0v gnd using a 1k resistor .
please dont try this without confirmation from someone more knowledgeable

Last edited by petehall347; 03-19-2017 at 03:28 PM..
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Old 03-19-2017, 05:24 PM   #6
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Default Re: Help converting an old monitor into a lightbox

Best thing to do is to provide really good clear straight shot pictures of the top side and the bottom side of the power supply/inverter board so I can trace out the connections.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

Tear down pictures : Hit the ">" Show Albums and stories" on the left side
http://s807.photobucket.com/user/budm/library/

TV Factory reset codes listing:
http://www.badcaps.net/forum/showthread.php?t=24809
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Old 03-19-2017, 07:39 PM   #7
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Default Re: Help converting an old monitor into a lightbox

What model LCD monitor is this? If you can tell us the (bottom-side) BL IC's part number. i.e OZ9938GN or TL1451
Confirm the monitor model number-
I see PSU board has two control signals to satisfy:
CN701 Pin 1 (blk) is "BRT_ADJ"
CN701 Pin 2 (brn) is "BL_ON" or "BRT_ON"

Looks like you need to have two signals right to get it to light up.

P.S. These PSU boards do have capacitor issues, so make sure they are not bloated.
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Old 03-21-2017, 04:32 PM   #8
Yangs
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Default Re: Help converting an old monitor into a lightbox

Hi all,

Sorry for the delay, i didn't get a chance to take clear photos until this evening, i hope that these will help.

_3218860.jpg

_3218862.jpg

The model of monitor escapes me i'm afraid. I stripped this down during my lunchbreak at work, and all the plastics, stand etc, went in the skip when we moved office.

This is the ic on the bottom of the psu board: http://www.datasheetcafe.com/0z9938g...df-controller/

I'll have a dig into the datasheet now, but unfortunately, my electronics knowledge is *ahem* "pre-transistor"

Cheers!

Edit: I can see now that the IC doesn't match the schematic i previously shared, sorry about the red herring!

Last edited by Yangs; 03-21-2017 at 04:35 PM..
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Old 03-21-2017, 04:52 PM   #9
petehall347
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Default Re: Help converting an old monitor into a lightbox

looks like you will need a new set of electrolytic capacitors as they are bulging on top .
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Old 03-21-2017, 09:13 PM   #10
redwire
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Default Re: Help converting an old monitor into a lightbox

I agree - most of the electrolytic caps have a bulged top and need to be replaced first, probably why the monitor was tossed aside. I see a poor solder joint on C709 (near CN701).

I could not find a schematic of the 4H.L2E02.A35 BenQ power supply board. It would be in the LCD monitor service manual. Closest is Russian members-only site: http://monitor.net.ru/forum/benq-ser...anual-205.html
It seems to be used in Q9W5-FP71G+, (not Q7T4-FP71G), Q9T4-FP91G+

The PSU board schematic helps tell us how to spoof the backlight on/off and brightness signals.
I can guess what to do from the OZ9938GN datasheet:
Applying over +2V to "BL_ON" turns on the backlight. I would tie it to +3.3V or +5V.
The DIM pin <0.1V 0% brightness dark panel, 0.2V is min. brightness, >1.5V max. brightness.

BUT you don't what extra electronics is on the PSU board, so this could be wrong.
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Old 03-21-2017, 10:33 PM   #11
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Default Re: Help converting an old monitor into a lightbox

Tracing out the board, it looks like pin 1 (Black wire) is for the Dimming, pin 2 (Brown wire) is the BL-ON.
So to safely turn on the backlights circuit is to use 1K 1/4W resistor between pin 2 and the 5V pin, you will not have the connector connected to the logic board otherwise it will not allow the line to go high.
The dimming control may be PWM not DC control so if he backlights do not come on, then you will have to use another 1K resistor between pin 1 and the 5V, this give max brightness.
But before doing the mod, you will need to replace the caps on the board first.

Last edited by budm; 03-21-2017 at 10:35 PM..
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