AOC Envision L19W861 failure

[mrfixit01]

Being the newbie here, I have looked all over hoping someone else had the same problem I've had. This RadioShack unit worked fine for about 2 years as a closed-circuit tv monitor for a security system. Then one day it just went black. I replaced all the caps (except the largest dog on the field) and all I get is the power light flashing red when I plug it in. Upon hitting power (on board or remote) the red flashes about 6 times and turns a steady blue. The monitor flickers, displays the usual "Please Wait..." and goes black. I have check and rechecked solder joints, wiring, plugs, etc. The unit is 3 years old and is good for nothing but a paper weight right now. Any ideas??? Please?

[retiredcaps]

Originally Posted by mrfixit01

The monitor flickers, displays the usual "Please Wait..." and goes black.

1) If you hookup a working computer displaying your favourite wallpaper, can you see it by shining a flashlight on the lcd?

2) How long does the "please wait" stay on before going to black?

[PlainBill]

What caps did you use as replacements?

PlainBill

[mrfixit01]

Retired Caps:
Thanks for your quick response.
1) With a working pc attached and as bright a flashlight as I could find, there does not appear to be any image on the dark screen.
2) The "Please Wait..." stays on for a mere second.

[mrfixit01]

PlainBill:
Thanks for asking. I bought a kit from LCDalternatives.com which claims "We only sell high quality capacitors manufactured by Panasonic, Nichicon, and Illinois". I can't tell by looking at the caps what brand they are, however. Some are gold/black some are black/silver or white color.

[mrfixit01]

Here's the parts list of those I did replace. (1 ea) 25v-1000uf, 10v-680uf, 25v-470uf, 16v-470uf, 16v-330uf, 50v-22uf.

[jetadm123]

You have two heatsinks opposite each other with a cluster of cap between them. The devices mounted on the heatsinks are diodes that output the 5V and 12V. With your black probe to ground, use your red probe and measure the voltage of the middle leg of each diode and record the voltage.

[retiredcaps]

The inverter transformer is PT801. Report and measure the resistance of the secondaries.

[alexanna]

Is this thing a television?
Wonder if the flashing light is some kind or error code?

[PlainBill]

Alexanna, yes, it's a TV. I can identify RF, Composite, S-Video, Component, HDMI, VGA and audio inputs.

Mrfixit01, there are three possibilities, a failure of the backlight circuitry, a problem with the power supply, or a failure on the signal board. Because of your source of caps I will temporarily ignore the power supply as a possible cause of the problem.

In the upper right corner of the power supply / inverter board is CN202, an 11 pin connector linking the power supply / inverter to the signal board. It appears the pins on the connector are labeled. We'll try this the quick way first. One of the pins turns the inverter on and off, another controls the brightness. The first is commonly labeled BL_ON (or something similar), the second is commonly labeled BRI. I'm interested in the behavior of the BL_ON pin. With the TV off, but (hopefully) connected to a signal source, monitor the voltage on that pin while you turn the TV on. It should start at 0 volts, jump to over 3 volts when the backlights come on, and then may, or may not drop back to 0 volts when the message vanishes. Report the behavior.

IF you are unable to identify the pin I am referring to, either list the labels on the connector or post a picture.

PlainBill

[alexanna]

PlainBill, I Am always learning when I read about things posted in the forum.
Is there a possibility the source of video in may need to be manually selected?

[PlainBill]

Originally Posted by alexanna

PlainBill, I Am always learning when I read about things posted in the forum.
Is there a possibility the source of video in may need to be manually selected?

Yes, but usually a 'No Signal' message would last for longer than 1 second.

My thought processes was that it would be easier to suggest checking the BL_ON line than hooking up a working signal source and stepping through the inputs. After all, some TVs require hitting 'Input', selecting an input, then hitting 'OK'.

PlainBill

[mrfixit01]

Wow Guys!!! Thanks for all the info. I have been at work all day but will print this thread and try to follow up on it tonight or tomorrow. Super Helpful... Oh, it does have a tuner so it can be used as a TV or just a monitor. Presently it is used as a closed circuit surveillance monitor. B

[mrfixit01]

Originally Posted by jetadm123

You have two heatsinks opposite each other with a cluster of cap between them. The devices mounted on the heatsinks are diodes that output the 5V and 12V. With your black probe to ground, use your red probe and measure the voltage of the middle leg of each diode and record the voltage.

jetadm123 I checked the diodes. the one on the left read 13.12v on both legs. the one on the right read 5.0v on both legs with center hot (red).

[mrfixit01]

Originally Posted by PlainBill

Alexanna, yes, it's a TV. I can identify RF, Composite, S-Video, Component, HDMI, VGA and audio inputs.

Mrfixit01, there are three possibilities, a failure of the backlight circuitry, a problem with the power supply, or a failure on the signal board. Because of your source of caps I will temporarily ignore the power supply as a possible cause of the problem.

In the upper right corner of the power supply / inverter board is CN202, an 11 pin connector linking the power supply / inverter to the signal board. It appears the pins on the connector are labeled. We'll try this the quick way first. One of the pins turns the inverter on and off, another controls the brightness. The first is commonly labeled BL_ON (or something similar), the second is commonly labeled BRI. I'm interested in the behavior of the BL_ON pin. With the TV off, but (hopefully) connected to a signal source, monitor the voltage on that pin while you turn the TV on. It should start at 0 volts, jump to over 3 volts when the backlights come on, and then may, or may not drop back to 0 volts when the message vanishes. Report the behavior.

IF you are unable to identify the pin I am referring to, either list the labels on the connector or post a picture.

PlainBill

PlainBill here's what the cn902 labels are on the top right of the PB; (L-to-R) +12v, +12v, G, G, +5v, +5v, +5v, G, G, N/F, Dim.
reading the +12v pins: 13.08v, the +5v pins: 4.96v, N/F fluctuated between around 200 & 400 mv off and jumped to 3.96v on. Dim read 2.6v on but varied between 4.0v & 28mv off. Turning pwr on then off Dim went from 28mv to 2.6v, jumped to 3.4v & dropped quickly back to 2.6v and steadied there until pwr off then back to about 28mv. Hope this helps. Thanks.

[mrfixit01]

Originally Posted by alexanna

Is this thing a television?
Wonder if the flashing light is some kind or error code?

According to their manual it is a sort of power on test. Normal action. Thanks.

[PlainBill]

Originally Posted by mrfixit01

PlainBill here's what the cn902 labels are on the top right of the PB; (L-to-R) +12v, +12v, G, G, +5v, +5v, +5v, G, G, N/F, Dim.
reading the +12v pins: 13.08v, the +5v pins: 4.96v, N/F fluctuated between around 200 & 400 mv off and jumped to 3.96v on. Dim read 2.6v on but varied between 4.0v & 28mv off. Turning pwr on then off Dim went from 28mv to 2.6v, jumped to 3.4v & dropped quickly back to 2.6v and steadied there until pwr off then back to about 28mv. Hope this helps. Thanks.

This appears to be a case of 'two seconds to black'. You can verify this by hooking up a source with audio and video, stepping through the inputs, and verifying that sound remains after the backlights go away. You test verified that the backlights are shutting down, they are not being shut down by the signal card.

Possible causes include bad caps, bad CCFLs or the wiring to them, a bad inverter transformer, or a bad component in the inverter protection circuitry. I see several possible approaches. The easiest appears to be a very rudimentary CCFL test. Disconnect all but one CCFL. Turn on the power. Do you get a display on the screen (it will be dimmer than normal)? Turn off the power, disconnect that CCFL and connect the next one. Turn on power. Repeat for the remaining CCFLs. If one CCFL does not produce light, that CCFL or the wiring for it is bad. If all light to the same brightness, I'd pull the power supply / inverter board and look for any signs of problems on the back side. If nothing shows up, replace all the electrolytic caps on the power supply / inverter (with the possible exception of the large electrolytic).

If you have another monitor with 4 good CCFLs with compatible connectors, try hooking up all four. If they stay on, the problem is the CCFLs in this monitor.

PlainBill

[mrfixit01]

Originally Posted by PlainBill

This appears to be a case of 'two seconds to black'. You can verify this by hooking up a source with audio and video, stepping through the inputs, and verifying that sound remains after the backlights go away. You test verified that the backlights are shutting down, they are not being shut down by the signal card.

Possible causes include bad caps, bad CCFLs or the wiring to them, a bad inverter transformer, or a bad component in the inverter protection circuitry. I see several possible approaches. The easiest appears to be a very rudimentary CCFL test. Disconnect all but one CCFL. Turn on the power. Do you get a display on the screen (it will be dimmer than normal)? Turn off the power, disconnect that CCFL and connect the next one. Turn on power. Repeat for the remaining CCFLs. If one CCFL does not produce light, that CCFL or the wiring for it is bad. If all light to the same brightness, I'd pull the power supply / inverter board and look for any signs of problems on the back side. If nothing shows up, replace all the electrolytic caps on the power supply / inverter (with the possible exception of the large electrolytic).

If you have another monitor with 4 good CCFLs with compatible connectors, try hooking up all four. If they stay on, the problem is the CCFLs in this monitor.

PlainBill

I guess by CCFL you mean the 4 plugs that go to the back lights. (I'm a real newbie, now.) I tried unplugging all the wires and plugging them in one at a time. The same thing happened as before, just dimmer. I already replaced all the PSB e-caps except the large one. I have looked at the back of the boards twice now and don't see anything abnormal. Thanks for all the help so far. Check back later.

[mrfixit01]

So, I guess no one has any additional ideas on the AOC Envision 19"? I'm open to any more ideas. I've already tried everything everyone has suggested. Please?

[retiredcaps]

Originally Posted by mrfixit01

I've already tried everything everyone has suggested. Please?

Post #8? What did you get for ohms measurements on the inverter secondary transformers?