AOC Envision 32 inch L32W761 no picture or sound

[Bilbo]

Hey all, I have a friends AOC Envision 32 inch lcd model L32W761 which has no picture or sound. It has a yellow led light when off, which turns green when turned on (makes no sounds when turned on), when turned back of led light blinks yellow 17 times then goes steady yellow. No visual bad caps or damage to boards. I'm still little new to fixing TVs and, not that great at reading their diagrams yet, but I always like learning. Got lucky and fixed a 52 inch RCA projection, a sanyo 42 inch lcd and a dell 27 inch. Here is a link to a service manual I found. The cover page says it's for a 26 inch but the diagrams are for a 32 inch as well (as indicated on lower right of diagrams) and are the same boards as the one I'm trying to fix.



Power supply board pn 715T2463-4, mainboard pn 715T2486-2
Currently I have no 24 vdc to the inverter board from the power supply. All fuses checked good. With the tv power off (at cn902 power from Psu to mainboard),(pins 1 & 2 not used on this model) it has 13.52 at pins 3 & 4, 5.29 vdc at pins 5 & 6, good grounds at pins 7 - 8, 0 vdc on pin 10, 0.03 vdc on pin 11, and 0 vdc at pin 12. (Note all volts are the same for corresponding pins for cn901 at mainboard power off and on) At cn903 (Psu to inverter) it has 2.92 vdc at pin 12 on/off, 3.31 vdc at pin 11 dim, good ground at pins 10 - 6, no 24 vdc at pins 5 - 1.
I disconnected the inverter and tried the lamp load test with no results. I picked up some spare parts from another tv (power supply, mainboard, inverter, t-con) which were untested, broken screen. Slaved them in with no change. Used power supply or main may have the same fault/problem. Wondering if if it's a power switching problem or stuck in stand by.
Any help will be greatly appreciated. Thanks

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Forgot to mention I tried the hair dryer and freeze spay with no luck.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Correction
Currently I have no 24 vdc to the inverter board from the power supply. All fuses checked good.
With the tv power off (at cn902 power from Psu to mainboard),(pins 1 & 2 not used on this model) it has 13.52 at pins 3 & 4, 5.29 vdc at pins 5 & 6, good grounds at pins 7 - 8, 0 vdc on pin 10, 0.03 vdc on pin 11, and 0 vdc at pin 12. (Note all volts are the same for corresponding pins for cn901 at mainboard power off and on)

With power on (steady green led light) cn902 has 13.11 vdc at pins 3 & 4, 5.30 vdc at pins 5 & 6, 2.92 vdc at pin 10 on/off, 1.87 vdc at pin 11, and 3.31 vdc at pin 12 dim. At cn903 (Psu to inverter) it has 2.92 vdc at pin 12 on/off, 3.31 vdc at pin 11 dim, good ground at pins 10 - 6, no 24 vdc at pins 5 - 1.
Sorry for no putting all the info in 1st post, was a little tired last niqht, and it wouldn't let me edit it this morning.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Here's some pictures off the power and main boards

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Here's the power board top

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Here's the power board bottom

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Here's the main board top

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Here's the main board bottom




By the way, sorry for putting picture on five different post, but seems like they are too large for one post. Anyway I've ordered an ESR tester and will check caps more when it arrives. Any suggestions in the mean time?

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Ok, after restudying the diagrams, I noticed pin 11 at cn902 on power board is for ps on, which only has 1.87 vdc with power switch on and steady green led on light. With power switch off, at power board top side below cn902 (middle right side of pg 48 in manual) I'm getting 5.3 vdc (coming from +5v source) going into and out of r974, 5.3 at pin 1 and 4.5 at pin 2 on ic904. With power switch on I get 5.33 in and 1.21 out of r974, 1.21 at pin 1 and .07 at pin 2 on ic904. So I de-pinned pin 1 at cn903 on main board (wire coming from pin 11 cn902 on power board) (left upper on pg 47 of manual) and rechecked voltages. With power switch off and on I'm reading the same volts as stated above for power switch off. But, with wire disconnected, there is 3.27 at pin 1 cn903 on main board. Seems like something is drawing the volts down when wire is connected and not turning on power supply. I desoldered one end of r974 and received 991 ohms (both directions). Diagram states 1k 1/4w for r974. Note: r974 checks the same for original and spare power board, both seem to have the same issue.
Any ideas, should I start checking components on bottom of power board or ones on main board? Note: I'm still have not received my ordered esr meter.

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

OK, we need to know if the PS_ON signal is working not by checking the DC voltage right at the two legs of the 450VDC main filter cap when TV is off and when it is turn on.
It should have about 170VDC when TV is OFF and about 370~400VDC when TV is ON.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Thanks for the reply budm, I'll slave the power board back in and give ya a reply shortly

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Sorry for the slow response (Friday night, hehe), anyway at c973 with power off I'm getting 167vdc off both legs, and 402vdc with power on.

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

OK, the PS_ON is fine, when PS_ON is applied, the PFC Voltage booster will kick up the voltage for the 24V power supply to run on. So we need to look at the 24V power supply section next. There may be a fusible fuse that the 402VDC is fed into to feed to 24V power supply section.
Since we do not have the schematic diagram for this power supply, it will be a matter of tracing out the traces on the bottom side of the board to see how it works.

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

The SMPS IC902 and the MOSFET Q902 are for the 24V circuit. Try to get the P/N as printed on top of the IC so we can get the spec sheet for it.
Check the fusible resistor R976.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

I thought the power supply diagram was on page 48 of the manual, link on 1st post, or to ya mean for individual part numbers?
I'll look at parts list and on power board for part numbers, thanks

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

Sorry, I just down load the service manual just now.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Np, thanks for all the help. Hate to trash my friends tv, and would be nice to check out the other spare parts I have. Never know when someone can use them or I could always sell them if functional.

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

So check that fusible resistor R976 to see if it is open.

[Bilbo]

Re: AOC Envision 32 inch L32W761 no picture or sound

Sorry, I'm still a little new at some of this, learning as I go, can ya explain please. Do I need to unsolder to check it?

[budm]

Re: AOC Envision 32 inch L32W761 no picture or sound

TV unplug, then just check the resistance of that resistor R976, it should show about the same resistance reading as when you touch the two probes of the meter together.