STV-668-UHD-55BK Devanti TV not turning on

[phred01]

G'day all
Wish to fix this TV. No help from Devanti they have no service department & no spares Their attitude return to purchase point if within warranty period else stiff $hit buy another TV. Determined that Power board was faulty as the audio opto o/p was not glowing. Finally was able to track down a new power board. The audio Opto now glows so the main logic board now has power But the power on light is not glowing so the power up cct has a fault. The power input is 12v, pwm led tcon signal & PS_ON  2 signal lines for power up the TV. The PS_ON fluctuates between 1.8v and 0v obviously this is stopping the TV from powering up. Used a meter to locate one of two on board smps that reduces the 12v to 3.3v or 5v. Suspect that the local smps that powers the remote receiver is the problem. BTW the manual power on button doesn't turns on the TV either. The SMPS chip marking is 01=P1Z but cannot find any data. So far cannot find a replacement logic board nor locate a manufacturer Please find attached relevant pictures Cannot believe the TV is an orphan solely made for Devanti it must masquerade another brand just like other house brands do Kogan Bauhn JVC etc that are China made

[fzabkar]

http://markingcodes.com/search/c/01%3D

The resolution of your PCB photos is too low to be useful.

I would disconnect the PSU from its loads and ground the PS_ON pin.

[phred01]

Tried to be frugal with pix sizes    Here are some new pixs BTW PS_ON are actually two independent pins from my measurements The smd pix is not that professional because of  lighting but it does show up  the marking

[fzabkar]

The link to the PSU PCB now points to the IC.

The IC is probably a RT7294AGJ6F -- 2.5A, 18V, 500kHz ACOT Synchronous Step-Down Converter.

https://www.rxelectronics.nz/datasheet/44/RT7294AGJ6F.pdf

The usual way to test the PSU PCB is to power it on using the PS_ON input. You need to see where this pin (pins?) goes.

[phred01]

located two more SMPS but cannot find data sheet fo Mstar chip MSH6103A

[fzabkar]

The pinout for the MSH6103A is in these service manuals:

https://181.119.56.37/Base%20de%20Conocimiento/PHILCO/TV/LED/SMART%20HD/91PLD32HS9B/Manual%20de%20tecnico%2091PLD32HS9B.pdf (page 46)

https://adjuntos.yoreparo.com/default/0006/97/d8022241fed88ec035aed66e43ac4752e25a33c6.pdf (page 24)

https://www.520101.com/files/newfile/20230605/e3048160759b21ee96460c13b3c12dc8.jpg (application circuit)

[fzabkar]

When you edited your pix, you messed up the link to Devanti PS.jpg. The thumbnail shows the board, but the link serves up an IC.

[phred01]

here is hires orignal pix

[phred01]

amazing msh cct that provides 0.95v supply to the cpu Still wonder STV-668-UHD-55BK is sold else where in the world and is there a service manual

[fzabkar]

Based on the numbers on the PCB, I'd say your TV was based on an MStar MSD6886 SoC. FWIW, a Google search turns up numerous references to HiSense TVs that use this SoC.

Look at the PCB at this site:

https://konmeiusa.com/products/msd6886

https://konmeiusa.com/cdn/shop/products/image61_900x900.png?v=1582069416

The part numbers are similar, as is the heatsink.

https://konmeiusa.com/pages/about-us

"Konmei – Konka Authorized Agent for OEM/ODM/Private Label Business"

To me, it looks like you have an OEM Konka TV.

[phred01]

All so call brands are actually of Chinese origin What the Chinese will do is put your brand on their generic TV.......called badge engineering Tracked down similar TV on Flea Bay......KOGAN KALED55NU8020SZA  Also suspect Eko TV sold by Big W as there are 2 models that might be similar. Purchased from Flea Bay KOGAN KALED55NU8020SZA main board + PS, These two boards are identical but may be different variant of the same item So instead the Devanti logo it will be Kogan. As far ps board the version number is also different and hope this production line variant. Will keep posted on progress

[phred01]

Update Finally power connector came from AliExpress Made up breakout connector board so the board can be fired up from a conventional PS. Power up the sucker noticed the red led flashed then the dual LED stayed Black. The Audio PCM output light when on. Checked the outputs of three down converters The RT7294A was working fine the voltage out was 5V Similarly The other down converters HSH6103A & RT6206BH both out puts were 1V. Obviously the CPU was not running. Powered up the 240v the original Power Board no 12v output. Wonder what killed the main board? Got from Fleabay The Kogan main board was put on my test bench ...powered up the main board Was greeted with a red standby light and turned it on with the power on button The red Led turned off In a short time the green on LED lit up followed by the PCM audio firing up. It appears the Divanti main board is cactus. Next step will install the Kogan Mainboard & power unit

[phred01]

Been doing more scouting on fleabay suspect JVC 55" model has the same main board

[phred01]

Great news the sucker is working again! KOGAN KALED55NU8020SZA main board did the trick O I have a Devanti coming up as a Kogan signon screen All else the same works well with the Devanti remote The two models are identical Kogan & Devanti engaged in Badge Engineering
learnt a lot about diagnoses
1 See if light in main board glows red and turns green if turned on via remote If it flicker red quickly and does not go green then board is cactus
2 Screen black if the above is OK LED back light has blown LEDs