I'm looking for the user manual for Sinotec 40inch STL-40E3000 led tv, and also where can I find the manual control buttons on the TV itself

Question edited for clarity.

There is a rather 'round about' way of doing it and it starts with your computer!

Installing Apps using APK Installer on my Sinotec TV Home screen

• Open your browser on your computer, find the APK file you want to download, and select it.
• Once the App is downloaded, open Downloads, right-click on the APK file, then save to USB or external storage device.
• To install this APK from your storage device to the TV, plug the USB into the TV.
• On your HOME screen, go to APK installer, and select the APP you would like to install
• The app will begin installing on your device.
• After the application has successfully been installed the user can run the app with no issues.
• Please Note: Only selected smart models have the "Install APK" function.

https://www.sinotec.co.za/support/faqs/

Specs for your television says it comes with

• Netflix
• YouTube
• Twitter
• Facebook
• Mirashare
• Digital Dvb-T2
• Child Lock

Sinotec 58" UHD Android TV

Sinotec https://www.sinotec.co.za > product > sinotec-58-uhd-...
Open Browser: Yes; Prime Video: Yes; Netflix: Yes; DSTV Now: Yes; Showmax: Yes ... STL-58G50UM. Sinotec 58? UHD NETFLIX LED TV. Resolution: 3840 x 2160. View ...

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If the standby button on your Sinotec STL-32VN23 TV isn't functioning, and the red light remains on without changing to blue, it could indicate a power-related issue or a problem with the standby button itself. Here's how to troubleshoot:Confirm the TV is receiving power from a working power source.If available, try using the TV's remote control to turn it on.If the issue persists, unplug the TV from the power source for a few minutes, then plug it back in and attempt to use the standby button again.If the problem still exists, it may be due to a technical fault in the TV's power circuit or with the standby button. In this case, it's advisable to contact a professional technician or the manufacturer's customer support for further diagnostics and potential repairs.

Software is done via Wifi using the smart hub button. Firmware is done via USB. I don't like the third party sites in this link, get it from Sinotec's website

https://www.google.com/search?q=update+software+on+my+sinotec+smart+tv

how to upgrade software on Sinotec Smart TV model STL ...

https://satechhelp.co.za > how-to-upgrade-software-on-s...
Dec 5, 2019 - 1 Answer · Make sure the TV is connected to a Wi-Fi network. · Press the Home/Smart Home button on your remote to bring up your launcher bar.
1 answer · Top answer: Hello • Make sure the TV is connected to a Wi-Fi network. • Press the Home/Smart Home button on your remote to bring up your launcher bar. • Click ...

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  Software update for sinotec UHD TV STL-55E5600M

  https://satechhelp.co.za > software-update-for-sinotec-u...
  Turn on your Sinotec smart TV. · Make sure the TV is connected to internet. · Using your remote control => Go to the TV's options menu by pressing the "MENU" ...

Some help here, but it appears to be a South African television, and we are in North America. The search results may be better for you.

https://www.google.com/search?q=sinotec+STL+-43E3000G+remove+system+lock+password

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with no buttons on the TV actual, impossibe
can you drive a car lacking a steering wheel?
buy universal remote and program it
or buy the correct one off say flabay
off topic here , computers.

bad caps on power board
either repair caps.or replace the board


cheers

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Refer the TVs' user manual for details. Electro help