0
\$\begingroup\$

I have a Hisense TV HLE4815RT (mainboard: RSAG7.820.5649), that suddenly stopped tuning cable signal, it just says "No signal". I tried different cables, removing some splitter, reprogramming the channels and still doesn't get a signal on any channel. A different TV works on the same cables. A few times, ramdomly, when turning it on it picks up the signal for 1 second with normal quality, and then loses it.

All the other functions work fine, hdmi and usb port (have a chromecast connected), all the smart functions and everything else works normally. That's why I suspect it may be an issue on the tuner. I do not have any experience repairing TVs, I just like electronics and do some arduino stuff as a hobby.

I opened the TV to check for any obvious issue like a burnt component but couldn't find anything. I measured the voltages on the tuner pins:

And see that where it says 3v3 it's actually receiving 3.69v. In the datasheet for the voltage regulator 1117A (N19 in the pic) that seems to power the tuner, it says Max Vout is 3.366v. In google, I found that the tuner (CDT-9051324-10) uses the chip NXP 18273, whose datasheet shows a Max Vin of 3.6v.

The Vref measured between the GND/ADJ and Vout pins of the 1117 regulator have 1.35v (in the datasheet it says it should be 1.25v). The two resistors R398 and R399 have the correct value according to page 14 of these diagrams (110 and 180 ohms).

Is the 3.69v coming from the regulator between the acceptable range or could it be malfunctioning and causing the tuner to not work?

\$\endgroup\$

1 Answer 1

0
\$\begingroup\$

The Vref should be 1.25V between 3.69-2.29=1.4V

In order to lower Vout to 3.3 you must add resistance between those two pins to lower Vout.

IDK the R values used, start with 220 to 470 Ohms to get a 3.3V output .

Vref is either 1.4 or 1.35 shown due to incorrect R values.. It is between ADJ and should be Vout-Vadj = 1.25V. The R =Values they used may have tried to get 3.6Vmax but due to tolerances (10%?) failed to achieve that.

enter image description here

Link not avail, but site is shown.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.