Has anyone got, or know where I can purchase, a schematic diagram, for this TV, Power Supply Board, CVB42001. This board is commonly used in LED TVs. I'm chasing a problem in the output voltage, that feeds the LEDs Strips. Tks.
this TV, Power Supply Board, CVB42001. This board is commonly used in LED T Vs. I'm chasing a problem in the output voltage, that feeds the LEDs Strips .
around 32-35 (don't remember specifically) but leds don't light up. I chec ked all leds one by one - seems all right.
Without knowing the correct voltage drop across each LED (they vary quite a bit), you don't know what the correct voltage for the string is, and even if the service manual was available (it's most likely not), they wouldn't t ell you that anyway.I've seen strings that run as low as 25 volts and some that are over 200V.
Did you check the bklt_on and the PWM commands from the main? If these are missing or wrong, your LEDs won't light.
If it is related to the power supply, often the problem isn't the LED drive part of the smps but the PFC circuit back at the main. If this voltage st ays at bridge voltage, the higher load secondaries usually won't run.
OK. I see what you mean. But I have problem understand how does PFC or any other logic board would be able to control LED. The only connection power board has with main board via these 6 pin connection. The only interesting bits here are ON/OFF and ADJ. Not sure if any of these would control output of the LEDs power output on other side of the power board:
John-Del, I've looked a bit more. I found labels on back side. One of the inputs from FRC Board is "ON_BACK", and there is also "P_ON" both are zero V when turned off, and when I press power the both get up to 3.2V "EN" and "ADJ" that goes to power supply board are at GND level at all times. The backlight voltage shows 25.8 when turned off, and 32.3 when turned on. I don't have a oscilloscope to see what kinda of shape this signal is. I still don't understand how does power supply "decides" when to change backlight voltage if "EN" and "ADJ" don't seems to be changing at all ... or maybe I measuring wrong.
On Saturday, February 27, 2016 at 12:59:31 AM UTC-5, Aleksandr Motsjonov wr ote:
inputs from FRC Board is "ON_BACK", and there is also "P_ON" both are zero V when turned off, and when I press power the both get up to 3.2V
. I don't have a oscilloscope to see what kinda of shape this signal is.
acklight voltage if "EN" and "ADJ" don't seems to be changing at all ... or maybe I measuring wrong.
First you need to determine if you have a floating ground on the LED strips . You can do a resistance check from the ground plane of the power supply or metal frame of TV to either side of the LED connector. If one side read s zero ohms, use the frame or ground screw for your LED voltage. If not, l ocate a large electrolytic near the LED output section. This will have a v oltage rating of 100 to 450 volts and the neg side of the cap will make a g ood ground. There are several ways the LED voltage is varied on these. So metimes they actually vary the DC output, other times they use a mosfet on the low side of the LED strips and modulate the gate to provide the proper voltage drop across the string. Your reading is odd. It clearly is changin g voltage but there doesn't seem to be enough difference between off and on to go from LED cutoff to full bright, but I could be wrong on this.
To answer your other questions takes some more guessing (again, no SM). In standby, the SMPS will put out either 3.3 or 5v typically for the main. Th e P_ON command from the main turns on the other outputs of the SMPS, such a s 9, 12, 24 as required for the rest of the circuitry. In some TVs, this a lso turns on the PFC circuit (if equipped). When the PFC turns on, you'll see a big bump of voltage on this cap. Other boards will use a command fro m the inverter drive IC to turn on the PFC (rare). Still others use the su ccessful power up of one of the other secondary supplies to turn on the PFC .
Not all configurations use the adj and enable lines, particularly the real cheap TVS. Is your "EN" line also the "ON_BACK" line? You can try floating the adj line to see if the backlight voltage increases.
Most times if a TV's status LED reports a start when the button is pushed a nd successfully turns on the power supply, the main is OK (but not always : (. I've seen some Vizios that will turn on everything but the backlight bec ause the PWM (brightness) is missing.
The secret to all of this is datasheets. If you can find the datasheets fo r the LED drive IC (and PFC if it's equipped with one) you can go a long wa y with the proper pin outs, typical voltages, sample circuits, and descript ions of signals the ICs use.
On Sunday, February 21, 2016 at 4:32:57 PM UTC-5, Aleksandr Motsjonov wrote :
y other logic board would be able to control LED.
se would control output of the LEDs power output on other side of the power board:
I see an 8 pin connector on the close up that has two commands. If that is the only connector then the LED section is turned on with the rest of the power supply. The adjust will adjust the brightness of it. Because the ma in and smps/inv seem to be made by two different companies, they label them differently but I believe the enable and on/off turn on both the power sup ply and LED drive. If both of those go high, odds are very high that you h ave a problem either in the smps or an open LED.