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Nie, dziękuję Przekieruj mnie tamhow can i check internal voltages on a LED40TD SABA TV?
Yes—you can check the internal voltages with a digital multimeter, but do it on the secondary/cold side of the board, not in the mains section. If your SABA LED40TD uses the TP.SIS231.PT85/PT851 family combo board, the most useful checkpoints are:
Also, do not assume the backlight rail is a simple fixed 24V. In this chassis family, the LED driver outputs are panel-dependent constant-current outputs, and the specification shows nominal LED string voltages ranging roughly from the low-30V range up to about 57V, depending on which LED connector version the board uses. (electronica-pt.com)
Your TV likely uses a combo board architecture, where the AC input, power conversion, LED driver, and main logic regulators are on the same PCB. The chassis document shows:
That matters because the correct troubleshooting sequence is:
Use your meter’s black probe on secondary ground:
With the TV plugged in but still in standby:
The schematic shows UL1 = LC1117CLTR33, converting 5V_STB to 3V3_STB. If these are missing, the TV will usually appear completely dead or will not respond correctly to power-on. (electronica-pt.com)
When you turn the TV on:
These are not guesses—the chassis troubleshooting flow explicitly tells the technician to check:
If the logic rails are correct but there is no picture, check VCC_Panel at CN12 pins 1 and 3. The troubleshooting flow for this chassis specifically points you there. It also indicates the switched panel rail can be 5V or 12V, depending on panel configuration and the panel power switch path around QM1/QM2. (electronica-pt.com)
Only check the LED outputs if you are comfortable working around boosted DC rails. The chassis specification lists several possible LED connector arrangements and nominal per-string voltages, including approximately:
So if you expected a simple 24V backlight supply, that expectation is probably wrong for this board family. The LED driver here behaves more like a constant-current boost driver than a simple low-voltage rail. (electronica-pt.com)
Use this interpretation:
No 5V_STB / no 3V3_STB
Suspect the standby section first. (electronica-pt.com)
Standby present, but no 12V at CNB3
Suspect the power section / 12V distribution path. The service flow starts with CNB3 for exactly this reason. (electronica-pt.com)
12V present, but no 5V at LD1/CD29
Suspect the local 5V buck stage around UD1 or its enable path. (electronica-pt.com)
5V present, but no 3.3V at UL11
Suspect UL11 or a short on the 3.3V rail. (electronica-pt.com)
3.3V present, but 1.0V or 1.5V missing
Suspect UD41, UL61, or a shorted CPU/DDR load. (electronica-pt.com)
Logic rails correct, but no image
Check VCC_Panel at CN12, LVDS cable seating, and then the panel/T-Con path. The display troubleshooting flow explicitly points to VCC_Panel and CN12. (electronica-pt.com)
A useful correction to many generic TV-repair guides is this: on these integrated TV chassis, the “backlight voltage” is often not a fixed 24V rail. The available chassis documentation for the TP.SIS231.PT85 family shows multiple LED output connector options with different nominal voltages and currents, which is typical of panel-dependent LED driver implementations used in low-cost LED TVs. (electronica-pt.com)
Another practical trend is that these boards integrate more functions onto one PCB, which means a fault in one section can pull down other rails and make diagnosis confusing unless you check the rails in dependency order: standby → 12V → 5V → 3.3V → 1.0V/1.5V → panel/backlight. (electronica-pt.com)
Think of the board as a power tree:
If one upstream rail is missing, the downstream rails will also be missing. For example:
This is why random probing is inefficient. Follow the dependency chain.
Best practice:
The exact connector population can vary. The chassis document itself notes that some connectors are optional, and it lists several LED output connector variants with different voltage/current values. So always trust the silk-screen printed on your actual board over a generic internet diagram. (electronica-pt.com)
If your board number is not TP.SIS231.PT85/PT851, then the rail names may still be similar, but the exact checkpoints can change.
If you want, send:
Then I can tell you much more precisely whether the fault is in:
To check internal voltages on your SABA LED40TD, use a multimeter referenced to cold ground and verify the rails in order:
The most important correction is that the LED backlight output on this chassis is not necessarily 24V; it can be significantly higher and depends on the panel/connector version. (electronica-pt.com)
If you send me a board photo, I can mark the exact points you should probe.
