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LG 42PA4500 - YSUS does not start - the repair kit has been replaced

Ibuprom 8706 7
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Treść została przetłumaczona polish » english Zobacz oryginalną wersję tematu
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  • #1 16659052
    Ibuprom
    Level 26  
    Ysus ebr73575201. Standard fault - 5 transistors shorted. 2x G7S313U, 2x RJP63K2 and KF7N60. The VS short circuit subsided. The power supply starts by giving 204V on the VS line. There is also 5V from the power supply. Unfortunately, YSUS does not start. Samples but doesn't start. SUS_DN flashes between -80 and -60V. I checked the most important elements - I didn't find another short circuit. Higher power resistors also ok. On the side driver connectors I also did not find any short circuit.
    18V from converter to YSUS is missing - i.e. on the secondary side before the 18V stabilizer, it flashes between 2-4V.

    Any hint what to check?
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  • #2 16659195
    mirex
    Level 43  
    Disconnect buffers (scans, drivers). When you get 18V you already know.
    If not, then take a closer look at the 18V diode itself.
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  • #3 16659381
    Ibuprom
    Level 26  
    Disconnected - 18V appeared. The costs will come out big, but does this TV have a chance yet to come? How does this result from your experience? I would not like to make significant costs and have another fault related to the panel or drivers in 2 months.
  • #4 16659435
    mirex
    Level 43  
    Ibuprom wrote:
    The costs will be high
    Maybe it is enough to replace one integrated circuit? ;) One would have to fly an ohmmeter.
    And ... because I don't remember how it is ... maybe 18V on Y goes through the drivers?
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  • #5 16659461
    Ibuprom
    Level 26  
    I'll look tomorrow yet. Meanwhile, thank you for your help. I didn't think about disconnecting YSUS before.
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  • #6 16667832
    Ibuprom
    Level 26  
    I replaced the whole YDRV disc today because I didn't find any departure from any of the drivers. Unfortunately - the situation is unchanged. I have not found the schematic either, but it seems that 18V does not have a separate converter but is controlled from the converter generating SUS_DN. I also didn't find the 18V transition to the YDRV board. Nevertheless, it appears after unplugging YSUS from YDRV.
  • #7 16669696
    Ibuprom
    Level 26  
    I have measured it today. The 18V converter has separate control from NCP1200. 18V appears without YDRV connected. With YDRV pulsing. I did not detect a short circuit or change in resistance at the inverter outputs after connecting YDRV. The NCP itself uses only the optocoupler as the feedback signal, which seems to be working. On n. 6 VCC a filter capacitor is connected which is charged from the 8 HV leg. And on this capacitor, the voltage pulsates to the "ticking" of the inverter. Changing the resistor to VCC will not change this. I will try to substitute NCP, although it seems to me unlikely since voltages appear without YDRV.
  • #8 16673719
    Ibuprom
    Level 26  
    And I finished the repair with a fiasco. As it turned out - the YDRV bought had a short circuit on one of the drivers in the + VPP branch. The meter did not look like a short circuit but the current test indicated which one. Another driver was damaged in my YDRV. I desoldered the driver in my board. A second after turning on the power supply one of the IRG7S313U transistors was damaged (by the way I got 2 different samples loose, looking like a slightly corroded tin coating, which aroused my suspicion - purchase from tomelektron). After desoldering one, the other seems to work. Turn it on again - ZSUS transistors got shorted. At YSUS they still look functional. At the moment I finish the repair because of the costs.
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Topic summary

The discussion revolves around troubleshooting the YSUS board (model EBR73575201) of an LG 42PA4500 television, which fails to start despite replacing a repair kit. The user initially identified shorted transistors (2x G7S313U, 2x RJP63K2, and KF7N60) and confirmed that the VS line provides 204V and 5V from the power supply. However, the YSUS board does not start, with SUS_DN voltage fluctuating between -80V and -60V. Suggestions include disconnecting buffers to check for 18V output, which appeared after disconnection. Further investigation revealed that the 18V converter is controlled by an NCP1200, and issues persisted even after replacing the YDRV board. Ultimately, the user faced additional complications with damaged drivers and transistors, leading to a decision to halt repairs due to escalating costs.
Summary generated by the language model.
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