I am fixing failure TV(no power on) . Failure occured after about 400 days from purchasing TV. I checked main board and found that output wave form of MP2238 is abnormal. MP2238 : 12V input, 1V output for SOC. Output wave form is not normal just after power on, so SOC does not start and boot process does not run. I touched ceramic capacitor by solder iron for 1 - 2 seconds , waveform became normal and SOC started boot process and TV normaly power on. But by icing capacitor , failure returned. input capacitor , output capacitor , VCC capacitor, whichever. And after cutting pattern of board ( MP2238 output to SOC) failure disappeared. I replaced MP2238 , ceramic capacitor , inductor , phenomena did not improve. At initial current of 1V line was 0.7A. Abnormal oscilation happens? or SOC became bad? or other parts became bad? Could you kindly advice for fixing or how to confirme failre cause?
Hello,
Thank you for reaching out on the MPS Forum.
Sorry to hear your having issues with the MP2238. The waveform you provided indicates to me there may be some instability in some enabling signals. Without a schematic, it is difficult to pinpoint if there is a fault with the external components or the converter itself.
Can you please probe EN (pin 1) and SW (pin 2,8)? Which ceramic capacitor did you touch with the soldering iron? Can you provide a photo?
If removing the output from the SOC resulted in normal behavior by the MP2238 and replacing the power circuitry, I can suspect there may be an issue with the SOC.
Thank you very much for your kind support. Here are waveform and photo and circuit. I am also suspecting SOC. This phenomena is before SOC application starts. So firmware in eMMC is not matter. I would like to replace SOC by new one but it is easy to fail. BGA replace is difficult… And by heating capacitor , SOC runs normaly.PCB issue? Anyway I really appreciate your support.
Hi @fixer.TV1 ,
Thanks for sharing SCH and the waveforms. From what it looks like there is an issue with the output sense resistors. There is some thermal derating that can occur during prolonged use. Since the feedback voltage is dropping resulting in no output I would recommend replacing the feedback resistors, as they could have been degraded and thus affect the control scheme for this part. For a 1V output. you can try to use the following config.
I would also suggest looking for any shorts or open connections to the SOC pins. The output voltage looks as if it is trying to recover from a protection.