Help reading schematic voltages input/output

Collapse
X
Collapse
+ More Options
Posts
 
  • Time
  • Show
Clear All
new posts
  • mon2
    Badcaps Legend
    • Dec 2019
    • 13902
    • Canada

    #21
    Second one seems like misbehaving right? Should I remove it for testing outside board?
    Yes. Good find.

    Comment

    • gjgib
      Senior Member
      • Nov 2022
      • 70
      • Venezuela

      #22
      PQ3502 out. Behaves like it's meant to. SD 0.5V / DS blocked. I didn't know it could behave shorted in diode mode just because of the low core rail impedance? Or it shouldn't show shorted behavior even like that?

      Measuring PQ3502 pads alone in resistance mode gives this: DRAIN- 58Ω SOURCE- 0Ω and GATE- 5.3MΩ​. Mosfet still off board.

      Comment

      • mcplslg123
        Badcaps Legend
        • Jun 2015
        • 7262
        • india

        #23
        Resistance to GND on any rail is a relative concept and not absolute concept. You cant put a fixed number as it varies from platform to platform. Resistance to GND on cpu core at 0.9ohms on vcore is fine for a 9th gen gaming board but may be considered short for a 6th gen cpu. Similarly GPu coil resistance to GND on a gaming laptop may be fine at even 0.1ohms but its definitely shorted for a normal notebook motherboard. Have seen 100 ohms resistance to gnd on ram coil as well as more then 500oms on the same rail in other board. So in a nutshell, there is no yardstick to conclude what can be considered shorted and it will vary from platform to platform. Only experience will help you in right conclusion.

        Comment

        • piernov
          Super Moderator
          • Jan 2016
          • 4435
          • France

          #24
          Low-side MOSFET is in parallel with CPU, so it measures the same as expected.
          OpenBoardView — https://github.com/OpenBoardView/OpenBoardView

          Comment

          • gjgib
            Senior Member
            • Nov 2022
            • 70
            • Venezuela

            #25
            mcplslg123 Oh my, I thought I could've made my journey easier but it seems like I have to fight every board to learn. Thanks for insight.

            piernov Thanks again. I think I'm running out of options. Getting closer to swapping the IC. Any suggestions to not burn such complex IC while hot air-soldering a replacement?

            Comment

            Related Topics

            Collapse

            • EasyGoing1
              Reading input and output of bridge rectifier on the same scope?
              by EasyGoing1
              I have a 40 volt AC transformer that I put a bridge rectifier on, and I wanted to see the input signal and the output signal on the same screen on my scope, so I set one channel up with the test lead on one side of the input and the ground lead on the other side of the input, then I used another channel on the scope and clipped the test lead on the positive side of the output then the ground on the negative side of the output.

              When I connected the transformer to power, the wire that was connected between the ground lead on the second channel and the negative side of the bridge rectifier...
              06-26-2022, 12:52 AM
            • tvguy12012012120
              Zombie Samsung UN55NU6900F dead / no standby voltage - randomly came to life after hours of troubleshooting then died
              by tvguy12012012120
              This is my first attempt at troubleshooting a board like this, I know I could just buy a new board but I'm curious to figure out how this works. I've been testing different components in the evenings this week and I think the problem is with the IC failing to start up for some reason. When the board is plugged in there is no standby voltage.

              Then today it randomly sprung to life like a zombie but shortly died thereafter. I have no idea why it would have done that and its the first time I've seen it running. I discharged capacitors on the board last night, then it was sitting today....
              02-07-2025, 05:13 PM
            • redbaron1007
              Yamaha HTR-3065 No power/No Standby
              by redbaron1007
              I got a Yamaha HTR-3065 on the bench currently that's got a no power/ no standby issue.When I plug it in it draws 0.01A from the wall, the relay for the ac transformer never clicks, there are no standby lights on the front, and pressing the power button does nothing. The fuse was not blown but upon measuring the voltages on the power low voltage power supply board (labeled operation 3 pg 89 in the schematic) they do not match what the schematic says they should be.
              S9 13.7V

              Pwr Ry 0V
              AC Det 9.1V
              Mgnd 0V GND

              The two pins on the transformer for the operation...
              09-12-2024, 03:04 PM
            • dennis_elx33
              3PHASE STEP-DOWN Transformer in Check
              by dennis_elx33
              Hello All,

              i would like to post an interesting topic regarding 3-phase stepdown transformer which we suspect to cause an overcurrent (138A) which resulted to power tripped off of the HV power supply (80KV output).


              Problem statement: Power tripped Off

              Initial Problem: Found 2 IGBT and 2 rectifier diodes shorted (burnt).

              Action Done:
              1) Replaced the faulty parts with good spare.
              2) Measured impedance of the 3phase input lines and found that L2 to L3 has 23.3ohm while other pairs are 51Kohm. This pins will...
              12-02-2024, 06:52 AM
            • eigma
              Samsung UN40H5003 boot loop every ~8 seconds
              by eigma
              Hi, I rescued a Samsung UN40H5003AF (H = 2014 FHD) from the curb. Symptoms are: standby (red) light comes on, stays on for 8 seconds, flickers off, then comes back on, and the cycle continues.

              Service manual: https://www.electronica-pt.com/esque...is-u8la-71272/

              SMPS board: checked voltages, all seem normal (A13V = 12.8V, UD = 3.3V, PWM_BLU = 0.77V, PS_OnOff = 5.5V). Remove 10p cable to main board -> backlight comes on. I think this means SMPS board and backlight are good.

              Main board: BN94-07592P / BN97-08922R...
              11-20-2024, 10:31 PM
            • Loading...
            • No more items.
            Working...