Two VERY general questions!

Discussion in 'General Electronics Chat' started by Nicholas, Nov 27, 2007.

  1. Nicholas

    Thread Starter AAC Fanatic!

    Mar 24, 2005
    121
    1
    Hey all!

    I have a monitor board that isn't working, so I have two questions I would
    like to ask you!

    The first is about a resistor on the board. It's color coding says it should
    be 1Mohm, but it reads as 247ohm every time! What could be wrong here?

    The other is a picture of the solder side of the board, at what seem to be
    one of the HV legs. What is going on here, what is that splotch?:

    [​IMG]

    Thanks,

    Nicholas
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    You may need to desolder one leg of the resistor and lift it to get a good measurement. There could be anything in parallel with it, which would give an incorrect reading in circuit.

    That blotch could be bad, but there is not quite enough resolution to make it out. What is connected to the other side of the hole?
     
  3. Nicholas

    Thread Starter AAC Fanatic!

    Mar 24, 2005
    121
    1
    Hey! Thanks!

    I'll try to remove it then.

    The high voltage thingy that powers the CRT is connected to the other side of the
    hole. Do you think I should re-solder it? And what IS that brown stuff anyway?

    Thanks,

    Nicholas
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Not enough detail visible to say. The size of the copper trace might suggest it's circuit ground, but that's a guess. The split peg visible could be a locating pin. The brown stuff around the hole might be the PCB substrate, some kind of phenolic.

    A high voltage thingy is more properly called a flyback transformer, by the way. Problems with them are usually more expensive to fix than getting a new monitor.
     
  5. mrmeval

    Distinguished Member

    Jun 30, 2006
    833
    2
    It looks like a ground pin. Power off the unit, unplug it. Soak a qtip in alcohol and see if the brown gunk will remove. If it does it's flux. It's probably a wire that was hand soldered from the CRT board to the main board.
     
  6. Nicholas

    Thread Starter AAC Fanatic!

    Mar 24, 2005
    121
    1
    Thanks!

    Is flux from a solder joint conductive??

    Nicholas
     
  7. Management

    Active Member

    Sep 18, 2007
    306
    0
    I don't think so. I thought it was only for causing a better flow of the solder when melted.

    EDIT: Looked this up. I guess it depends on the sensitivity of your circuit. Best to clean it off a little after soldering.

     
  8. JoeJester

    AAC Fanatic!

    Apr 26, 2005
    3,373
    1,157
    The brown stuff looks like flux to me. I certainly would remove that solder, make sure it's supposed to be connected to that pcb run, and renew the connection. It does look like the tab of a flyback transformer.
     
Loading...