From: not@telling.you.invalid   
      
   Hello, this was going to go to sci.electronics.repair but it   
   seems that Aioe users are blocked from there, so I'm posting   
   it here instead.   
      
   I recently bought a broken "cocktail" style arcade game   
   machine made in 1980. Initial repairs were easy. I got the   
   machine to start by playing with the connections to the CPU   
   and logic boards and fixed the lack of green on the monitor's   
   display by soldering the green lead of the RGB signal back   
   onto the monitor board.   
      
   The problem I'm left with is that after about three minutes   
   (less if it has been recently used), the picture on the   
   monitor is reduced to some coloured vertical lines and a   
   whining noise is emitted. Before this, the display bends   
   inwards at the bottom (and a bit at the top) of the screen. My   
   assumption has been that this is a sync issue so the first   
   course of action was to look at the sync signal that goes from   
   the CPU board to the monitor with my Oscilloscope. I did this   
   expecting to see a slowly worsening waveform, but instead I   
   saw what seemed to my eye a quite nice saw tooth.   
      
   However what did catch the attention of my untrained eye was   
   that this waveform varied by less than a volt between 4 and   
   5V, except for a momentary drop to 0V at the end of the wave.   
   Period of the waveform was 90uS.   
      
   I only have theoretical knowledge of monitor sync signals, so   
   I didn't know what to expect, but it seems to me that this is   
   an oddly small voltage change for such a signal. I tried to   
   find something on the web that would tell me if this is the   
   case, but failed. Hence I ask here.   
      
   Thank you for reading.   
      
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