From: petrus.bitbyter@hotmail.com   
      
   "Computer Nerd Kev"  schreef in bericht   
   news:XnsA160D3628E09BCSKJHNMW985780A@94.75.214.90...   
   > 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.   
   >   
   > --   
   > __          __   
   > #_ < |\| |< _#   
      
   Apparently something wrong in your horizontal drive signal. Most likely the   
   line output transformer, maybe the horizontal coils but there are still some   
   other possibilities. Be aware that the coils are current driven.   
      
   petrus bitbyter   
      
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