XPost: sci.electronics.design   
   From: cd999666@notformail.com   
      
   Gentlemen,   
      
   Last week I got an old (1968) pulse generator out of mothballs and managed   
   to get it fully functional again. However, before replacing the case, I   
   (true to form) dropped it on the bench and something on the PCB must have   
   shorted out against the metal tools it fell on, because it no longer works   
   properly.   
   I've found an issue with the principal oscillator. It's generating   
   distorted sine waves. It's a wien bridge type using BJTs as the gain   
   element and fine tungsten filaments as thermistors, so should produce near   
   perfect sine waves before they're chopped and shaped by subsequent   
   circuitry, but since the fall, it's not.   
      
   Here's the oscillator output:   
   https://disk.yandex.com/i/eKAe95xMsiIvNA   
      
   I found some weird periodic spikes on the power supply rails in the   
   oscillator stage. They are actually present on the rail, not just picked   
   up by the ground lead of the scope out of the ether, as I used a short   
   ground clip in this instance. I'm not sure if these could cause the   
   distortion or not.   
   https://disk.yandex.com/i/eKAe95xMsiIvNA   
      
   I'm out of ideas. What could cause such distortion if the PS rail isn't   
   responsible?   
      
   Your pal,   
      
   CD.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)