[R-390] OT: Update on Blaupunkt

[Les Locklear]

I've seen several bad dogbones in 51J series receivers. YMMV

Les Locklear
Gulfport, Ms.
DX'ing Since '57








  ----- Original Message ----- 
  From: Barry 
  To: r-390 at mailman.qth.net 
  Sent: Tuesday, January 25, 2011 8:25 AM
  Subject: [R-390] OT: Update on Blaupunkt


  Since I posted some of the problems I've been having with the IF transformer in the Blaupunkt Verona I've been working on and since we've been discussing capacitor replacement, I thought I'd post an update.

  You might recall that I was having a problem getting the secondary of the 1st IF transformer to resonate.  Pulling the transformer and checking it out-of-circuit showed the transformer was good so I reinstalled it and kept looking.  I found that, when switch to AM, the screen voltage of the IF amplifier would go low (approximately 1/2 of what it should be) and then found that the control grid was also going slightly positive (which would cause the screen voltage to drop).

  Not finding any other source of a positive voltage influence on the control grid, the only thing left was a 4700pF dogbone ceramic(?) capacitor tied from the screen to the "low" side of the IF secondary.  I lifted one end of that capacitor and put a temporary 4700pF disc ceramic in its place.  Voltages are now restored to what they should be and the secondary resonates quite nicely and the culprit turned out to be a dogbone capacitor.

  The dogbone ceramic would have been my last suspect.  It's still hard for me to believe it could have been that leaky.  The paper capacitors would have been the ones I would have shotgunned and left the dogbone alone.  All that work and the radio would still not have worked properly.

  Draw your own conclusions I suppose...

  Barry - N4BUQ

  ______________________________________________________________
  R-390 mailing list
  Home: http://mailman.qth.net/mailman/listinfo/r-390
  Help: http://mailman.qth.net/mmfaq.htm
  Post: mailto:R-390 at mailman.qth.net

  This list hosted by: http://www.qsl.net
  Please help support this email list: http://www.qsl.net/donate.html