|
I finally have a coherent picture on this set.
I've been beating my brains out the last couple days on a Horizontal frequency problem, I couldn't get less than three side by side images no matter how I adjusted it.
I checked and rechecked my work, rechecked resistors, rechecked the power supply wiring, still nothing.
I finally decided the problem must be in the Phase inverter section, a quick check of the voltages on the 12AU7 found 60 volts on pin one where there was supposed to be 27.
I checked the resistors around the tube, all OK.
I finally decided to switch the Phase inverter 12AU7 with one in the i.f. section and that's when I found the problem.
Someone had put a 12AX7 in place of the 12AU7, they look similar but are not the same at all and it wouldn't allow the Horiz Oscillator to run at the right frequency, on top of that when I switched the tubes around it caused a short in the 6CB6 i.f. tube that smoked the resistor.
The 12AX7 had the markings rubbed off and I took it on faith that it was the correct tube, if I had put it in the i.f. strip first I would have been chasing a different problem.
I found a 12AU7 and another 6CB6 and bingo, I was able to bring the picture into sync!
I love those Aha! moments when you finally solve a problem that's been driving you nuts.
The horiz is still a little drifty, possibly some resistors changing as they get hot or maybe the Micas going bad, but at least there's one less problem to solve.
|