VHF Tuner Alignment: where is the overall oscillator adjustment?

[LukeSimon]

Originally Posted by Yamamaya42

From what I have seen of the videos posted to u-tube about this, there is no such thing as a “perfect” IF or chroma bandpass alignment, just varying degrees of ALMOST there!

I struggled for a while because the TV was so badly out of alignment. There are so many adjustable slug coils and pots that need to be adjusted, I amost ran out of alignment tools. If one of the slugs is far from correct position, the gain is terrible and adjustment doesn’t seem to help. Every slug I turned would make the bode plot look worse. So I figured, I try large changes in slug positions and by trial and error “explore” for a combination of slug positions that simply gave better gain. Ignoring shape and focusing on gain at first allowed me to get to a slug combination where all slugs and pots started to behave like their description in Magnavox’s manual.

The markers 42.17mc and 45.75mc are supposed to be at 50% +/- 5% down the curve and they are currently at 49%. 42.75mc and 45mc are supposed to be 85% +/- 15% and they are currently at 78%. The 47.25mc trap is just slightly off from being perfect too.

I can only imagine what negative gain was doing to the chroma signal. It is impressive that the TV was able to draw a picture with how badly it was misaligned.

Alignment would absolutely be impossible to achieve without the proper tools, and even with the proper tools, it takes lots of trial and error.