How to troubleshoot IF strip

[old_tv_nut]

Originally Posted by miniman82

Thanks to CTC17, I have some direction now.


Here's what I did tonight:

First trace is the output from the 415 right into the scope, with markers shown by the text. I don't know why it shows up reverse of what the Sams sheets show, but it is what it is.




Next in order to check overall alignment, Sams has you inject at the mixer crystal through an 'input head' which consists of a 68-ohm resistor to ground followed by a series 1500pf cap into the crystal. I don't have that, so I made the connection directly with the 75-ohm leads and the 415 function switch on IF. Doesn't look like it's supposed to: the double humped part isn't flat topped at all, and the markers on the right hand side are not where they are supposed to be at all.



Next I set the 415 function switch to channel 4, and attached to the antenna terminals. It seems like something in the areas of 41~42Mhz isn't peaking at all, or some other strange shift in overall response has occurred. Opinions?

I found that curve with the mixer injection is extremely sensitive to loading on the CTC-5 - need to have very short leads and the correct value of coupling capacitor, even then, without a photograph of the factory recommended coupling network, your mileage may vary.

The channel 4 result looks good to me EXCEPT that the fine tuning is off. The 45.75 video carrier should be halfway down the slope on the left, and then the color frequencies will move up on the curve more on the right, and the 41.25 sound will be at the bottom of the right skirt.