Ok. Let’s try this again…RCA 9TC240 Alignment

[Chris K]

Originally Posted by bandersen

What volts/div are you using on the y-axis? Could be you are viewing a very low level signal and there is a lot of noise.

Not in front of it right now but I believe you are right as I needed to up the Y-axis signal quite a bit to get a trace with enough amplitude so I could see a discernible shape. I'm attempting to do the first audio adjustment requiring the sweeper and marker for the 9TC240 and get the discriminator waveform correct.

[bandersen]

Did you try increasing the output level of the sweep gen?

[Chris K]

Yes I did...no discernable improvement.

[Chris K]

Input of a 21.25mc 0.1V (and up) RF signal swept symmetrically 1mc into the grid (Pin 1) of the 2nd sound IF and the scope Y input from the junction of C183 and R215. Generator sweep output to the horizontal scope input. Regardless of the fuzzy signal, I was not able to get the Fig. 15 symmetrical positive/negative trace with adjustment of T-113.

[bandersen]

Changing the output level of the sweep gen has no effect on the height of the waveform on the scope? It should have a drastic effect.

Then either the sweep gen isn't working or you have something hooked up wrong.

Does the scope display change if you vary the center frequency? Can you see the markers?

[Chris K]

Sorry Bob...I just zoomed in on the picture on my phone. That is at the highest output on the sweep gen. Anything lower and it begins to flatline quickly (if I'm remembering that correctly). I don't think I tried to vary the center frequency when it was hooked up to the TV

[Chris K]

Markers are very visible

[bandersen]

What cable are you using to inject? Is it the original for the sweep gen? You may need to terminate with 50 or 75 ohm resistor. Without proper termination the generator can't accurately track the output level.

Also, what are you using for the Y input on the scope? A X10 scope probe? Demodulator probe?

[Penthode]

The noise could be due to the wideband scope. Does the scope have a lower bandwidth setting to limit below 10MHz? Try clipping a 1nF capacitor across the probe feeding the scope.

[Chris K]

Originally Posted by bandersen

What cable are you using to inject? Is it the original for the sweep gen? You may need to terminate with 50 or 75 ohm resistor. Without proper termination the generator can't accurately track the output level.

Also, what are you using for the Y input on the scope? A X10 scope probe? Demodulator probe?

The sweep gen did not come with any cables. Just using a BNC cable hookup to the RF and injected into the IF circuit with signal and a ground alligator clips.

1X setting on scope probe out.

I have RF inject and demod out cables from the EICO that were aftermarket builds by an eBayer who builds probes for all kinds of vintage equipment and his stuff is highly rated as I bought probes for my Heathkit VTVM from him. The issue is the probes do not terminate in male BNC hookups. They are the old style with a central solder spot in the center of a phenolic with a screw in ground. I would need to cut them up and modify them to use them. Not opposed to that since the Eico didn't work well.

[bandersen]

Maybe, but he shouldn't need to have RF out at 100% to see something should he?

[Chris K]

Originally Posted by Penthode

The noise could be due to the wideband scope. Does the scope have a lower bandwidth setting to limit below 10MHz? Try clipping a 1nF capacitor across the probe feeding the scope.

I don't think so but what do I know about scopes? You're saying put a 102 cap on the scope out signal?

[bandersen]

No, he's saying 102 cap from the scope input to ground. You should really have the end of your RF out terminated. Without it, the RF output level meter is meaningless.

Do not use a demod probe. Use a 10X scope probe. You will rarely if ever use a scope probe in anything but X10 mode. It loads down circuits in X1 mode.

[Chris K]

Originally Posted by bandersen

Maybe, but he shouldn't need to have RF out at 100% to see something should he?

RF out is at 1 volt. The manual says 0.1V. At 0.1 I get a trace about 2 1/2 grid squares vertical on the scope

[Chris K]

Originally Posted by bandersen

No, he's saying 102 cap from the scope input to ground. Oh use x10 scope probe. You don't need a demod probe

I'll try it