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

[Penthode]

Originally Posted by Chris K

Yes as you have said. Not gonna tell me which coil gets the shunt eh?? That’s ok…I’ll figure it out!

I told you! Even down to the connection letters written on the base of the transformers!

[Penthode]

Originally Posted by Penthode

The arrows pointing up mean the trap adjustment is on the top of the chassis. The arrows pointing down means the adjustment for the stagger tuned stage is made from under the chassis.
Each stagger tuned stage has a resonant coil which connects to T102 terminals A/B and T103 terminals A/D, T104 terminals A/B and T106 terminals D/C.

The resistors are placed across each stagger tuned coil.
There is really no primary and I don't know why you are hung up on that. There is the stagger tuned coil and the parallel tuned trap mutually coupled to it. It is clearly identified on the schematic.

Do you understand what you are doing by clipping in place the resistors? It is to eliminate the resonance of the stagger tuned coils so that the remainder of the video IF strip is just an untuned amplifier. This is so you can see independently the tuner over coupled transformer link frequency response when you sweep it. You must try and understand the process so so will be better able to identify and rectify any problems.

Here is is again

[Chris K]

Just making a joke…not a very good one I guess. Sorry if I offended you.

[Penthode]

I am never offended. That was my joke in return. I hope it did not offend you.

Are you all set? A good part of the process is identifying the pitfalls and knowing how to get out of them. I try to (and not always successfully) abide by the rule if something doesn't look right, stop and think about it before proceeding.

[Chris K]

So I went back to step 6 in the alignment procedure just to be certain the adjustments I made to the top and bottom cores with the different frequencies fed into the converter grid were accurate and that the VTVM was reading the minimizing/maximizing accurately i.e. checking my work that I had the trap coils tuned to the correct resonant frequencies and the IF stages tuned properly. A couple of days ago, I posted the issue with the VTVM going off scale was tied to the signal strength going into the converter and with careful adjustment of the signal output I was able to tune the traps and stages accurately without the VTVM requiring a voltage range setting higher than 5 volts DC. When rechecking tonight, I encountered the same issue. I could not get the VTVM to read in the 5V scale when measuring across the video amp load resistor.

I believe I've found what is doing this but how and what is happening I don't know. The brightness control seems to be a problem. It is intermittently grounding out and sending full voltage through the yellow wire to the CRT. A bright horizontal line appears on the screen. Touching the shaft will cause the VTVM to jump way out of range. I don't know if this is what is causing the issue with measuring the voltage changes that happen when I'm trying to tune traps and minimizing at the R119 load resistor but when it happens, the VTVM pegs and goes off scale.

I don't see how sending full voltage to the CRT cathode could be causing the issue. The only possible link I see may be the fact the yellow wire from the control to the CRT cathode runs directly under the load resistor I'm measuring to adjust the frequencies in the various stages. This has been an intermittent issue since I started doing this series of adjustments and I guess, when I worked on it a few days ago and reported no problems, it wasn't happening. So at this point, I don't know if I even have the trap coils adjusted correctly. I don't know enough about what that voltage spike in proximity to a test point in this effort could do. I guess I could move the wire and see if it helps.

[Penthode]

Just to confirm, with nothing connected to the VTVM and it set to 5 volts, it still goes off scale?

[Zenith26kc20]

The brightness control goes from 135 volts fed by a 12 K resistor going thru the control to ground. If it does pull a short to ground, the 12 K would overheat and possibly pull the 135 low. This 135 volt source feeds the I F screen grids also. If the control is grounding, check for tin whiskers on the control. Changing the 135 source in relationship to ground will, thru the screen voltages changing, affect the amplification factor of the I F and cause quite a change in the I F.
I would monitor the brightness control to ground as I rotate it for a drastic voltage change.

[Chris K]

Originally Posted by Penthode

Just to confirm, with nothing connected to the VTVM and it set to 5 volts, it still goes off scale?

Not sure I understand the question. Do u mean is there an issue with the meter? No there’s no issue. It works fine. I’ve tested ac dc and resistance with it and it’s dead on

[Chris K]

Originally Posted by Zenith26kc20

The brightness control goes from 135 volts fed by a 12 K resistor going thru the control to ground. If it does pull a short to ground, the 12 K would overheat and possibly pull the 135 low. This 135 volt source feeds the I F screen grids also. If the control is grounding, check for tin whiskers on the control. Changing the 135 source in relationship to ground will, thru the screen voltages changing, affect the amplification factor of the I F and cause quite a change in the I F.
I would monitor the brightness control to ground as I rotate it for a drastic voltage change.

Check the 135V correct?

[Penthode]

So you are saying the VTVM is across R119 and reading off scale on the 5v range? What if you remove the probe ( hot) lead? Does the meter go to zero?

[Penthode]

I checked step 6 and see the problem. The instruction manual has an error. The table gives an incorrect connection of the VTVM to the junction of L104 and R126. You need to measure across R119 with the case of the VTVM at -120vdc.

Please explain because you were talking as if the VTVM was faulty.

[Penthode]

I have an alternative procedure which is safer and more precise. I will follow up once I see your reply. Can't recall seeing the error before but it explains what you are seeing.

[Zenith26kc20]

Check the 135 v as you rotate the brightness control. If it varies widely, suspect a problem with it.

[Chris K]

Ok guys thanks for everything tonight. Gonna get back on this tomorrow morning and I’ll report in and answer all questions

[Penthode]

I may not be available in the morning so here goes. The table measuring at the junction of L104 and R126 is impossible because on my diagram there is no junction.
The reason your VTVM goes off scale is because there is a DC bias of at least 10vdc there.
To adjust the traps do this:
Connect the VTVM to pin 1 of V106 and ground.
Switch the VTVM to the 5vac range. Not DC.
Next switch the HP8601a AM modulation on to 1kHz.
Adjust input RF until you see about 3 volts AC on the VTVM
Adjust the traps null at frequency specified.
Raise the RF level as necessary to keep the null at no less than 1 vac.
Repeat this for each of the trap frequencies.