What could Account for This? RCA 9TC-240 Power Issue

[bandersen]

Originally Posted by Chris K

So if I understand what has been described earlier in the thread, if the switch is moved to the phono position, the TV brightness control ground is interrupted and the screen goes dark. There's still HV however. The sound circuit then comes out of pin 5 of the 6AL5 discriminator as coaxial to the switch where it picks up audio input from the RCA jack and is brought back into the sound circuit as a grounded coax line. Around there I get lost! To me it seems the signal goes to terminal 3 of the volume control and out of terminal 2 as coax to pin 1 of the 6AV6 bias clamp???

Yes, pretty much. They way the drew the switch is a little confusing. The switch element go left/right not up/down.

* Ground lug 3 of the brightness control.

* Connect the two ends of the coax together so that the end of R215 is going to C184.

[Chris K]

Originally Posted by bandersen

Yes, pretty much. They way the drew the switch is a little confusing. The switch element go left/right not up/down.

* Ground lug 3 of the brightness control.

* Connect the two ends of the coax together so that the end of R215 is going to C184.

That's what I thought looking at it. So all the capacitor and coaxial stuff going on around the volume control, all of that stays in place? That's where I got lost!?

[Chris K]

I guess all that stays there. Just do the coax link at the level of the tube bottoms in the chassis

[Chris K]

...and my "Noobieness" exposed...how are these pot terminals numbered again? Are they depicted from the back, non shaft side of the pot? What is that fourth terminal coming out the side of the volume pot?

[Chris K]

Once I get sound and a decent picture on the 10BP4, I'd like to do a basic alignment on the sound and video IF circuits just to make certain everything is OK and for my own experience. I've never been able to do one successfully before. Bob, I watched your recent video doing the sound align and all of the changes small movement of the adjustment coils made in the symmetry of the traces. I certainly don't have your HP monster on my bench but I do have an Eico 369 sweep generator that can do the 20-25 mc frequencies needed. I also have a decent HP scope from the mid 1980s. I'll probably start it as a separate thread. Your alignment series on YouTube was very informative but there were some Noob things I didn't understand so as I start that process, I'll be asking the choir for their help and guidance.

[bandersen]

I suggest just tracing out the wiring on the pots. 4th terminal would be for tailoring the response of the sound. You could boost low or high end for example. Sometimes called a "loudness" tap.

[Yamamaya42]

Originally Posted by bandersen

I suggest just tracing out the wiring on the pots. 4th terminal would be for tailoring the response of the sound. You could boost low or high end for example. Sometimes called a "loudness" tap.

Turn it up to 11!
I have an eico 324 signal generator myself, problem is with these, w/o a frequency counter it's hard to know if they are putting out the frequency you want or how well they are calibrated, not that you need to be THAT precise when you align, but i did mess up the first few times i tried, then got a digital unit and got it pretty good on my 4th try on my Arvin.

I too will be watching the Alignment progress, As my FADA needs work and is much harder than the Arvin!

[Chris K]

I don’t have a frequency counter but I’ve been dialing in the RF output using my scope. It does jump around a little but never more than half a megacycle. Last night I checked it trying to get 20.5 of and it bounced around between 20.3 and 20.7 mc. It that too much inaccuracy?

[Yamamaya42]

Originally Posted by Chris K

I don’t have a frequency counter but I’ve been dialing in the RF output using my scope. It does jump around a little but never more than half a megacycle. Last night I checked it trying to get 20.5 of and it bounced around between 20.3 and 20.7 mc. It that too much inaccuracy?

Not sure about that, I just know I failed with my attempts with the analog one till I got the much more costly digital unit.
Yours may be OK.
https://www.amazon.com/Generator-Pre.../dp/B07H8BM2FM

I did not spend that much when I got it 3 years ago! :O

[Chris K]

Supposedly the 369 is supposed to be good for this kind of sweep generator stuff but since I’ve never used it successfully who knows. There’s a respected ebayer who makes replacement rf output and demodulator input cables for it and I got them. The scope output is a strange output style though and to be “NoobHonest” I have no idea how to hook this output to my scope. They show X-Y connections and say to use your scope in X-Y mode etc and that’s where my head starts to spin. Frankly my scope experience is hooking the probe to a test point and ground, pushing Autoscale and comparing the trace to a photo. That’s about it.

[bandersen]

That frequency is jumping around too much. Foe example the sound needs to be at 21.25MHz so you'll want something stable to at least two decimal places.

Eico scope output is three leads - ground, vertical (Y) and horizontal (X). Eico cable ends with three alligator clips as I recall. Do you have it?

What scope do you have? Needs to be a two channel capable of XY mode. That simply means the electron beam is moved entirely by whatever signals are coming in on the X and Y. Turns you scope into a vector monitor.

For that matter you can use a vector monitor instead of a scope if you have one. Like the Tek 604 or Wavetek 1901

[Chris K]

Which way do you look at these controls to read the numbers? The flat back side or the front shaft side?



Sorry about that!

[kvflyer]

Yikes!

[bandersen]

I don't know that there is any strict convention for control lug numbering. That's why I suggested you follow the wiring.

[Chris K]

I did trace it out and it is all wired correctly...but still no sound so I'm going to need to start tracing backwards through the audio circuit. Before I had some pops and cracks when I moved tubes around but now the speaker is silent...and it was before I did the re-wiring work. Also, somewhere along the line, someone replaced the 6AG5 converter and RF amp in the tuner with two 6BC5 tubes. There doesn't seem to be too much of a difference in performance when I went back to the 6AG5s.