Audio waveform on a CRT TV

[UncookedCorn]

I am working on project to transform a CRT TV into an audio waveform display, using a Vintage 1984 Panasonic TRF-438P Desktop Television AM/FM Radio Alarm Clock. The video I’m following is https://youtu.be/bO-DWWFolPw?si=qiyMTYlono_kKcxK and I’m solely following the waveform to CRT instructions. We’re taking the horizontal wires from the TV and plugging them into the tda7297 amplifier, which is being powered by a 12V supply. The issue is that I’m seeing an extremely dim vertical line on the TV when the horizontal wires are disconnected, but the line is a bright horizontal one when the vertical wires are disconnected. No waveform is being displayed when we hook up the amplifier with the horizontal wires, using a 3-wire audio jack to an audio source.
I’m struggling to understand what the issue would be and any help/assistance would be appreciated. Thank you. 

[moffy]

One of the waveforms needs to be a sawtooth sweep with a blanking between each sawtooth and the other can be the signal, but it is very dependent upon the detail. The high voltages around a CRT can be shocking and possibly lethal, and some TVs have a live chassis. Do you have the experience or knowledge to know how to do this safely?

[Ian.M]

In most CRT TVs (and all low voltage ones I have seen) the line scan coils are an integral matched part of the line output circuit which also (via the line output transformer) generates all the high voltage supply rails used for the CRT cathode driver and gun bias, + final anode EHT voltage that actually accelerates the electron beam.  You would need to replace them with a big inductor of about the same (measured) inductance and a saturation current greater than the peak flyback current to keep the voltages the same. Unless you can wind it yourself on a salvaged big ferrite core, it will *NOT* be cheap.

TLDR: CRT TV to scope conversions are difficult and only reasonably practical for selected models that don't use line scan derived EHT.

[Andy Chee]

I have a doorbell camera "flat CRT" waiting for a similar project, so will be seeing how you progress!