Re: My first foray into Old model TV repairs.
This is a really curious condition. At first read through of this thread the raster distortion would probably be attributed to scan coil leakage line/field and vice versa. However, the fact that it goes bad again if the brightness is left low with the set switched on rather knocks that on the head as the coils will be warmed through.
With EHT of 14/15 kV, the beam should be pretty stiff - it's not some old 6 kV soft as putty situation and one starts to think about EHT smoothing due to poor aquadag, as has been surmised. However, if it's there and connected, can it be that bad?
If it was in my workshop, I'd hook up my stabilised EHT PSU instead of the internal supply. That would prove whether the EHT is constant and fit for purpose. Without access to an external lab EHT unit it's down to elimination and the EY51 might be on my hit list as a starter.
Does the image breathe badly with increasing contrast/brightness? That's a clue about the integrity of the EHT supply.
Reading back to the very beginning of this thread, I note the scratch on the CRT neck. I've known cases where such damage hasn't been enough to cause catastrophic failure, but enough to admit very, very small quantities of air which then cause havoc in all sorts of weird ways.
An interesting problem and back to the physics of CRT technology.
Great job so far!
Best regards,
Paul M
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