One thing to watch for on the 1500 is the high value dropper section going o/c. I think it is 1.5 k on early sets and 1.7K on later models
If that section goes o/c the L.T voltage goes sky high and usually takes out most of the transistors excepting the ones in UHF tuner thankfully.
I had a few sets that had suffered that fate, If I refurbed one for re-rent I always fitted a new dropper. They usually had a section or two fitted with 'Polo mints' by then so needed changing anyway really.
I saw a few sets that had a brown line burnt on the tube face due to drys on the frame transformer customers just got used to giving it a thump when the frame collapsed but then there was always the day they left it running unattended...
The 20" Mazda tubes seemed a lot more prone to screen burns than the earlier 19" tubes. I saw quite a few 'game burns' on 20" tubes, one particular make of the Tele tennis game was almost sure to burn goal outlines on the screen if the set was run at high contrast and brightness levels. Maybe the phosphor was thinner or cheaper on later mono tubes?