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BBC B - Screen vertical rolling & position issues

Posted: Tue Aug 18, 2020 3:19 pm
by nickm
Hi all

I've bought a BBC B from eBay, and hooked it up to a TV via an RGB to SCART lead (from Retro Computer Shack), but have issues with the vertical position of the screen and vertical rolling.

On power up, the top of the screen will be at a random vertical position. The vertical position changes when the machine is powered off and on again. All screen modes exhibit the same issue. When in BASIC, the screen is static and not rolling.

On running most games (eg Codename Droid, Exile) the screen rolls upwards vertically.

There's also some slight horizontal distortion of characters, on power on, but this settles after a second or so.

I've noticed that the 6845 runs quite hot, almost too hot to hold a finger on after a while. Is this normal? The issue occurs on turning on from cold however.

I've recapped the PSU, the screen issue existed prior to this. I have a TurboSPI board plugged into the user port, but no other peripherals connected.

Any assistance gratefully received!