Sinclair ZX80 / ZX81 / Z88 Forums

Internal RAM mod and empty case is not authentic hardware solution, it's not like in 80s. As for me is better to tried save original hardware, because in other case is emulator enough.

Line 140 - loop from 0 to 120 and it is X coordinates, which you use in PLOT at the line 141, but X can be from 0 to 63, no more. Same mistake at the line 146 & 151 - you tried to PLOT at the coordinates 100,100 and by this you got B mistake at the line 151. And please check all your loops. For exam...

For repairing old computers, as a hobby, I use really simple oscilloscope Fnirsi - 2031H with price less than $50. Yes, it's look as baby's toy, but for old hardware with low frequencies it's can be useful.

My solution is more simple - a piece of double sided scotch between RAM pack and ZX81, above of connector. You know - scotch can solve many problem in our life and it's one of such case.