this article for more info. The easier option is just to ignore half of the chip and get 16K RAM. That is fine because most of the software is designed for 16K.
K. So far so good. The usual test is to run
- PRINT PEEK 16388+256*PEEK 16389
UPDATE: I can now offer a fitting service if you have a ZX81 that needs an internal RAM update, or composite video modification, voltage regulator switch mode replacement etc. Contact me if you are interested.
UPDATE 2: Some more photos, this is the memory size check: