ZX81 Enhanced ULA replacement module.

[Andy Rea]

did you open the zx81 ?

has it had the extra 5 address lines connected ?

do other features work like inverted video ?

is it set to zx80 mode ( check the jumpers )

regards Andy

[PokeMon]

One moments, pictures follow.

[PokeMon]

20170106_221326k.jpg (262.18 KiB) Viewed 4530 times

20170106_221338k.jpg (249.91 KiB) Viewed 4530 times

20170106_221346k.jpg (186.01 KiB) Viewed 4530 times

[Andy Rea]

it looks like its right,

very perplexing,

[PokeMon]

I have to say - it is working when leaving the case open.
Strange. Maybe some bad contact ...

[Andy Rea]

oh.... i wonder if the wires near the keyboard connector could have shorted ?

what happened to R16 and R17 ?

[PokeMon]

Not sure if properly installed in general.
Peeking and poking is working now, at least the video features (bit 4, bit 5).
Choosing Turbo mode makes the system hang (128 or 144 in address 101).

[Andy Rea]

it has the sinclair slow rom

have a different rom you could fit ?

[PokeMon]

Nope, no ROM to change. R15, R16 and R17 are soldered to the backside. (220k, 1k, 1k).
Is there a workaround for this ROM or does turbo not work here ?

[PokeMon]

Maybe this is where you have to cut one trace.
I won't do this as this is Paul's ZX81 issue ONE in very good condition.
Holy shit, if he read that I opened it could cause trouble.