Sinclair ZX80 / ZX81 Forums

Erm wrote: ↑

Sun Dec 15, 2019 6:27 pm

Mentioned in another recent topic, but I thought I'd share it here so that people can find and add details of early ZX81's.

This one is very early, so I have bragging rights for now .

Sorry, when I started reading this post, I thought it was Lardo with yet another Zeddy

Mark

Lardo Boffin wrote: ↑

Sun Dec 15, 2019 5:29 pm

I quite liked the Sinclair ROM bodge

You mean ‘mandatory modification’ surely

Mark

Presumably the major issue with bent pins on an IC is that it makes maintenance more difficult in the future? Would it be possible to fit a low profile socket, then fit another socket (pins bent out) and put the IC in that? Only the sandwich socket is modified and the RAM chips are easily swappable...

Mark

That’s a nice looking ZX80

In relation to the ROM and EPROMs, check out this useful page

Mark

Thank for the links. I was wondering how using one of these to get 32K would work in relation to your mod process? Presumably the same tracks would be cut. Would the part where you reconnect the two cut tracks be connected directly to a pin on the vLA? https://www.sinclairzxworld.com/download/file....

I've done a few of these (and have done a lot of fiddling with various configurations and written a lot of emails bothering Mr Ingley with silly questions) and there is no need to cut any tracks, just bend out 4 pins (1,2,23,26) of the 32k RAM chip and connect to address lines A11 to A14. Note that...

More help about the vLA81 ZX81 ULA in these threads

The maker describes the vLA81

soft mode changes

I must find time to play with mine some more

Mark

This fault is almost always due to the ULA...

Mark

The difficult factor here is predicting quantity, on small runs the price is X amount, if i order double, it comes down, if i order 5 times the amount, the price comes close to 50% Yeah, I’m aware that the order volume affects the unit cost. Have you posted on the other Sinclair / ZX Spectrum forum...