Sinclair ZX80 / ZX81 / Z88 Forums

Which one? The 16K, the 32K or the 64K? My comment above only applies to the 16K RAM packs. The 16K version uses 4116 (or equivalent) DRAM chips, which require three different supplies, one of which is a +12V DC nominal supply (with a tolerance of +/- 10%). To get the “+12V”, they use the nominal “+...

If you had to take a child to school by road, would you use a gas guzzling posh 4x4 or a fuel efficient modern small car? Floating point numbers are the “jack of all trades” and can cope with a very wide range of numbers. But there are some potential disadvantages. They only store approximations (be...

Thanks for the help. I dont have a ram pack but i will look to see if i can get one cheap, so that i can test with this. When using the ram pack im guessing it ignores the internal memory then? Yes. With an external RAM pack, the internal RAM chip(s) are disabled. So as long as it/they are not shor...

You may find this post useful.

Mark

With the 2114 / 21L14 SRAM chips, there is no need for LK1 or LK2 to be fitted. 21L14 are the lower power versions of the 2114 chip. Each 2114 provides 4 bits. With two 2114 chips, that gives 1K bytes. Either LK1 or LK2 is needed when different SRAM chips are fitted. For example if a single 4118 1K ...

Anything that stops the Z80 CPU from running the system code from ROM will cause a white screen. One common cause of a ZX81 with a white screen is faulty RAM. But a fault with the ROM, the Z80, the ULA or any of the components that link any of these chips can cause the same symptoms. Not applicable ...

Hello and welcome to our forum. The frequency of the signals on the ULA pins 12 and 13 depends on the ratio of RAM to ROM accesses. They don’t operate at specific defined frequencies. Pin 12 is the /RAMCS signal from the ULA to the on board SRAM. Pin 13 is the /ROMCS signal from the ULA to the on bo...

As with most competing devices, each has its pros and cons. And which one is better very much depends on what you want to do with it.

Most owners of 1980s computers are biased (even if only a little bit, including myself) based on what they experienced or owned back in the 1980s.

Mark

I think you may be waiting a long time for any changes to be made...

Maybe a translation site would help...

Mark

For an issue 3 board, I suggest you do the following: Remove: R3 (2.2k), D1 (BA157 or BA221), D2 (1N4002), D4 (12V Zener), D8 (5.1V Zener) and the coil. Remove all the existing 4116 (or equivalent) DRAM chips. Confirm by visual inspection that the only components connected to the former +12V supply ...