Sinclair ZX80 / ZX81 / Z88 Forums

What about Z80SRAM - RAM / CPU module suitable for Sinclair ZX Spectrum 48k here.
Would it work on a TC2048?

landex wrote: ↑Mon Jun 06, 2022 8:38 pm Would it work on a TC2048?

Although I don't know for sure, because the TC2048 differs internally from a Spectrum 48K I wouldn't have thought that the CPU would work with the 32K upper ram enabled, but it might do CPU only.

I just noticed that my TC2048 has 2 41464 (not 4164) chips in addition to the 4416 chips.

I've desoldered my ram chips and tested them with a dram tester I bought from eBay, unless you can desolder or get a lot of desoldering practice on something unimportant, you'll have to get a repair.

Have you got a better picture of the component I mentioned on your motherboard that looks burnt out in the picture you posted?

landex wrote: ↑Mon Jun 06, 2022 8:38 pm What about Z80SRAM - RAM / CPU module suitable for Sinclair ZX Spectrum 48k here.
Would it work on a TC2048?

I would be very careful with this. In a Sinclair ZX Spectrum 16K/48K/+ the ‘upper’ 32k bytes of RAM has its own control circuit. Hence it is easy to use a module like that which you linked to. All you do is to remove the ‘upper’ DRAM chips (which are obviously not fitted in a 16K model).

However, the TC2048 is a development from another computer, hence it’s hardware is significantly different. It uses a gate array to control its memory not a ULA(s) and 74LSxxx logic chips like the Sinclair ZX Spectrum 16K/48K/+.

Mark

1024MAK wrote: ↑Wed Jun 08, 2022 5:22 pm
However, the TC2048 is a development from another computer, hence it’s hardware is significantly different. It uses a gate array to control its memory

Mark

Which chip is a gate array can I ask, Mark?

sP1d3r wrote: ↑Wed Jun 08, 2022 7:29 pm

1024MAK wrote: ↑Wed Jun 08, 2022 5:22 pm
However, the TC2048 is a development from another computer, hence it’s hardware is significantly different. It uses a gate array to control its memory

Mark

Which chip is a gate array can I ask, Mark?

U2, the SCLD chip. It does the functions that the ULA does in a ZX Spectrum, but also controls ALL the DRAM chips. Hence each DRAM chip having its /CAS control line fed from U2.

If you want to fit a module that has RAM included on the same module as the Z80A microprocessor, then the equivalent of the ‘upper’ RAM on the TC2048 would definitely have to be removed or disabled.

I don’t recommend someone trying to desolder chips from a PCB unless they are very experienced at this task. As the likelihood of the PCB tracks being damaged is high.

Now if by using the BASIC test programs, it can be worked out which DRAM chip is faulty, that bad chip can be cut out. Then the individual pins carefully removed. A IC socket can then be fitted. Suitable replacement DRAM chips are likely still available on the likes of eBay. And cost considerably less than the cost of the module that was linked to.

Alternatively, if the owner prefers, send the computer to a professional repairer.

Mark

1024MAK wrote: ↑Thu Jun 09, 2022 11:48 am
U2, the SCLD chip. It does the functions that the ULA does in a ZX Spectrum, but also controls ALL the DRAM chips. Hence each DRAM chip having its /CAS control line fed from U2.

Thanks Mark, I recently saw a 'homebrew' kit of chips for a Timex 2068 that had an FPGA as the SCLD and wondered how the kit would be built.

I bought by mistake tesla MH84164 DIP16 for the 4264-12 dip18 dram. Then I realize I need dip19!!
Which can substitute the 4264-12 dip18 dram?
IC 4416 I see

landex wrote: ↑Mon Jun 06, 2022 8:38 pm What about Z80SRAM - RAM / CPU module suitable for Sinclair ZX Spectrum 48k here.
Would it work on a TC2048?

I bought it, and it works very good!

landex wrote: ↑Mon Jun 27, 2022 6:27 pm I bought it, and it works very good!

Do you mean that your TC2048 now has 48K of ram?

The latest and most accurate schematic of Timex Computer 2048, PCB rev 5 attached.