Search found 3243 matches

by 1024MAK
Fri Nov 27, 2020 12:58 am
Forum: Development
Topic: ZX21: CERAMIC RESONATOR
Replies: 4
Views: 78

Re: ZX21: CERAMIC RESONATOR

fordp2002 wrote: Thu Nov 26, 2020 11:06 am I am puzzled as to how the ceramic resonator is wired on the ZX81?

It seems to only show two terminals but the device has three terminals?
The middle (centre) pin is connected to 0V/GND, one of the outer pins connects to C6, the other outer pin is not connected to anything.

Mark
by 1024MAK
Wed Nov 25, 2020 5:54 pm
Forum: Development
Topic: ZX21 Project ZX81 Replacement PCB
Replies: 14
Views: 210

Re: ZX21 Project ZX81 Replacement PCB

Hi Ford Hopefully these are constructive comments: TR2 - the transistor used has to have a very quick switch off time. Most general purpose transistors take a small amount of time to turn off, especially if the base becomes saturated. If a BC548 is used the value of R6 may need to be adjusted. If th...
by 1024MAK
Mon Nov 23, 2020 10:26 pm
Forum: Hardware
Topic: Fixing inherited Sinclair ZX81
Replies: 30
Views: 871

Re: Fixing inherited Sinclair ZX81

I use Recom types (because I bought a load when the price was low), as detailed (and shown) in this topic. But other similar types like from Traco Power and MuRata are fine as well.

Mark
by 1024MAK
Mon Nov 23, 2020 7:15 pm
Forum: Hardware
Topic: Fixing inherited Sinclair ZX81
Replies: 30
Views: 871

Re: Fixing inherited Sinclair ZX81

That’s good news :D

Mark
by 1024MAK
Mon Nov 23, 2020 7:12 pm
Forum: ZX Spectrum Lounge
Topic: 128k +2 Mysterious Videos issue.
Replies: 36
Views: 7524

Re: 128k +2 Mysterious Videos issue.

Good to hear that you are up and running :D

Mark
by 1024MAK
Mon Nov 23, 2020 1:38 pm
Forum: ZX Spectrum Lounge
Topic: 128k +2 Mysterious Videos issue.
Replies: 36
Views: 7524

Re: 128k +2 Mysterious Videos issue.

Although it is a different version DRAM chip, this datasheet has useful English descriptions of the various control signals and access cycles. I need to point out that there are two types of 4164 DRAM chips, those with 7 bit/128 cycle and those with 8 bit/256 cycle refresh. Z80 systems normally use ...
by 1024MAK
Mon Nov 23, 2020 1:33 pm
Forum: ZX Spectrum Lounge
Topic: 128k +2 Mysterious Videos issue.
Replies: 36
Views: 7524

Re: 128k +2 Mysterious Videos issue.

The multiplexer for all the DRAM chips is IC10 (which goes by one of these part numbers depending on when it was made: PCF1306P, ZX8401, 40058). Unfortunately new chips are very rare now. But there are PCB modules that perform the same function. To make sense of the signals going to/from the DRAM, y...
by 1024MAK
Mon Nov 23, 2020 1:37 am
Forum: Development
Topic: ZX81 Clone Tynemouth Minstrel 3
Replies: 45
Views: 21563

Re: ZX81 Clone Tynemouth Minstrel 3

👍 :D

Mark
by 1024MAK
Mon Nov 23, 2020 12:12 am
Forum: ZX Spectrum Lounge
Topic: 128k +2 Mysterious Videos issue.
Replies: 36
Views: 7524

Re: 128k +2 Mysterious Videos issue.

Yes, I was going to say, to run a diagnostic ROM. But you must have read my mind :shock:

If diagnostics are at least running, then the Z80 is mostly working. The ULA is also mostly working. It could be one of the chips that multiplexes the address lines to one of the groups of DRAM chips.

Mark
by 1024MAK
Sun Nov 22, 2020 9:55 pm
Forum: ZX Spectrum Lounge
Topic: 128k +2 Mysterious Videos issue.
Replies: 36
Views: 7524

Re: 128k +2 Mysterious Videos issue.

Can you burn EPROM chips?

Mark