Search found 2117 matches

by 1024MAK
Thu Nov 15, 2018 9:03 am
Forum: Hardware
Topic: Vertical Bars on Power Up / Solution
Replies: 2
Views: 60

Re: Vertical Bars on Power Up / Solution

The ZX Spectrum 16k, 48k and Plus models all have a DC/DC converter/inverter power system on the main board to generate +12V and a -5V supply rails for the 4116 DRAM chips. The +12V is also used by the colour encoder chip (LM1889). Models using unmodified issue 1,unmodified issue 2, some issue 3 (un...
by 1024MAK
Wed Nov 14, 2018 10:24 am
Forum: Sinclair Misc
Topic: Should i move to Europe to acquire a ZX81?
Replies: 5
Views: 104

Re: Should i move to Europe to acquire a ZX81?

The ZX81 for sale in this thread is priced at £30.95 (plus postage). Using the exchange rate that Google uses gives a price of $40.11 USD (not including postage). Typical prices are around £20 to £40 for ZX81’s that are ‘untested’. Here is a link to eBay.co.uk showing actual selling prices. As you c...
by 1024MAK
Wed Nov 14, 2018 10:14 am
Forum: Hardware
Topic: TS1000 ULA vs ZX81 ULA
Replies: 24
Views: 1066

Re: TS1000 ULA vs ZX81 ULA

(Glad I could flip the switch without power cycling and re-typing. It was only like a 6 line program, but still. ;-) ) And it looks like my switch worked! Yay! ;-) Yes, the Sinclair ROM code reads the 50/60Hz pin every time it generates a TV line. So if a switch is connected to this pin, you can sw...
by 1024MAK
Wed Nov 14, 2018 10:07 am
Forum: Hardware
Topic: Why was Sinclair selling UK model ZX81s in the USA?
Replies: 9
Views: 475

Re: Why was Sinclair selling UK model ZX81s in the USA?

893B2F76-B2C3-4241-A505-4069DF9B237C.jpeg BAC0334D-255C-4FCA-8A60-7E5FECD9BC8D.jpeg F586C1E8-496B-437F-A42B-C65039B7243C.jpeg BDFBF906-F15C-4507-B27F-28B1E25D4388.jpeg As you can see, the marks show up more on some cases, and on others are rather hard to see unless you catch the light the right way.
by 1024MAK
Mon Nov 12, 2018 1:55 pm
Forum: Hardware
Topic: Starting Composite Mod
Replies: 8
Views: 209

Re: Starting Composite Mod

Good work on getting your Zeddie working :D :D :D The Sinclair 16k RAM packs are not very reliable these days. The chips used (4116 type 16k bit DRAM types or equivalents) need three supply voltages (+5V, +12V and -5V). Two of these are generated by a simple DC/DC converter/inverter circuit. The ele...
by 1024MAK
Sun Nov 11, 2018 1:22 am
Forum: Hardware
Topic: Starting Composite Mod
Replies: 8
Views: 209

Re: Starting Composite Mod

As far as composite video modifications go, have a look at this thread and the threads that it links to ;-)

Mark
by 1024MAK
Sun Nov 11, 2018 1:14 am
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 26374

Re: ZX81 ULA-in-a-CPLD

ZX81 ROM disassembly/ recreated source code available here ;)

Mark
by 1024MAK
Sun Nov 11, 2018 1:03 am
Forum: Hardware
Topic: Starting Composite Mod
Replies: 8
Views: 209

Re: Starting Composite Mod

What cell or cells (battery) does your multimeter use? Semiconductor junctions may turn on and conduct when the voltage across them is around 0.6V or higher. There are transistors in the modulator. And in the ULA chip. To carry out continuity testing without the semiconductor junctions messing up th...
by 1024MAK
Sun Nov 11, 2018 12:54 am
Forum: Hardware
Topic: ROM cartridge
Replies: 3
Views: 120

Re: ROM cartridge

Timex Sinclair released TS1510 expansion for TS1500, TS1000 and ZX81, to use ROM cartridges. The Chrome interface has a cartridge port as well. This is compatible with the Spectrum ZX Interface 2. Does anyone know if these cartridge interfaces are compatible? The two different cartridges are comple...
by 1024MAK
Sat Nov 10, 2018 3:31 pm
Forum: Development
Topic: ZX81 ULA-in-a-CPLD
Replies: 233
Views: 26374

Re: ZX81 ULA-in-a-CPLD

McKlaud wrote:
Sat Nov 10, 2018 2:56 pm
Mark,

Thanks for ideas, but I've tried my ULA it two different board. One was fitted with newer 27C64 chip with programmed the latest ROM. The same issues on both PCBs.
Well then, at least that may be something that’s eliminated.

Mark