1024MAK wrote: ↑Sat Oct 19, 2019 12:41 pm
bola_dor wrote: ↑Sat Oct 19, 2019 1:45 am
I don't think back porch is missing.. actually I had a clear image with the RF modulator and now I kind of regret about modifying it to the single transistor + resistor arrangement.. image now is sharper but I have this problem I think is something about Sync..
I saw your circuit schematic, as I don't know much about electronics (just copy and solder) would any 100uf 16v capacitor work?
I also I don't think the back porch is missing. As far as I am aware, most TS1000 machines use the later ULA that produces a back porch. But I thought it was worth mentioning just in case.
Any 100uF 16V electrolytic capacitor should be fine. But it is important to connect it with the correct polarity. The value is not critical, the circuit should work with a 47uF 16V type as well.
As these computers don’t produce colour, PAL and NTSC standards are in theory irrelevant, as they are colour TV encoding standards. CCIR 625/50 and EIA 525/60 (line count and field rate) are the proper names for the monochrome baseband (composite) video standards. Alternatively the ITU standards can be used, for example the monochrome U.K. TV standard is System I, that’s 625 line, 15625Hz/50Hz. However, the options shown on screen (if relevant) and in the user manual / instructions of TV and other consumer video equipment often use PAL, PAL 60, NTSC or similar. Sometimes they use PAL I, PAL B/G etc. More information
here and
here.
And of course, most people outside of TV engineering often just use PAL to mean any 625/50 system and NTSC to mean any 525/60 system.
As far as using these computers is concerned, the USA models of ZX80, ZX81, TS1000 etc should work with TVs capable of showing 525/60 (which is normally NTSC) video.
The European (U.K., Germany etc) versions (ZX80, ZX81) should work with TVs capable of showing 625/50 (which is normally PAL) video.
With the ZX81 / TS1000 / CZ1000, the only differences on the board that is relevant to the video system are:
- R30 (10Ω) is fitted to select 525/60 (and hence this resistor is often called “USA”) but left off for European boards (the ULA pin is called USA/UK). Where a TS1000 has found its way into Europe, you often find someone has removed R30...
- Different modulators are used, and the connections are different
- French ZX81 models have some extra components as they use a different video system.
So if you can get a stable display when using BASIC, I find it strange that your TV loses lock when playing games that you are sure worked fine when you used the RF output. One point that may be worthwhile mentioning is this: some TVs support more TV standards when receiving via RF than they do when connected via a direct composite video connection.
I do think it is worthwhile trying a ZX8-CCB. The output from this should be a better signal (closer to the correct voltage levels) than you get from a simple transistor buffer.
Mark
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