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Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 10:55 pm
by Andy Rea
McKlaud wrote:
Tue Mar 13, 2018 10:46 pm
Has anyone got any schematic diagram or datasheet of the UM1233 modulator? I would appreciate if you could share it, please.
this may be of use... liberal use of google translate may be needed...

http://www.ep128.hu/Sp_Hardware/SP_Modulator.htm

EDIT: i can't find the webpage now but... i have it wrote down voltages for the modulator should be approx...

2.55v sync, 2.85v black / porch and 3.3v full white ( note not quite 1v p - p ) howevere good enough to still give a good signal when fed into a composite input ( may need dc blocking capacitor, depends on your monitor )

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 11:17 pm
by McKlaud
Thanks Andy. I did more searching in a few places including forgotten folders on my hard drive and I've found it. :geek:

Re: do we still use UHF modulators ?

Posted: Tue Mar 13, 2018 11:39 pm
by Andy Rea
Thanks for the PDF's now i have some definitive voltages to work with, the ones i had weren't that far off :lol:

Andy

Re: do we still use UHF modulators ?

Posted: Wed Mar 14, 2018 2:14 am
by RetroTechie
Looks like close to standard composite voltage levels the modulator wants, apart from a DC bias (say, series capacitor or so?). Sadly there's no info on typical input impedance for that modulator. :?:
Lardo Boffin wrote:it does mean that broken zeddies which are not comp modded won’t be fixable with this ULA (..)
Quite possible a replacement ULA could easily provide a good signal for the modulator. Perhaps both that and composite out. Thing is, with my ULA I never even tried...

Why not? For any ZX81 in unknown condition (with Sinclair ULA), a composite mod would be among (my) first actions, because it takes the modulator out of the equation. If the modulator was broken, then that's a fix using a transistor, resistor & capacitor. If it wasn't broken: picture output improved. Regardless of condition of the rest of the machine: win-win. :D

In case of repair with a replacement ULA, the only mod needed is to wire the modulator's input directly to the RCA connector. Even easier than the composite mod.

And for "keep as original as possible" purists: when you replace the ULA with a CPLD based non-Sinclair part, then fuzzing over a wire mod inside the modulator can is kind of silly. Make it easy to reverse in case you'd ever consider putting a Sinclair ULA back in. Not to mention 'needing' a VHF/UHF output in the year 2018. :lol:

Re: do we still use UHF modulators ?

Posted: Mon Mar 19, 2018 10:48 pm
by PokeMon
I have two new modulators here just for the case or maybe I got a collector over the time. 8-) :mrgreen:
Composite is sufficient and if needed I can upshift the signal myself.

Re: do we still use UHF modulators ?

Posted: Mon Mar 19, 2018 10:57 pm
by McKlaud
PokeMon wrote:
Mon Mar 19, 2018 10:48 pm
I have two new modulators here just for the case or maybe I got a collector over the time. 8-) :mrgreen:
:mrgreen: if you did wait another 37years, yes definitely it would be worth a fortune in "Antique Roadshow" :mrgreen:

Re: do we still use UHF modulators ?

Posted: Mon Mar 19, 2018 11:10 pm
by krowne
Absolutely no point in catering for CRT for me it's LCD all the way.
Brian

Re: do we still use UHF modulators ?

Posted: Tue Mar 20, 2018 7:36 am
by BarryN
Most TVs still support an analog RF signal, and I use use an old black and white TV on VHF with my Timex Sinclair 1000. Anyway, it would be nice for a replacement ULA to be a drop in replacement and not require any other modifications.