connecting to Digital TV

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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Guesser
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Re: connecting to Digital TV

Post by Guesser » Wed Mar 21, 2018 6:19 pm

Ast A. Moore wrote:
Wed Mar 21, 2018 4:49 pm
(primarily, because I’d need to source a male 2.1 mm plug + female socket, and cobble together something of a neat enclosure for them).
Inline socket, with one cable off to the SCART plug and another a couple of inches long to the plug. No extra enclosure required. :)
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Ast A. Moore
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Re: connecting to Digital TV

Post by Ast A. Moore » Wed Mar 21, 2018 6:58 pm

Guesser wrote:
Wed Mar 21, 2018 6:19 pm
Inline socket, with one cable off to the SCART plug and another a couple of inches long to the plug. No extra enclosure required. :)
Hmm. Having trouble visualizing it, but I guess you’re right.
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Re: connecting to Digital TV

Post by denjerus » Wed Mar 21, 2018 7:18 pm

Wow. Thanks for the huge response from all you guys.
I made a the mistake of thinking this would be either a simple "its gone belly up, ditch it" or maybe "Check you've got the plug in properly."
it's been best part of 30 years since I took a plug apart and back then there was 3 cables in it, and a 13 amp fuse! Now there's talk of a pin 20.... where do I get a composit lead to put on pin 20?
I must have given the impression I knew what I was talking about.. My bad!
Is there a chance any of you guys could type slowly how I go about powering this RGB to SCART cable (refered to in the initial slots of this feed) or turning the vertical sync to a composite sync.
or should I seek a computer guy in town to sort it for me?
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Re: connecting to Digital TV

Post by Seven.FFF » Wed Mar 21, 2018 7:55 pm

Definitely! There's a huge breadth of knowledge and diagnostic skills about Spectrum matters out there generally, and on this forum. And pretty much everything is repairable.
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Re: connecting to Digital TV

Post by Seven.FFF » Wed Mar 21, 2018 8:01 pm

Sections 5.2 and 5.3 of this document cover making a powered SCART cable for your 128+.

edit: numbered as the paragraphs are, on pages 7 and 8. Ignore the numbering in the Table of Contents.
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Ast A. Moore
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Re: connecting to Digital TV

Post by Ast A. Moore » Wed Mar 21, 2018 8:53 pm

denjerus wrote:
Wed Mar 21, 2018 7:18 pm
where do I get a composit lead to put on pin 20?
Well, for starters, Robin gave you a link to a pretty good guide. That should give you a general understanding of which signal goes where.

There’s no guarantee that the composite signal is present in the lead at all. It could have been omitted in the wiring altogether. (As I mentioned earlier, it’s not necessary for the RGB signal, so whoever made the cable you have might have used the CSYNC signal instead.) If that is the case, while technically wasteful, it might prove useful in the long run to simply use the existing conductor in the cable and rewire it on the DIN 8 (Spectrum) end from pin 4 to pin 1. On the SCART end, you’ll want to remove the two resistors that form a voltage divider, and replace them with a single series resistor of, I don’t know, 33–47 Ω.

The TL;DR version: we need to connect pin 1 (instead of pin 4) of the DIN 8 plug to pin 20 of the SCART.

Don’t be overwhelmed by the number of conductors in the SCART connector. You’re only interested in about half a dozen of them.
denjerus wrote:
Wed Mar 21, 2018 7:18 pm
should I seek a computer guy in town to sort it for me?
Bah, where’s the fun in that? :D
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Re: connecting to Digital TV

Post by balford » Wed Mar 21, 2018 10:32 pm

You can find details on how to make your 128 Spectrum SCART compliant here (requires a little soldering, well within the reach of a beginner):
https://spectrumforeveryone.com/technic ... compliant/
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Re: connecting to Digital TV

Post by Guesser » Thu Mar 22, 2018 12:03 am

Ast A. Moore wrote:
Wed Mar 21, 2018 4:49 pm
Guesser wrote:
Wed Mar 21, 2018 3:40 pm
The 128 only provides separate horizontal and vertical syncs.
Oh, sorry, I misspoke. I meant composite sync, not vertical sync. But since the composite sync is already present in the full composite signal, I decided to go with the latter.
It's my fault, I was talking rubbish and confusing the issue again. The 128 has VSYNC and CSYNC, I was muddling it up with monitors with VSYNC and HSYNC. :oops:
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Re: connecting to Digital TV

Post by Guesser » Thu Mar 22, 2018 12:08 am

balford wrote:
Wed Mar 21, 2018 10:32 pm
You can find details on how to make your 128 Spectrum SCART compliant here (requires a little soldering, well within the reach of a beginner):
https://spectrumforeveryone.com/technic ... compliant/
I feel like that article misses a trick by not also describing the mods to put audio on pin 3 and the second 12V on pin 5. One SCART cable pinout to rule them all (and fully support all the SCART signals) :)

I suppose they're somewhat more involved on the 128, needing wire to patch signals across.
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Ast A. Moore
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Re: connecting to Digital TV

Post by Ast A. Moore » Thu Mar 22, 2018 9:19 am

Guesser wrote:
Thu Mar 22, 2018 12:03 am
It's my fault, I was talking rubbish and confusing the issue again. The 128 has VSYNC and CSYNC, I was muddling it up with monitors with VSYNC and HSYNC. :oops:
No worries, mate. I knew exactly what you meant.
Guesser wrote:
Thu Mar 22, 2018 12:08 am
I feel like that article misses a trick by not also describing the mods to put audio on pin 3 and the second 12V on pin 5. One SCART cable pinout to rule them all (and fully support all the SCART signals) :)
I suppose they're somewhat more involved on the 128, needing wire to patch signals across.
When I got the Toast Rack, I was briefly tempted to stuff the brightness mixing circuitry inside the machine and rewire the socket to match a +2A/+3 so I could use the same cable for both machines. (Besides, I didn’t have any more DIN 8 plugs on hand.) It just felt . . . wrong, so I made a separate cable. I did try to match the signal levels between the machines, which took several tries and combinations of resistors in the voltage dividers. The kitchen walls resounded with many a strong word that day.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.

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