ZX Spectrum +2 Grey video artifacts

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX Spectrum +2 Grey video artifacts

Post by 1024MAK » Thu May 04, 2017 6:53 pm

I'll have a look at the video, and study your earlier post with the SCART lead details tomorrow when I've got a day off work.

Mark

repetto74
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Joined: Tue Dec 20, 2016 7:46 pm

Re: ZX Spectrum +2 Grey video artifacts

Post by repetto74 » Thu May 04, 2017 7:01 pm

Hi 1024MAK

Many thanks to you 😄

Rick

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: ZX Spectrum +2 Grey video artifacts

Post by 1024MAK » Sun May 07, 2017 12:07 pm

Hi Rick

So the SCART cable looks okay. But see the notes below.

My analysis is this:

Code: Select all

DIN LEAD --------------------- SCART PIN - SCART Function / Notes

Pin 1 --> grey wire -----------> pin 8 --- Switching (need +5V to +8V for on @ 16:9 or +9.5V to +12V for on @ 4:3)
Pin 2 --> black wire ----------> pin 13 -- 0V/GND (RGB video ground)
                     ----------> pin 18 -- 0V/GND (Blanking ground)
Pin 3 --> white/purple wires --> pin 2 --- Audio, right channel
                             --> pin 6 --- Audio, left channel
Pin 4 --> brown wire ----------> pin 20 -- Composite sync (75 ohm input)
Pin 5 --> yellow wire ---------> pin 16 -- Blanking (need +1V to +3V to select RGB mode)(75 ohm input)
Pin 6 --> green wire ----------> pin 11 -- Green video (75 ohm input)
Pin 7 --> red wire ------------> pin 15 -- Red video (75 ohm input)
Pin 8 --> blue wire -----------> pin 7 --- Blue video (75 ohm input)

There is a purple wire bridge on the SCART between pins 2 and 6 (2 is shared with the white wire).
There is also a purple wire bridge between pins 18 and 13 (13 is shared with the black wire).

French +2 DIN socket functions
==============================
Pin 1 - +12V via a 1k resistor (LK2 fitted, LK4 NOT fitted)
Pin 2 - 0V / GND
Pin 3 - Audio/sound out  (LK8 fitted, LK7 NOT fitted)
Pin 4 - Composite Sync
Pin 5 - +12V via a 1k resistor (LK3 fitted, LK1 NOT fitted)
Pin 6 - Green video (via a 75 ohm resistor)
Pin 7 - Red video (via a 75 ohm resistor)
Pin 8 - Blue video (via a 75 ohm resistor)
It looks like you got confused by the DIN connector pin numbering (you mirrored the numbers, don't worry, it is easy to do). So in the details above, I have corrected this to what I think it should be.

Note that the French +2 grey has a completely different signal allocation on the RGB/Video socket compared to U.K. models. So this SCART lead can only be used with French +2 computers.

Depending on how closely your TV follows the SCART "standard", the control voltage on the SCART Blanking input (pin 16) may be a little bit to low for it. It is suppose to be between +1V and +3V to select RGB mode. But the +12V from the Spectrum is limited by a resistor, so the voltage at SCART pin 16 may only be 0.83V. But as you have a colour picture, this may not be the problem here.

More later...

Mark

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1024MAK
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Re: ZX Spectrum +2 Grey video artifacts

Post by 1024MAK » Sun May 07, 2017 12:30 pm

Rick

Can you either check your +2 on another TV (an older small screen CRT preferred), and / or see if the TV you have been using has either a remote control button, or an on screen menu setting to select RGB mode. This can be called a number of different things, so you may need to read the instruction booklet.

SCART sockets can carry one of upto four different types of video signal:-
  • Composite video
  • RGB video
  • S-video
  • Component video
Not all TVs support all these, the minimum being Composite video, with some supporting RGB video (either manual selection by the user, automatic via the SCART control signals, or automatic with manual override).
It is the RGB mode with manual override that you want. Sometimes known as AV input selection.

Next question: can you solder?
And are you in the U.K.?

Mark

repetto74
Posts: 43
Joined: Tue Dec 20, 2016 7:46 pm

Re: ZX Spectrum +2 Grey video artifacts

Post by repetto74 » Tue May 09, 2017 3:52 pm

Hi 1024Mak

I will do as you requested and check 8-) Actually I am travelling abroad for the whole week and cannot test the machine. I will revert to you beginning of next week with the results ☺️
And yes I can solder and have all needed tools to repair electronics. I am located in Belgium 😉

Thanks
Rick

repetto74
Posts: 43
Joined: Tue Dec 20, 2016 7:46 pm

Re: ZX Spectrum +2 Grey video artifacts

Post by repetto74 » Tue May 16, 2017 6:28 pm

Hi 1024mak,

Finally back home ! :-) I have checked the possibility to test on another scart monitor but unfortunately at the present moment I do not have this option. The led TV I am using is quiet new (1 year old, HAIER brand) and I do not see in settings any possibility to manually switch the scart to the RGB mode so I do assume that this is autoswitching.

I have noted that the grey glitches which pops up and rolls fast from top to bottom are only visible with a white and yellow background :?: I ran the test mode of the machine and as you can see on the picture when you zoom it up, the grey patterns are only populating white and yellow areas of the color test page.

I can anyway live with that, I think probably there is something wrong with the video circuitry or maybe a bad soldering on the scart connections. I think now that this scart cable is the one for the french Spectrum 128k +2 otherwise I would have had probably no video at all.
It may also be that the video signal needs to be amplified somewhere. Are there some resistors to be supposed being part of the scart cable for the French version ?? :?:

What I am trying now is to have the DIVMMCx2 to work with the machine as posted on another thread :?
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