Spectrum +2 Dark RGB

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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Morpheus
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Spectrum +2 Dark RGB

Post by Morpheus » Sat Jul 27, 2019 2:26 pm

Hi
Just picked up a new Grey+2 and have a new RGB Cable for 128/+2 Machines. Problem I have is the Output is very,very dark almost black. I can just make out the Menu screen for the 128 and can hear the menu bar moving.
Do i need to move Link 1 ( TTL ) to Link 3 ( 12v via 1K )

I have a +2B that was doing the same thing and it was something to do with R44 and the Blanking signal. Which got resolved in the end.
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Ast A. Moore
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore » Sat Jul 27, 2019 3:21 pm

Then it’s probably the wrong cable for the +2. The +2 (unlike the +2A) can use two different video output configurations, set via several removable links on the PCB. The two configurations are referred to as Standard and Peritel. If you don’t wish to make or buy a separate cable for your +2, you could configure it to match the video output of your +2A and use the same cable for both machines. I believe the pinout should be identical then.

Note, you will still need to lower the value of R9 to something closer to 470 Ohms.
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Re: Spectrum +2 Dark RGB

Post by 1024MAK » Sat Jul 27, 2019 5:34 pm

Or your TV is in composite SCART mode instead of RGB SCART mode.

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Re: Spectrum +2 Dark RGB

Post by zxplusplus » Sat Jul 27, 2019 6:36 pm

A friend of mine had this problem, it was a blown transistor, i'm not 100% sure which one off the top of my head but TR9 rings a bell.

If you've got a multimeter you can check the transistors yourself :-)
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Re: Spectrum +2 Dark RGB

Post by 1024MAK » Sat Jul 27, 2019 11:54 pm

Some +2 boards had three transistors fitted the wrong way round! One of which affected the signals on the RGB/Monitor socket. See this thread (Correction of +2 hardware errors) over on World of Spectrum ;-)

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Morpheus
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Re: Spectrum +2 Dark RGB

Post by Morpheus » Sun Jul 28, 2019 7:27 am

The cable I bought is a proper 128/+2 Cable and Pin 1 was set as Pin 16 ( Blanking ) on the SCART end. The +2 had Link 4 set which made Pin 1 CVBS. I fitted a 470R Resisitor to R9 ( which was empty ) and set the link to 2 so Pin 1 would be 12V to the Pin 16 Blanking. It still cannot switch it into RGB though. Do i need to fit a jumper wire to Pin 8 of the SCART ( Funtion Switching )? In the meantime i'll check the transistors. The last +2 didn't have the problems this has and the Cable and TV haven't changed.
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Ast A. Moore
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore » Sun Jul 28, 2019 9:16 am

Morpheus wrote:
Sun Jul 28, 2019 7:27 am
The cable I bought is a proper 128/+2 Cable
Then it’s not suited for the Peritel option. Use the +2A cable.
Morpheus wrote:
Sun Jul 28, 2019 7:27 am
I fitted a 470R Resistor to R9 (which was empty)
Ah. Are resistors R12–R14 and diodes D9–D11 present on the board?
The Peritel option requires the following jumper configuration:

Link 2
Link 1 (optional, depends on the pinout of the cable)
Link 8
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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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Re: Spectrum +2 Dark RGB

Post by 1024MAK » Sun Jul 28, 2019 10:23 am

I take it that you have found Paul’s site where he goes into detail about the various video circuits including that of the +2.

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Morpheus
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Re: Spectrum +2 Dark RGB

Post by Morpheus » Sun Jul 28, 2019 10:43 am

1024MAK wrote:
Sun Jul 28, 2019 10:23 am
I take it that you have found Paul’s site where he goes into detail about the various video circuits including that of the +2.

Mark
Yeah I have read that, It's what made me think about the wrong blanking signal. I checked the transistor and and I fitted a new one turned it around and got no picture at all fitting another new one got the picture back to a very dark/negative pickture with the link set back to L4.

I got no picture at all with the Modulator so I think the problem is more convoluted than just the monitor socket. So I will have a think on where I go from here.
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Re: Spectrum +2 Dark RGB

Post by Morpheus » Thu Aug 01, 2019 12:49 pm

I have been reading some of the other posts on here regards to +2's video and various things. I did some tests on the voltages and finding the 12V is only around 1.3V even on the edge connector. I'll do some more tests but that could explain why there is no modulator signal and/or it cannot switch into RGB mode when I was using the SCART either the original 128K/+2 Cable or the +2a cable.
So I have never had this problem before so looking for some help on fixing it.
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