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 »

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 »

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.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

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and zasm Z80 Assembler syntax highlighter.
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1024MAK
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Re: Spectrum +2 Dark RGB

Post by 1024MAK »

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 »

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 »

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 ;-)

Mark
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

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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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

Morpheus wrote: Sun Jul 28, 2019 8:27 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 8:27 amI 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
Every man should plant a tree, build a house, and write a ZX Spectrum game.

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and zasm Z80 Assembler syntax highlighter.
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Re: Spectrum +2 Dark RGB

Post by 1024MAK »

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
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

1024MAK wrote: Sun Jul 28, 2019 11:23 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 »

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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Re: Spectrum +2 Dark RGB

Post by 1024MAK »

That’s the same problem as experienced by plenty of 16k/48k/plus machine owners. One, or both of the transistors used in the DC/DC converter circuit have been killed. Or less likely, “the coil” has failed.

In a +2 grey, the relevant transistors are: TR8 (ZTX213) and TR9 (ZTX650). TR9 is almost certainly dead, TR8 may or may not be faulty.

Replace TR9 with a ZTX651 or a ZTX653. Replace TR8 with a ZTX750 (matching lead-out) or a good quality NPN small signal transistor (may have a different lead-out).

After removing TR9 test for shorts on the +12V and on the -12V supply rails before soldering in a new transistor.

Mark
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Thanks I have just ordered some from Phil Ruston so should have them by the end of the week hopefully or Monday and then I can have a go and try and fix it.
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Hi,
Just as an addendum to this I found that D18? or the 5V1 whichever that one is was broken and I mean physically cracked into two halves. I haven't got the 12V back online yet, still awaiting replacement TR9 and TR8. If that fails I have a working spare coil I can try.
So once they are in and I have tested it I'll update this thread.
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Replaced TR8 and TR9 today, now have 12V on the Edge connector and on pin 11 of the TEAC. Cannot get it tuned in on the modulator but the RGB socket works. Just need to sort the noise on the audio that +2 Greys were prone to.
In all other aspects it runs fine so have saved it from the scrapyard :D
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

Morpheus wrote: Sat Aug 03, 2019 5:36 pm Just need to sort the noise on the audio that +2 Greys were prone to.
From my thread on WoS:

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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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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Yep already done! :D

Noise is hum from the Cassette unit - disconnect it and the noise/hum vanishes. I probably won't use it much but need to fit an external Ear socket so might have to live with it. I do have external AY interfaces to get stereo AY minus the Beeper if I really want to listen to the music/fx. I am contemplating replacing the PAL with a GAL 16V8 but I would need to clip the PAL out as I wouldn't be able to desolder it without damaging the PCB given my experience with other parts on the PCB it's very flaky.
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Re: Spectrum +2 Dark RGB

Post by 1024MAK »

See this thread (Correction of +2 hardware errors) over on World of Spectrum ;-)

Mark
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

Morpheus wrote: Sun Aug 04, 2019 8:22 am I am contemplating replacing the PAL with a GAL 16V8
I’d advise against that. This is a mod that will alter the behavior of the +2. We already have plenty of emulators that have that same “mod.” You’ll also lose the “precious” ULA snow effect. I’d leave it be. ;)
Morpheus wrote: Sun Aug 04, 2019 8:22 amneed to fit an external Ear socket
Be aware that you’ll also need to replicate the original 128K circuitry that cuts of negative swings of the audio signal fed into the ULA’s EAR pin. While it might be okay as is, it is rumored that the ULA might be damaged if the signal goes below 0V. You basically need a diode to take care of that. A capacitor in series will also remove the DC offset. Check the relevant part of the 128K schematic for more info.
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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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Thanks, I’ll leave the PAL as is based on your advice. I wasn’t keen on clipping it out as it was a one-way choice. I was looking at the mod that connects the ear input of a new mono socket to pin 5 to the LA6324. Then I can use my TZXDuino I was also going to try extra grounding on the cassette unit where the hum originates from.
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

If you add the extra circuitry, you could replace the 3.5 mm jack with a single TRS one and wire it the same way it’s wired on the +3. If you don’t want to bother with all that, you can just buy a generic cassette adaptor. They’re cheap and work well.
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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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Ast A. Moore wrote: Sun Aug 04, 2019 2:17 pm If you add the extra circuitry, you could replace the 3.5 mm jack with a single TRS one and wire it the same way it’s wired on the +3. If you don’t want to bother with all that, you can just buy a generic cassette adaptor. They’re cheap and work well.
If I remember you made a video of this using something called a Schmitt trigger?
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

Morpheus wrote: Mon Aug 05, 2019 4:52 am If I remember you made a video of this using something called a Schmitt trigger?
Nope. Definitely wasn’t me. Perhaps you’re referring to this video from Joules per Coulomb:

https://youtu.be/qUIv-A_DOc0?t=1014
Every man should plant a tree, build a house, and write a ZX Spectrum game.

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and zasm Z80 Assembler syntax highlighter.
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Re: Spectrum +2 Dark RGB

Post by Morpheus »

Yes, sorry I think you posted it a while back and I thought you had made it. My bad :oops:
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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore »

Morpheus wrote: Tue Aug 06, 2019 9:33 am Yes, sorry I think you posted it a while back and I thought you had made it. My bad :oops:
No worries. I’m actually flattered. :D
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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Re: Spectrum +2 Dark RGB

Post by Treguard »

Sorry for reviving an old thread, but I have this exact same problem with a +3. Very dark, grey output from the RGB port.

Looking at the motherboard I can’t find TR8 or TR9 at all, so I’m assuming the +3 is different or I’m being stupid in some way!

Anyone got any suggestions for a +3?

Not sure if it related but the output from the RF unit is completely black. The RGB scart compatibility modification has been done by the previous owner.

Thank you.

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