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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1024MAK
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Re: Spectrum +2 Dark RGB

Post by 1024MAK » Thu Aug 01, 2019 6:31 pm

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.

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Re: Spectrum +2 Dark RGB

Post by Morpheus » Thu Aug 01, 2019 7:19 pm

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 » Fri Aug 02, 2019 6:46 pm

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 » Sat Aug 03, 2019 4:36 pm

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 » Sat Aug 03, 2019 4:42 pm

Morpheus wrote:
Sat Aug 03, 2019 4:36 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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and zasm Z80 Assembler syntax highlighter.

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Re: Spectrum +2 Dark RGB

Post by Morpheus » Sun Aug 04, 2019 7:22 am

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 » Sun Aug 04, 2019 8:16 am

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

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Re: Spectrum +2 Dark RGB

Post by Ast A. Moore » Sun Aug 04, 2019 9:42 am

Morpheus wrote:
Sun Aug 04, 2019 7:22 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 7:22 am
need 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.
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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 » Sun Aug 04, 2019 12:12 pm

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 » Sun Aug 04, 2019 1:17 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.
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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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