Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Discussions about Sinclair ZX80 and ZX81 Hardware
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Flatulentia
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Flatulentia »

Yes. I'm not sure where would be tidiest, but pin 28 of the RAM IC goes straight to the +5V rail.
ZX81 with ZiLOG Z84 CMOS Z80, 32KB battery-backed Toshiba 55257 SRAM with charge status LED, Wilf's "Why Wait?" mod and switch-mode 5V regulator. 50/60Hz mode switch, composite video output with Zigg's back porch mod and 1080p60 HDMI output.
Lardo Boffin
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Lardo Boffin »

Flatulentia wrote: Sat Jun 03, 2023 3:12 pm Yes. I'm not sure where would be tidiest, but pin 28 of the RAM IC goes straight to the +5V rail.
Does pin 27 need isolating from the board before being connected to 5V?

Looking at the back it connects up to pin 23 (if I counted correctly) so I assume that will get 5V as well?

Edit - pin 23 is lifted so I guess it doesn’t matter.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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Flatulentia
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Location: Cambridgeshire, UK

Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Flatulentia »

Looking at the way mine's set up, you don't need to isolate pin 27.
ZX81 with ZiLOG Z84 CMOS Z80, 32KB battery-backed Toshiba 55257 SRAM with charge status LED, Wilf's "Why Wait?" mod and switch-mode 5V regulator. 50/60Hz mode switch, composite video output with Zigg's back porch mod and 1080p60 HDMI output.
mikeh_nz
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by mikeh_nz »

I’d suggest reading this post as well.
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Flatulentia
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Flatulentia »

mikeh_nz wrote: Sat Jun 03, 2023 6:02 pm I’d suggest reading this post as well.
That looks familiar! I remember reading that thread at the time as a visitor and thinking how lucky I'd been for everything to just work with no messing. :)
Last edited by Flatulentia on Sat Jun 03, 2023 7:27 pm, edited 1 time in total.
ZX81 with ZiLOG Z84 CMOS Z80, 32KB battery-backed Toshiba 55257 SRAM with charge status LED, Wilf's "Why Wait?" mod and switch-mode 5V regulator. 50/60Hz mode switch, composite video output with Zigg's back porch mod and 1080p60 HDMI output.
Lardo Boffin
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Lardo Boffin »

Thanks.

I have fitted a 10K between 5V and 27 but it made no difference. :cry:

IMG_2141.jpeg

Looks like I have some reading to do.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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Flatulentia
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Joined: Sun May 14, 2023 3:58 pm
Location: Cambridgeshire, UK

Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Flatulentia »

Me too by the looks of it. That schematic states that the 10K resistor relates to HRG8, but I have no idea what that means. As Mike suggests, you may be experiencing a completely different problem altogether.

Please keep us updated.

EDIT: This mod which is identical (as far as I can tell) to what you have now states...
It is also compatible with HighRes modes on the ZX81. It should be able to run WRX mode, but is also capable of running HRG8 mode, it has a 10K Ohm resistor between +5 volt (pin28) and Write Enable (pin27).
https://www.tindie.com/products/redhawk ... expansion/

...so it looks like it's most probably timing issues as were found in the thread Mike linked to.
ZX81 with ZiLOG Z84 CMOS Z80, 32KB battery-backed Toshiba 55257 SRAM with charge status LED, Wilf's "Why Wait?" mod and switch-mode 5V regulator. 50/60Hz mode switch, composite video output with Zigg's back porch mod and 1080p60 HDMI output.
Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Lardo Boffin »

mikeh_nz wrote: Sat Jun 03, 2023 6:02 pm I’d suggest reading this post as well.
Thanks Mike. Any idea where I would put the cap on an issue one board?
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Lardo Boffin »

Flatulentia wrote: Sat Jun 03, 2023 7:08 pm ...so it looks like it's most probably timing issues as were found in the thread Mike linked to.
Next step is to put a cap in there I guess. Anything more involved than that and it will be low res only!
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
User avatar
Flatulentia
Posts: 93
Joined: Sun May 14, 2023 3:58 pm
Location: Cambridgeshire, UK

Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by Flatulentia »

Mike put his across pins 8 and 9 of the empty IC4B space. That's going to remain the same regardless of ZX81 version as the RAM IC pin designations stay the same.

EDIT: It looks as though I'll be doing the same as mine runs plenty of other hi-res games properly but not the dr.beep ones I've tried so far today. :?
ZX81 with ZiLOG Z84 CMOS Z80, 32KB battery-backed Toshiba 55257 SRAM with charge status LED, Wilf's "Why Wait?" mod and switch-mode 5V regulator. 50/60Hz mode switch, composite video output with Zigg's back porch mod and 1080p60 HDMI output.
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