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

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

Post by Lardo Boffin »

33pF improved it but 100pF has fixed it!

Edit - cap in board:

IMG_2364.jpeg

Many thanks to all!

IMG_2144.jpeg
IMG_2143.jpeg
Last edited by Lardo Boffin on Mon Jan 15, 2024 8:38 am, edited 1 time in total.
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)
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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 »

Yay! Thank YOU! I now know roughly what capacitor value I'm likely to need.
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.
dr beep
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Re: Internal 16K RAM mod doesn’t quite work with Dr Beep hires games

Post by dr beep »

Lardo Boffin wrote: Sat Jun 03, 2023 8:48 pm 33pF improved it but 100pF has fixed it!

Many thanks to all!


IMG_2144.jpeg

IMG_2143.jpeg
Just a question:
I see DOGCATCHER. How did you get that version?
The original is MAKE A SHIT and the version DOGCATCHER was intended to be used for a video only if the name MAKE A SHIT could be to offensive.
Did I release a wrong version?
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 »

dr beep wrote: Sat Jun 03, 2023 9:47 pm
Lardo Boffin wrote: Sat Jun 03, 2023 8:48 pm 33pF improved it but 100pF has fixed it!

Many thanks to all!


IMG_2144.jpeg

IMG_2143.jpeg
Just a question:
I see DOGCATCHER. How did you get that version?
The original is MAKE A SHIT and the version DOGCATCHER was intended to be used for a video only if the name MAKE A SHIT could be to offensive.
Did I release a wrong version?
From here:

viewtopic.php?t=3124
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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1024MAK
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Location: Looking forward to summer in Somerset, UK...

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

Post by 1024MAK »

In answer to the earlier question about the type of SRAM chip used, it’s because the modern chips have too quick an access time. The capacitor maintains the control signal for a faction longer. Hence the SRAM continues to output data for a bit longer, allowing it to be read. The hi-res timing appears to be more timing critical than the normal display routine.

The resistor in the other modification is only needed for configurations where you are trying to use battery backup.

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

Post by dr beep »

Lardo Boffin wrote: Sat Jun 03, 2023 9:54 pm
dr beep wrote: Sat Jun 03, 2023 9:47 pm
Lardo Boffin wrote: Sat Jun 03, 2023 8:48 pm 33pF improved it but 100pF has fixed it!

Many thanks to all!


IMG_2144.jpeg

IMG_2143.jpeg
Just a question:
I see DOGCATCHER. How did you get that version?
The original is MAKE A SHIT and the version DOGCATCHER was intended to be used for a video only if the name MAKE A SHIT could be to offensive.
Did I release a wrong version?
From here:

viewtopic.php?t=3124
Ah.... that's true.
It was a small demogame and it is not MAKE-A-SHIT from the 1K hires series.
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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 »

1024MAK wrote: Sat Jun 03, 2023 10:00 pmThe resistor in the other modification is only needed for configurations where you are trying to use battery backup.
I'll correct my saved copy of the schematic then as it says that resistor is for HRG8 and the other one is for battery backup. Thanks.
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 »

Lardo Boffin wrote: Sat Jun 03, 2023 8:48 pm33pF improved it but 100pF has fixed it!
I like your BBC owl coaster peeking out in the photo!
Lardo Boffin
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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 11:27 pm
Lardo Boffin wrote: Sat Jun 03, 2023 8:48 pm33pF improved it but 100pF has fixed it!
I like your BBC owl coaster peeking out in the photo!
The kids made it for me. You arrange loads of beads on a grid and then iron it to melt them together.

IMG_2153.jpeg
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 »

This is weird!

RudeDogRetros make the same mod I'm using (minus battery backup) as a plug-in module and that has a link that appears to either connect/disconnect that 10K resistor to enable/disable HRG8. This is the second commercial product I've found with the 10K resistor claiming it gives HRG8 capability.

Is everyone just copying it blindly and getting it wrong?

https://rudedogretros.co.uk/product/zx8 ... ade-board/
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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