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

Discussions about Sinclair ZX80 and ZX81 Hardware
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

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

Post by Lardo Boffin »

Hello all

I have done a 16K internal RAM mod using the quick method:

IMG_2086.jpeg

This works fine for pseudo hi res gams but not so much Dr Beeps excellent hires games.

Pinball does this:
IMG_2116.jpeg
IMG_2119.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
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 »

You can see the flippers and the ball bouncing around but there are a lot of issues!

I use one of these chips:

IMG_2121.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
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 »

I have seen kits for sale that say they have a resistor pre-soldered across two pins to support hires. Is this required?

Or are the chips not good / fast enough / the wrong sort?

Or is the track cutting method better?

:D
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 »

Page 1 of the spec sheet for the chip:
IMG_2122.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 »

Pure guesswork on my part, but maybe it needs the same resistor arrangement as the 32KB mod I'm running?

http://www.zx81.de/english/32k-rame.htm
if you want to run HRG8, connect pin 27 via a resistor of 10K ohms with 5 volts
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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Location: Boxmeer

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

Post by dr beep »

What about 16K true hires games?

I have 2
16K SHOGUN
and
USCII
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 12:09 pm Pure guesswork on my part, but maybe it needs the same resistor arrangement as the 32KB mod I'm running?

http://www.zx81.de/english/32k-rame.htm
if you want to run HRG8, connect pin 27 via a resistor of 10K ohms with 5 volts
Thanks. I have seen that mod but never done it. I sell all my refurbished zeddies and I’m not sure the lure of 32K would be worth the extra time to do. People are generally reluctant to pay much more for a refurbished / improved version than an untested one. Plus I’m no good at reading schematics. :oops:

Does the resistor just apply if using the full 32K? I’m only using the simple 16K version.
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 »

dr beep wrote: Sat Jun 03, 2023 12:28 pm What about 16K true hires games?

I have 2
16K SHOGUN
and
USCII
Thanks. I tried Dogcatcher and got this:

IMG_2124.jpeg
IMG_2126.jpeg

So I’m assuming there is something amiss with the RAM mod as far as hires goes.
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 »

Lardo Boffin wrote: Sat Jun 03, 2023 2:21 pmDoes the resistor just apply if using the full 32K? I’m only using the simple 16K version.
It applies to both as it's given as the last step of the 16KB mod instructions.
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
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 2:24 pm
Lardo Boffin wrote: Sat Jun 03, 2023 2:21 pmDoes the resistor just apply if using the full 32K? I’m only using the simple 16K version.
It applies to both as it's given as the last step of the 16KB mod instructions.
Thanks.

So pin 27 goes to 5V via a 10K Ohm resistor? Where is best to pick that up nearby on an issue one?
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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