Improvised 32K RAM?

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Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Improvised 32K RAM?

Post by Lardo Boffin »

I bought this for spares but was curious about the extra wiring and chip - a 32K RAM mod? None of the tracks underneath are cut.

32A20D9B-1218-47A5-BB97-D053A2C0BE6C.jpeg

A couple of the wires have come adrift and also R28 is broken so obviously I have not tried it yet!

697895AF-D3EB-4086-9D2D-3A7237E40948.png
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
McKlaud
Posts: 337
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: Improvised 32K RAM?

Post by McKlaud »

Well, well! Another "dead cockroach" mod :mrgreen:

Some time ago I did something similar but with SMD components. See below:
Image

Image
Claudius
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Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Improvised 32K RAM?

Post by Lardo Boffin »

Yours looks a little neater! :shock:
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
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Improvised 32K RAM?

Post by 1024MAK »

Could be one of two methods of RAM expansion, but the total amount of RAM looks like 16k bytes if it is two 8k byte SRAM chips connected piggy-back style. I’m on a train, and don’t have time to work out further details at the moment.

It looks like the solid core wires have broken due to stress fractures caused by the person doing the work using wire cutters to strip the insulation from the wire. The conductor has been nicked, and over time, movement causes this part of the wire to flex, then the stress eventually causes the wire to break at this point.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

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Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Improvised 32K RAM?

Post by Lardo Boffin »

You are right - it is piggy backed. I was so busy stealing the case and ULA :oops: (which seems to work ok) I didn’t notice.

019D4B11-89EA-416D-A370-742312E0ACC3.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
1024MAK
Posts: 5103
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Improvised 32K RAM?

Post by 1024MAK »

Err, from that view, it looks like they have piggybacked on top of the original SRAM chip! :shock:
So only 8k bytes of extra memory :(

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Improvised 32K RAM?

Post by Lardo Boffin »

1024MAK wrote: Tue Jan 14, 2020 7:39 pm Err, from that view, it looks like they have piggybacked on top of the original SRAM chip! :shock:
So only 8k bytes of extra memory :(

Mark
Its not the camera angle - it is definitely a smaller chip underneath!

A lot of effort for 8K. :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
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