What chip is that? The mod is a single chip and four bodge wires
What PCB is that? Red on the back and yellow on the front. Looks like a ZX81 PCB Issue 3
I paused the video and the chip has marked on it "CY62256" which is well-known on here. And it is static RAM. The kind that was prohibitively expensive back in the day, but is now only $4 in USA
he did seem to zoom right along with the soldering ... how long was the video
The 32K chip is CY62256NLL but i'd guess that any type 622256 with 28-pin package will work?
he used a "quite nifty Japanese engineering solder sucker" to remove the existing 1K chips (2 smaller chips). I can read the name in the video still ENGINEER SS-02 Solder Sucker. Followed up with using desoldering wick on some of the pins
Vorticon wrote: ↑Sun May 22, 2022 2:49 pm
Thank you!
One question: will this modification affect the functionality of the ZXPand?
The ZXpand will occupy from 8k - 48k, so cannot work with this.
The only place left for memory expansion with the ZXpand, is between 48k - 64k. The only memory expansion I know of, that can be configured to only add memory to 48k - 64k, is Chroma 81 interface.
I did the track cutting version internal 16K RAM mod on an issue one on Sunday and it took 45 minutes.
Of that around 20 minutes was safely (from the motherboard’s perspective) removing the original RAM chip. Clearly I need to practice!
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
I didn't dig into detail but the question if ZXPand works with this woke me up.
ANY RAM (specially internal) should obey the /RAMCS signal.
This means any part that drives the CS of a RAM chip should do this via a resistor and be connected to the external BUS so it can be overridden by 5V connected to this pin.
This way internal RAM expansions work with external devices.
Notice: using the existing /RAMCS of the ZX81 only gives 16K of RAM that can be disabled from external devices such as ZXPand.
I know my English is terrible so please correct my post to remove unclear parts.
Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.