Sinclair ZX80 / ZX81 / Z88 Forums

Hi all

Has anyone done this mod on the issue one zeddy?

http://blog.tynemouthsoftware.co.uk/201 ... n.html?m=1

It looks slightly less invasive than the full blown cut the tracks option and was interested in giving it a go.

Are the address lines in the same place on an issue one?

Many thanks

Lardo

On the RAM chip, yes. I can’t remember if the layout of diodes is exactly the same, but it’s not hard to work out.

Bending pins of chips out was popular in the past. Just be careful with regards to static, ensure you use an iron that has an earthed bit (unless it’s a gas or battery iron).

This method does have one disadvantage. It’s not easy to swap chips around when fault finding.

Mark

Thanks Mark. Good points.

Yeap,

To be honest you need 3 wires only. A10 line is connected via L2 (link) to the new memory chip.



And don't forget about 10k resistor between pins 27 & 28.

McKlaud wrote: ↑Thu Dec 06, 2018 11:33 pm And don't forget about 10k resistor between pins 27 & 28.

.. which is not necessary for this use case

Maybe it has been necessary for ram extensions, which had a battery (to write-protect the ram during power-off state) ...

Siggi

Now to find a source of HM62256ALP chips that wont take a month to arrive..

The currently available modern DIL 32K byte SRAM chips should work
E.g. this type LY62256PL-55LLI available from Farnell.

Not that I have actually tried this make/type yet.

Mark

I ordered some HM62256ALP-10s this AM with 28 pin dual-swipe sockets. If there is interest, I will sell them in the states as I ordered a few. Now I get to wait.. And wait... And wait...

Wellp.. My "RAM" arrived from China today. WRONG chips. I am not the proud owner of 10 "ATMEGA328P" chips.. wheeeeeee No 16K for my T/S 1000s.. No sir.

lame

Sorry if this is a Captain Obvious question, but I want to make sure I'm absolutely correct before starting - Link L2 also needs to be joined as well?