eprom replacemnt for zx81 rom

[jojo]

Can anyone help me out ,

lost a bit in old documents …………………

i have an ( untouched ) iss 3 zx81 with an 28 pin socket but without the rom , so my idea is to install an 2764 BUT how ??

[Paul]

There are countless 2364 to 2764 Adapter in the bay.

[jojo]

Thanks ,


I was thinking about the socket being 28 pins it could hold a 2764 directly by adding 3 extra wires ,

eprom 2 to eprom 22 , 14 wired to eprom 22 , eprom 27 to ....... ( the missing link ) .

going back a long time tough..........so i might be wrong there

[Paul]

flying wires are definitely possible, but its ugly and prone to defects.
https://www.sinclairzxworld.com/viewtopic.php?t=189
Thats why I recommend PCBs.
In fact I made a PCB myself that offers a plcc 27W512 with jumpers in a 24pin PCB as well as a programming adapter.
The 27W512 is an EEprom, so no need for UV light for erasing.
I'm going to test both PCBs this week and can offer some for sending to inner EC countries if they work as expected as I had 50 PCBs made instead of the wanted 5
Kind regards
Paul

[Moggy]

This is the diagram I use for all my 2764's plus one of my spare fast EPROMS..

Pin 2 should be lifted, also pins 1,27,28 should be lifted and joined so as to be tied to 5 volt. The easiest way to do this is connect those three pins to pin 26 which has no internal connection and whose position in the motherboard socket is conveniently at 5v. Pins 20 and 23 should also be lifted and their place taken by the link wires shown.

I find this very simple to do and as for being ugly well unless you have a see through case I don't see the problem with looks and as for being prone to failure sorry to say never had one fail on me yet.

If you do go the programming route remember these old devices are getting harder to find and those labelled 27C64 require a 12v programming voltage unlike the older 2764's 20 odd volts.

I would say at this point I'm rather old school and Pauls' method has considerable merit for those not equipped or inclined to dabble too much.

[1024MAK]

I'm going to test both PCBs this week and can offer some for sending to inner EC countries if they work as expected as I had 50 PCBs made instead of the wanted 5

So that may almost be one each for the active members of our community

I hope they work as expected

If they don’t work, and modification is not practical, I may have a use for defective bare PCBs.

Mark

[iturbez]

In fact I made a PCB myself that offers a plcc 27W512 with jumpers in a 24pin PCB as well as a programming adapter.
The 27W512 is an EEprom, so no need for UV light for erasing.
I'm going to test both PCBs this week and can offer some for sending to inner EC countries if they work as expected as I had 50 PCBs made instead of the wanted 5

Hi, Paul.
Have pcbs worked?
Are you going to sell any of those 50?
If so, I am interested in buying some.
Feel free to contact me if you are going to do it.
Regards.

[jojo]

@paul ,


any news ?? progress ??

[Paul]

Sorry, real life did take most of my time recently,
I'll really come back to this when I get time for this.
Kind regards
Paul