ZX80 Oddity with Replacement ROM

[VectrexRoli]

I also don´t expect the modifications to have anything to do with my problem here. Both the old original CPU and the more modern one work fine with the old original 4k Sinclair ROM.
There is no corrosion on the ROM socket whatsoever, it is almost 0 Ohm on all contacts, depending on how hard I press down the probes of course, so everything looks like normal there and as I said the original Sinclair ROM also works.
Regarding ZX8 CCB: If I would have ruined the computer touching the ZX8 CCB nothing would work at all, but the machine works fine with the old ROM.
Unfortunately I don´t have any other test gear, I gave most of the stuff away many years ago due to space issues.

So for now I guess it is one of those 3 issues:

1) The content of the new replacement ROM is corrupt. I have no way for checking that and as I got also a replacement ROM already, how likely would it be I have the same issue twice?

2) Something in my setup "does not like" the Hi/Lo address/data signal levels in combination with the new replacement ROM.

3) There is some timing issue with the new replacement ROM, but I guess that´s not very likely, as that thing will be "super fast" compared to what was available back in the 80´s and it should only make issues when it would be too slow I guess.

[Moggy]

Quote.

"So for now I guess it is one of those 3 issues:

1) The content of the new replacement ROM is corrupt. I have no way for checking that and as I got also a replacement ROM already, how likely would it be I have the same issue twice?.."


If Charlie (and this is said with all due respect to my forum brother whose skills I have come to respect very much over the years) has somehow cocked up the programming of the chip then yes possibly corrupt content in both chips.


As you have countered every idea put forward I can only suggest you send the two chips back to Rich/Charlie and let them try THOSE chips in their own 80's rather than a chip of their own which may have been programmed long before yours and if the fault doesn't materialise then it would seem something further needs investigating with your own ZX80.

[PokeMon]

I am not sure about the CPU - is it original Zilog or a chinese copy like sold many cheap over eBay.
Any reason for choosing it with 20 MHz ?
Maybe can react fast on any spikes in unwanted manner which could also be a side effect on the replacement rom. By the way - anyone knows if this will give TTL levels (5V) or just 3.3V with 5V tolerance on inputs ?

[VectrexRoli]

One was an "original" CPU that came with the ZX80 the other one was just a CPU I bought a while ago for test purposes. In any case both work fine with the original ROM.

[sirmorris]

Late to the party as always Still, better late than never!

I'm with Moggy on this one. The most likely situation is that I have cocked something up - that is a _technical_ term, as used by us in the know

VectrexRoli - if you would be so kind then sending me the roms would allow me to investigate further. I will send the ROM from my own '80 which I know is working, and we can take things from there. Sorry you're having issues - though it's part and parcel of this hobby at times..!

C

[1024MAK]

it's part and parcel

Of course referring to the need to wrap up and sent it away...

Mark

[VectrexRoli]

Late to the party as always Still, better late than never!

I'm with Moggy on this one. The most likely situation is that I have cocked something up - that is a _technical_ term, as used by us in the know

VectrexRoli - if you would be so kind then sending me the roms would allow me to investigate further. I will send the ROM from my own '80 which I know is working, and we can take things from there. Sorry you're having issues - though it's part and parcel of this hobby at times..!

C

Will send the ROMs to you today, thanks a lot for your help!

[Moggy]

Late to the party as always Still, better late than never!

I'm with Moggy on this one. The most likely situation is that I have cocked something up - that is a _technical_ term, as used by us in the know

VectrexRoli - if you would be so kind then sending me the roms would allow me to investigate further. I will send the ROM from my own '80 which I know is working, and we can take things from there. Sorry you're having issues - though it's part and parcel of this hobby at times..!

C

Nice one Charlie.
The generosity in time spent, information and knowledge etc freely shared is something I love about this community.

I feel confident of a good outcome with this one VectrexRoli.

[VectrexRoli]

Got a new ROM today and this one is working great. Also my ZXpand works great on my ZX80, thanks Charlie!

[Moggy]

So a duff ROM then.