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differences between ZX spectrum issue 2 and issue 3 boards

VERAULT

VERAULT

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Location
Connecticut, USA
I have another ZX spectrum issue 2 board which I am convinced has some intermittant breaks in traces. Its proving a real frustration to fix. I have found no the gerbers for the issue 2 board online but issue 3 boards are out there. Has anyone come across issue 2 board gerbers? If I was to swap all the components from my issue 2 board to the issue 3 what additional components do I need to source? Is it feasible? If so does anyone have an issue 3 board to sell me? I am guessing I would need the heatsink from an issue 3 as well?

thanks

Mick
 
Off the top of my head I think all the chips are the same. There may be some slightly different passives (and the iss3 certainly does away with the variable capacitors to adjust colour output). You could just replace the 7805 with a modern switching regulator and wouldn't need a heatsink at all. It seems a bit awkward to swap everything and would probably be a headache, especially as both iss2 and 3 spectrum boards are pretty easy to find. I think I'd probably try to find another working iss2, remove the chips from the broken one to test in the good one and then keep them as spares.

Someone re-made the iss3 board, that's why there are gerbers for it. As it's technically better than the iss2 no one has bothered to reverse engineer the iss2 (I assume).
 
Chr$ said:
Off the top of my head I think all the chips are the same. There may be some slightly different passives (and the iss3 certainly does away with the variable capacitors to adjust colour output). You could just replace the 7805 with a modern switching regulator and wouldn't need a heatsink at all. It seems a bit awkward to swap everything and would probably be a headache, especially as both iss2 and 3 spectrum boards are pretty easy to find. I think I'd probably try to find another working iss2, remove the chips from the broken one to test in the good one and then keep them as spares.

Someone re-made the iss3 board, that's why there are gerbers for it. As it's technically better than the iss2 no one has bothered to reverse engineer the iss2 (I assume).
Click to expand...
Thank you for the information. But you are forgetting I am in the States and ZX spectrums of any type are incredibly rare here. They just cannot be found without buying from Europe.
 
Yes, fair enough. I suppose the postage cost is a factor there (and import tax etc). I think it still probably work out a lot easier than swapping everything onto a new PCB as you'd have to check all the values of the passives and make sure everything else is correct, which would probably involve further research, you may have to source other components and potentially may need answers to questions that have never been asked before and with no guarantee of it all working out in the end.

What is the nature of the fault with the board?

You know what, I've got a spare Iss2 board and I think it works. I bought it because it's a very early one and has the dead cockroach mod on/around the ULA chip, which I wanted to remove in order to restore an Iss1 board back to its original state - so it would be minus the ULA and cockroach. Just checked it and it's in very good condition, even has virgin expansion port (PCB solder unscratched).
 
Main differences are the ULA they commonly come with. Some ULAs require additional mods but later ULAs will work with all revisions.
Otherwise, the chips are all pretty much the same. Heatsinks are the biggest difference and the color video section changes also.

You can build am Issue 3 with all new chips, and just move the ULA across - that works OK. And at least you can always put it back to the Issue 2 board.

Schematics vary slightly but are mostly the same.
Getting a PCB from the UK might still be easier, even with the shipping charges. Also you can get replacement ULAs for all models, so building an Issue 3 from scratch is quite possible.

And IIRC, you're pretty experienced at fixing them now.

As for track issues, I'd suggest just getting a diagnostic rom and trying to get the fault to occur while it's plugged in. It will give you a much better idea where the faults may be.

David
 
Seems An issue 3 boarrd would be a gokd route unless someone has an issue 2 board they can sell for a fair price to the states.
 
Oh were you offering the issue 3? I mean if its just a drop in replacement sure. Does it work? What chips does it need I can take from my issue 2?
 
It has a failed ULA so it got used as a source of spares, I think its RAM chips I removed, but of course without the ULA its not going to work :(
 
I can use the ULA off of mine if the rest of the board is ok ( I understand it needs RAM) My ULA runs very hot but it works.
 
there are no guarantees but if you PM your address I'll see what it costs to pop it in the post. Cant imagine its much.

btw, i was assuming its the ULA but it could be anything of course, I didnt do any real investigation, but you might as well have it.
 
Im in no rush on this. Plenty of other projects etc. If you want to wait until after the holidays more than fine by me. Ill send the PM.
 
@cj7hawk Yes but not with my original board. I threw in the towel when someone offered me a good working board. This was for my wife so after a couple years had gone by and I made little progress I was loosing steam. All the Ics on that board including ram are good but it gives such intermittant results. Im pretty sure its got a broken trace or two.. maybe to a via. I figured now that She has a fully working machine Might as well sell the parts.. As looking at them brings bad memories.

Its tough to work on a sinclair here in the states when there are virtually no spares I can use in the country And everything needs to be bought from overseas. My plan was to repair this bosrd snd buy a brand new chassis and keyboard for it... but I have so many projects and i want to get more into my 8 inch machines this year especially my Cromemco. I wish I had access to more speccys. I shoukd just buy a couple on the cheap online and have them shipped to my Sister in Law in the UK to hold onto until our next visit. Maybe finally find a Beeb.
 
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