Hello,
I recently got an apple iic computer. It worked fine for about a week, then degarded with all sorts of random issues until it eventually stopped working. Just a screen full of random characters.
I figured it may be a RAM Issue so started to look for the circuit to help debug the issue. I can find iic cirtuits with the 16 chip ram setup but not one for the 4 chip ram setup.
Does anyone have it? or know where I can download it?
I got my iic working again, I tried the piggy back ram method to try and work out what was wrong. The only chip that made a difference was replaced. It did not work. So out with the scope, using the silk screen and the cirtuit for the normal iic I cheched the LS374 chips, video / RAM multiplex. Bingo bad logic (being dragged high) on pin 1. Rplace one of the two chips, improved to the point it would show text on the screen. The wrong text and very jumpy. I replaced the other ls374 chip and we have a working iic ! Yes winner.
I would like the circuit for this version. I'm sure it would have made it a bit easier.
Many thanks
Derek
I have never seen a IIc motherboard with just 4 RAM chips unless it was a IIc Plus. But I understand later versions did come that way.
If you're looking for the IIc+ schematic diagram, you can find it in the IIc Technical Reference, 2nd edition (emphasis on the 2nd edition).
If it's a regular IIc, I would still look in the same document. It was the latest version that Apple plublished for the IIc family.
The manual is here: https://archive.org/details/AppleIIcTechnicalReference2ndEd
Sadly that copy is unreadable on the circuit(s) pages. I'm looking for a better copy.
I've been looking for years - that's the best (probably the only) copy out there. It's duplicated on various sites and I'm told it was a scan from a hardcopy that used to be distributed by Syndicomm, Tony Diaz's former company and that the hardcopy was just as bad looking. This is all hearsay.
I once saw a hardcopy for sale on AbeBooks but it was like $250 (and there's a hardcopy for sale on Amazon for $266 but I think it's misrepresented as the 2nd ed and it actually the 1st ed) plus shipping (no thanks) and I'm told that the Syndicomm hardcopy is as bad as the version on the internet archive.
If you find one, post the link here.
Try this: https://archive.org/download/Apple_IIc_Technical_Reference_Manual/Apple_IIc_Technical_Reference_Manual.pdf
It has the 4-chip RAM version.