EEVblog #788 - Apple IIC Teardown

[TheNewLab]

and 128K was a lot of memory back then...In fact. just to get 20Mb it required a machine about the size of 3 brief cases. 120v AC and a fan the size of an auto radiator fan running constantly.

[Godzil]

The earliest macintosh I still have, which is a Macintosh SE, still have it's 20MB hard drive, and it still work ! (nearly the same as dave did a teardown, mine have a 1.4MB capable floppy drive, it's one of the latests version of the SE)

And I still have a backup of that drive in 9 floppy if I remember correctly...

[Godzil]

Hi Dave, I would like to request your help with your own Apple IIc.

I've got one last weekend, but the video output is not working, or should I say, the video signal is not what a composite screen would expect. There is an existing cable from the video, called Chat Mauve that transform the non standard "video out" signals to scart RGB, I didn't tested mine, but it seems that it also does not work.

Apart from the missing video, the IIc seems to work as it try to read a floppy, react to Ctrl+Reset, and basic seems to works as I manage to make it doing funny beeps.

What I've already done is to check the +5V rail, it's wobling a bit between 4.8 and 5.2V (it seems to be a 50Hz wobble, need to check that) it's far from perfect, but as the rest of the device work I would says that it's OK, but still need to check the caps in the DC2DC converter.

The other things I've checked are the signal comming to and from the SIL chip dubbed "VID" referenced as UE1 and was going to check the signals that goes out of the "digital" video output connector:



I will attach, or put in another post the screen captures from my scope of all of this signals

I would like to know Dave if you could do a capture of all of this signal from you own IIc as I don't have any reference here for these signals
And if anyone on this forum that knows how the video generation works in a IIc could help me to check what is wrong, I would be really grateful.

I'm absolutely not an expert in video signals and don't really understand what the UE1 thing is there for.
I suspect it's something about mixing the SEROUT signal (comming from the CHAR GEN) to pin 1, the SYNC signal (pin 2), CREF (color Ref, pin3) and CLRGAT, but how? I have no ideas.


Edit: interesting, SEROUT is now completely flat, I'm sure it wasn't yesterday, and CHARGEN is clearly outputting something, so the culprit could be the 74166 (marked as a LS on the schematic, but is really a HCT, go figure)