Re: Apple II REV 1 repair

[mike@willegal.net]

According to my 1982 RCA SK series replacement guide a C1214
transistor has
an RCA replacement of a Sk3124/289 which is an NPN transistor with
similar specs to
2n3904.  If it is wired in correctly, I would think that it would
work.  It is only connected
to the color burst signal, so worst case is that the color wouldn't
work.

Check voltages on  the inputs the each of the three resistors going to
the video circuit, as well
as the output.  It is easier and faster to debug these problems with
an oscilloscope or logic probe than
by working blindly.

Regards,
Mike Willegal

On Oct 11, 12:15 pm, Nama <forums6...@mac.com> wrote:
> Hi,
> I'm trying to bring a very early (serial # in the 12000's) rev 1 Apple
> II back to life. I have been using the swap method to interchange
> chips from a known working apple II+ motherboard.
> At first it was completely dead, and so far I have now gotten it to
> beep, power light comes on, and about 50% of the time it will access
> the disk drive and look for a floppy, but no video at all!
> If I insert DOS 3.3 disk on the times it is looking for a disk, It
> will seem to boot, and I can then do a blind IN#6 and the drive will
> boot again, so I'm assuming at least some of the time the machine is
> actually functioning at a basic level, However when the drive works,
> or does not work seems totally random, and is probably a separate
> issue.
> I think my first and biggest hurdle is to get the video working. I
> have replace all the IC's in the video circuit (and many more) without
> change. There is nothing on the screen at all, and It is completely
> blank. I'm don't even think there is an onscreen flicker when I turn
> the machine on and off.
>
> With further inspection of the video area I noticed that someone has
> done a bad repair of replacing the 2n3904 npn with a c1214(?). At this
> point this seems like the likely culprit, but before I try to fix the
> dodgy repair (some pad damage) I wanted to see if anyone else would
> agree that this could be the suspect video part.
>
> As usual, thanks in advance
>
> Philip