Re: Apple II REV 1 repair

[Nama <forums6000@mac.com>]

On Oct 12, 2:37 pm, Nama <forums6...@mac.com> wrote:
> On Oct 12, 4:56 am, m...@willegal.net wrote:
>
>
>
> > 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
>
> Thanks for the replies. I have gotten the apple II up and
> running...almost. The sometimes boots from floopy, and sometimes
> doesn't was a RAM issue. Ram replaced.
> I still not sure exactly what the issue is with the video, but it's
> working after I jumpered between 2n3409 @ 14J to the single video pin.
> Crystal clear image. so I'll need to look into that further. Thanks
> for your suggestions on this.
>
> The only big remaining issue is the early rev 1 keyboard (without the
> encoder). I have fixed a couple of these before, but this one has me
> stumped. I have already replaced the 5 keyswitch which was smashed,
> and now it works well. The keys that don't work are 1, 2, R, and F. K
> is also a little intermittent, but thats an easy fix. and finally
> pushing either the 4 key or the W key both display  'W4'...maybe there
> is a short somewhere between these keys.
>
> Shorting the contacts on the rear of the board, on keys 1 or F makes a
> 1 or F appear on the screen, so I can assume the problem is just a
> keyswitch issue. However shorting the contacts on R and 2 do nothing!
> Maybe a dead component elsewhere is causing this.
>
> If anyone has any insights again, I would greatly appreciate your
> help.
>
> Philip

Ok...replying to myself here.
The 'W4' issue solved itself with a couple of little twist of the
keyboard circuit board.t. The other keys were fixed by either
reflowing the solder to the joints, or by replacing the keyswitches
altogether. I should let you all know that when I got the Apple II,
the keyboard was visably bowed The keys in the middle of the keyboard
were about 5mm lower than those on the ends. Someone had been pounding
on those keys over the years and had bent the metal rails that keep
the circuit board straight. With some force I straighten the railings
(which are riveted to the board) and maybe during this process some of
the solder connections to the keyswitches may have broken loose, could
this be why a couple of the keys could be fixed by reflowing the
solder.

So all fixed apart from the video issue. I don't really want to keep
that jumper on forever, so, I'll be looking at that part again soon.
But for the time being I'm very happy. From completely dead with
smashed and missing keyswitches, to fully functional in less than 2
days. The serial number for this machine is #12097, so if feels good
to bring another early one back to life.

Thanks again
Philip