Re: Apple II REV 1 repair

[Nama <forums6000@mac.com>]

On Oct 13, 1:55 pm, "Michael J. Mahon" <mjma...@aol.com> wrote:
> Nama wrote:
> > 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.
>
> Exactly--nice find!
>
> The intermittent short causing the "W4" issue may return.  Careful
> examination of the traces involved along their entire length--including
> the connector--will likely reveal the problem so you can make sure it
> is permanently fixed.
>
> > 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.
>
> I don't have a schematic handy, but you may find that there is a broken
> trace connecting the two points you have bridged with a jumper.  ;-)
>
> -michael
>
> Parallel computing for Apple II computers!
> Home page:http://members.aol.com/mjmahon
>
> "The wastebasket is our most important design
> tool--and it's seriously underused."
> ** Posted fromhttp://www.teranews.com**

Thanks again for all your replies. I narrowed down the cause of the
video problem to the potentiometer. I replace it and now the Apple II
is perfect. Thanks for all the input.

Philip