After a week of cleaning keys, reseating chips and all that, I finally have a fully working Rev 02! Except one thing -- when I first power the computer on, the video is vertically in the wrong position.. like the whole thing is moved down two lines or so, so the Apple ][ logo is lower than it should be, and you can't see anything when you get to the bottom lines as you type. If I tap my composite connector at the back, after a few taps, sometimes it reverts to the correct position. But it doesn't always hold.. you can see it starting to wig out a bit, and then finally move down.
Any thoughts on this? My cable is def. good. Wondering if the II is just not getting along with this monitor.
Hello falter,
there are seveal possible reasons for this behaviour:
1st: the monitor does not catch properly the VSYNC signal
a) try to adjust that at the Monitor ( at the VSYNC trimmer )
b) alternate: enlarge the videosignal by the videotrimmer at the mainboard
( Video Level R11 200 Ohm at position J to K 14 )
maybe adjusting both to get best result ......
c) the Q3 transistor 2N3904 at J14 besides the Video level trimmer is a general purpose transistor
with a wide range of amplification ..... some of that trasistors have a really poor amplification and a
replacement by another one with better amplification might solve the problem or the resistor R8 ( 2 kOhm)
that "injects" the V-signal in the transistor is not within the specs ( too high resistance ) and replacement
of that resistor might solve the problem.....
2nd: wrong timing generated at mainboard:
the main vertical sync signal is generated by the 74LS08 ( at B11 ) the 74LS04 ( at C11 ) and the 74LS51
( at C13 ) and small part by the 74LS32 at C14 ).... maybe one of the chips is bit out of specification
by aging heat or oxydation of contacts ..... try out if swapping one of that 4 chips with known good mainboard
uncovers bad behaviour of one of that chips....
sincerely speedyG
Thanks Speedy.
I'm thinking I might try a reseat on those three chips. I was having intermittent memory problems with this machine before and found reseating the RAM chips made problems go away.
Would either of the two things you suggested explain why if I tap the composite cord where it goes into the computer it sometimes bounces to the correct place and stays there?
I suppose just to rule it out, you could try a different composite cord, and maybe look at resoldering the composite connection. My //e composite connection can be fiddly sometimes, if I bump it the output on the monitor gets a little blurry, hard to describe. I can usually tap it back into looking good.
Also try a different monitor, again just to rule it out.
Maybe...
http://www.applefritter.com/content/fix-a2m6021-monitor-rear-rca-jack
Thanks guys. Speedy's suggestion on ICs proved to be the right thing. I did clean up the composite connector (the cable is new and works fine with other devices), but all that did was eliminate my ability to tap it and get the picture aligned correctly. For the third time, it turned out to be an IC that just needed reseating. I pulled the 74LS04, put another in.. bam. Video fixed. Then I re-installed the original.. still fixed through seven off and on cycles, multiple removals of the cable.
So that's it. A fully working, almost entirely original Rev 02!
One question though. The colour on a Rev 02.. is it supposed to be different than a IIe? I'm trying my Tracer Sanction game, and it looks like this:
http://i1381.photobucket.com/albums/ah216/unclefalter/20151126_213246_zpspikmv6kd.jpg~original
It's very.. purple-y. I'm not sure how to tell if I've got it right.. Apple II color is a bit weird to me.
Hello falter,
you should bear in mind how the videosignal is "assembled" together by
shifting portions of basic color signals and adding them together up
to one signal and also bear in mind that at the II series that signal
was a poor "replication" of the "NTSC Standard" a bit shifted besides.....
( reminding to reread the related chapters at Winston Gaylor or Jim Sather....)
so the colors are defined / determined by slight shiftings / delays in the video signal....
so minor delays in the signal path may cause major effects in the output
of the colors.... ( i mention this respectively adressing to the "delays" caused by logic gates in the chips )
and also remember the way the so called "color killer" circuit was designed at the II series
thats the reason for the color trim capacitor....
that changed at the IIe when the timing was collected together in 2 basic chips.....
sincerely speedyG