Hello fellow retro enthusiast, I'm a VC collector from Australia.
A couple of months ago I acquired an NTSC Apple II Plus, and just recently I acquired an NTSC Applecolor IIe composite monitor. The Plus works great, I've installed a Microsoft Ram card and Softcard in it as well as a super serial II and disk II controller. Everything works great except for the color output.
I originally had some issues with the video output, the text was very faint and picture geometry was out of whack. But due to reading some posts on this forum, I managed to adjust the picture using the blue trim control on the motherboard. I now have very bright text and geometry is perfect, but still no color.
Things I've tried to troubleshoot the color:
1) I've tested that the monitor can display color using a DVD player and the monitor displays color fine.
2) I've adjusted all controls on the monitor and motherboard such as the color trim to no avail.
3) I replaced the crystal on the motherboard with a Fox 14.31818Mhz crystal, no change with the color.
The motherboard on the Plus is a pre-RFI, I think revision 0 board. Something curious that I noticed, it has a 2716 eprom installed at the front on the motherboard in the ROM SPCL slot with a label on it saying VIDEX LC Chip 1st Ed.?
Is there anything else I can do to get the color working, any help would be appreciated?
What program (in basic or disk) have you used to test the color?
Could you add a picture of the motherboard please? I would love to see if it's really a rev 0.
Forgot to mention that, I've tested Loderunner and Pacman both have color on AppleWin. I'm not sure it's a revision zero motherboard in fact on some further reading that I've done I don't think it is. I did a search on the Videx chip and worked out it's a lower case chip which says you need revision 7 motherboard, so I got that one wrong. I was going by the part number on the motherboard which is: 820-0001-0, going by this reference: http://www.apple1notes.com/old_apple/Huston_Stories_files/Board%20Revs%200%20to%204.htm, revision 1 was: 820-0001-1 etc., but it also says revision 0 didn't have a part number at all. I think the last digit after the zero of the part number on my board is just not stamped clearly there's something there but it's hard to make out.
my advice would be to first download the 2 most important books on this issues from asimov from
first pick up the :
Apple II Circuit description hires.pdf from winston D. Gaylor
you ought to pick the hires version because you surely want clear good scans from the circuitplans....
and second you should pick the Sams Apple II Trounleshooting and Repair Guide.pdf
both have excellent circuitplans of the different versions of motherboards....
both permit you to follow the trace of colorvideosignal and it´s related components
( and if your bord is from later version also from "colorkiller" signal )
If everything else is working and you know the monitor is good, then you are getting no or a bad color burst. If you have a logic probe or O'scope you can check for presence of the color burst easily. There are only a few gates in the color burst circuit, primarily a gate on each of the chips at B13 and B12 plus a few discrete parts. The RFI boards fixed the poor color killer circuit with an extra gate at A14, so you might want to check that chip, if you do have an RFI board.
If the color burst is present, but you only see monochrome on the monitor, it could be that the main system clock crystal has drifted in frequency over time and needs to be replaced.
I had this problem with one of my ]['s. It turned out the crystal was not quite right. It took me a couple tries to get a replacement that would output color, even though they were all labeled 14.31818. Most of them seemed to be either marked wrong, or too-far out of spec to trigger the color burst properly.
Either that or your color-killer is always activated...
The crystals that finally worked for me are:
They are also easily damaged with heat while soldering them in...
Thanks speedyG, I've downloaded both documents, I'll start going through them.
Could chips at B13 and B12 be defective and still output a monochrome picture?
I've got a bunch of spare chips, I'll try and see if I have replacements I can test swapping them out with.
With the other crystals that you tried, did you get at least a monochrome picture out of them?
I'm thinking this may be the issue with the replacement crystal I used. I thought ahead an I've only jumpered the crystal back in, so I can try different ones.
Yes, the computer worked, but no color was ever output. Just black and white...
if you read the cirsuit description, you will understand that the color signal is generated by shifting various parts of the signal slightly. So a drift of the main clocking generator or the delay in one of the related chips or gates within the path of the color signal may cause the loss of the color. You must also remember that there is a spread of tolerance within the chips from factory. If a gate is too slow causing too much delay this may be a problem. Besides in some later mainboards there is a switch for the colorkiller signal. That also can cause trouble. Then there is also a trimming capacitor, that is related to the colorsignal - it should be adjusted correct. So there is a bunch of issues you will have to check along the path of the color signal. And finally let´s not forget the standards... if you have a PAL version of the board using it on a NTSC Monitor, or vice versa, that also can cause problems. So patience will be demanded... it might take 1 or 2 days to trace back the real cause of the problem....