Re: strange c64 board

From: Nicolas Welte (
Date: 2000-02-07 21:45:50

An update on the strange board:

I checked the clock circuit, and the empty XT oscillator is just an
alternative source for the color clock. Yes, not for dot clock, it's for
color clock. The circuit is not worth drawing down, it is mostly a mix
between the older one from schematic #326106 and the newer one from
#251138. The output of XT is always connected to that side of FB16 that
is also connected to pin 10 of U31. But there is a jumper (half moons)
on the bottom side of the board that can be used to disconnect the
output of U31. That's all there can be done. I don't know if any boards
were ever manufactured that way, because the possibility to adjust the
color clock was not possible in this configuration. Probably U31 and the
components around it were not installed at all in that case.

Some other component locations are empty, they're C35, C37, C55, C58,
C73, C80, C87, R23. R22 is just a jumper wire. Except C37 these are
exactly the differences between the two documented boards, the new board
doesn't have these components locations at all. C37 actually is
installed in all large board C64 revisions I just checked, so maybe it
was just left out by mistake. The bottom side also has the PAL-G/I
jumper I already missed: it says "OPEN I.PAL  SHORT G.PAL" and it's
closed. There's also a board identification that says "FAB NO. 251022
REV.A". Unfortunately I don't have these numbers from the other boards.


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