PAL 6561

[JonBrawn]

Wotcha!

Is the circuitry around the 6561 PAL VIC the same as that around the 6560 NTSC VIC, other than the crystal frequency?

And on a completely related note, why can't I find the schematics for a CR PAL VIC-20?!

Thanks for any help!

[MCes]

The reference schemes:
http://www.zimmers.net/anonftp/pub/cbm/ ... index.html

6561 have a little different clock input circuit,
only the pin 39 is sensible, pin 38 is internally NC,
I had a VIC 20 (PAL) with the non-soldered NC pin (folded under the socket at the factory ...) and it worked fine!
Into this forum somebody noticed this observing High resolution pics of a decapped chip...

The first batch of 6561 had a terrible problem: colour will change with duty cycle of clock that have to be exactly 50% (2% error is visible...),
and the chroma out is superimposed with levels derived from B / W levels (but not a direct relationship) ....
Probably this is the reason that a 4.43MHz clock (that can be directly generate by an xtal oscillator) is obtained by /2 division, operation that guaranteed the 50% of duty cycle. (also graphically on schematic the "/2 IC" appear as a modify).
http://www.zimmers.net/anonftp/pub/cbm/ ... 4001_1.gif

Someone worked on this also on NTSC VIC:
http://sleepingelephant.com/denial/wiki ... ifications

The next batch of PAL 6561 are not sensible to duty cycle error, in fact the CR board have 4.43MHz quartz without /2 IC (and them have better colours...)

[JonBrawn]

I have looked at Zimmers.net, where there are these files:

324001_1.gif1996-05-08177837 VC-20 rev.B (PAL, old design). Assy number 324001-03. Bad scanning quality.
324001_2.gif1996-05-08194380 VC-20 rev.B (PAL, old design). Assy number 324001-03. Bad scanning quality.
324001_3.gif1996-05-08170958 VC-20 rev.B (PAL, old design). Assy number 324001-03. Bad scanning quality.

However, the tag "old design" scarred me off - how "exciting" are the changes between this old design and the newer PAL systems, as far as the clock and video circuitry is concerned?

Thanks to the pointer to the article about improving VIC color quality - I'll definitely be having a play with that.