Re: Hacking the Laser 128EX/2

[Rubywand <rubywand@swbell.net>]

Supertimer writes ...
> 
> Ok, so the Laser 128EX/2 (and the 128EX) operates at 3.6Mhz.
> But why stop there?  There has got to be a way to boost the
> speed above 3.6Mhz.  Now before anyone says ZipChip, it does
> not work with the EX/2 (or, I suspect, the EX).
> 
> However, I looked around the motherboard and found two
> crystals.  At location XTAL1 is a 14Mhz crystal.  At location
> XTAL3 is a 3.6Mhz crystal.  Does anyone know if the crystal
> at location XTAL3 controls the CPU?  I'd like to boost the
> speed of the 128EX/2.
> 
> By the way, all the RAM chips are socketted, so I could put
> in faster ones too.  Currently, they are 120ns chips (faster
> than the ones in the IIe, for example).


     The "14MHz" may be 14.318MHz, as in the Apple II. It can be divided down
to get the color burst signal (3.5795MHz) and assorted Apple II frequencies.

     So, if the Laser really runs at 3.6MHz, the 3.6MHz crystal is likely to be
the one setting the uP clock frequency. What's kind of odd is that Laser
wouldn't just use the color burst frequency-- 3.5795MHz is not a whole lot
slower than 3.6MHz.


     Which leads to an alternative explanation for the two crystals. That is,
"3.6MHz" is really 3.5795MHz and this is the uP clock _and_ color burst. The
"14MHz" osc could be used to supply Apple II compatible signals. Using two
oscillators could eliminate some countdown chain IC's and reduce cost.

     If the "3.6MHz" osc supplies both color burst and the uP clock, changing
it to, say, 4MHz could mess up your color. A possible way around this would be
to locate the line going to the up (and any other non-video stuff), cut it, and
use a new osc.



Rubywand