2 Sep
2011
2 Sep
'11
1:27 p.m.
You could, for example, order a CMOS Si510 programmed
to the frequency
you're after. SiLabs apparently do free samples of some of the
fixed-frequency chips...
Hmm.. I feel that the aim of a computer restoration (as here) is to keep
the design as origianl as possible, and not to use devices that clearly
were not available (or anything like them) when the machine was made.
I would not want to replace th clock oscilaltor in an Apple ][ with one
of these chips, therefore. Particualrly since a crystal that 'will work'
is avaialbe.
Alternatively, if you can find a cheap crystal for a
frequency a bit
higher than the one you want, you could try "penning" it down:
http://www.hanssummers.com/penning.html
I believe you can also increase the frequency by careful griding or
etching/ The etchants are darn nasty (HF is one of them...) and I suspect
it's tricky to do anyway on a sealed-can crystal. Some of the older (50
year old) crystals were in screwed-together cases and could be taken
apart for hacks like this.
But as I said in a nearlier message, since the OP doesn't have a US model
(IIRC), but has several Europlusses, I'd be inclined to revers the
Eurapple mod and fit the 14.31818 MHz crystal (which you can get),
converting to to the US model.
-tony