Apple helpfully marked the xtals with their own p/n, 197-0001. Does anyone happen to know what Pico-Farad rating is correct for buying replacements? 18pF?
Are there any other ratings that fall into a narrow range that I need to stay within? I'd like to order a reasonable supply, rather than one piece, to have on hand, and I'd rather not experiment with tolerances.
Looking at http://www.willegal.net/appleii/appleii-components.htm, the system is extremely selective in what will work properly.
Regarding your question about the Load Capacitance (CL) I believe this depends on the manufacturer/model you are planning to use.
IQD 14.318 MHz Crystal type LFXTAL034793Bulk specifies a Load Capacitance (CL) of 18pF
FOX 14.318 MHz crystal type FC4STCBMF14.31818 specifies a Load Capacitance (CL) of 20pF
Not sure if this answers your question...
Not really. First, the xtal for the ][ series must be a serial type, but the ][ is extremely picky about what xtal it will use. If you look at the notes on the URL that I posted, MW used several xtals and only one worked, which is now unobtanium. I am trying to find a suitable part, and knowing all of the specs for the desired part is critical, so that I can try to find some stock.
Apple did not mark or document the specs other than the frequency, which does not suffice to find a suitable working replacement, so it is all just a shot in the dark. I know that ReActive has them, but IDK if he will give me a bulk price. I plan to ask, so we'll see, but it would be nice to have a new source now that VISHAY/DALE XT9UNLANA14M31818 is not available.
The CL on the datasheet is 'user specified', as it is for a series, and p/n in question does not specify it. I have no clue what the values are outside of the Mouser info and the datasheet for the entire XT49U, as XT49UNL designates 'Series to be specified by customer'. Perhaps it is here that I am missing something, but again, there are a lot of issues using random serial xtals on the ][ series. I was hoping that something other than this part existed that would suffice.
Okay... I wasn't aware of the serial load problem.
The following link might help you here... I just came across when searching the iNet about a replacement type. They are talking about an ESR of 25Ohm... but read yourself.
Hope this helps.
I suppose I can try it if my present order part fails to work, but the lead time is fifteen weeks and the min quantity seems to be 1,000 units, which suffice to say, means four months at a minimum before I know if it works and 999 spare units to shovel off if it does not. :/
if it does work, hell, I might buy 1,000 of them just to have them. I need only sell 200 to break even. Hahahahahah. As if I can find 200 people that need one.
For reference, the part in question is:
The signal gen n the ][ is stupidly specific, being an artefact of 1977 off the shelf design, but by 1985, things were more universal. The issues involved are very specific. I ordered two xtals and I will see if they work. If not, I will contact Henry and order six or so so that I can have them. I would like to have 20+ in stock, but at the going price, that is less feasible. I also stocked up on all of the 74 series chips in the video circuit, while I was at it.
At the least, I did validate that the xtal is bad, as one leg completely disintegrated when I touched it (no heat, just a gentle lift). I had already repaired the other leg, but clearly the former owner did not take care of this board at all, at all. Heck, it has a 75LS174 where a 175 belonged, which I think is the cause of my component failures (short).
I was pondering why I had no clk, but a leg being faulty and ready to fall off made it quite clear.