On Wednesday, August 29, 2007 at 10:20:28 PM UTC-4, James Littlejohn wrote:
> > I finally got my order from Jameco with the correct oscillator
> > frequencies this time. My results:
> >
> > 9 MHz is OK.
> > 10 MHz is not. Tried two different 40 MHz manufacturers.
> >
> To reach the 10Mhz and beyond range, you have to replace the two
> 6264's for some with faster access time. The original 6264's make the
> IIc+ crash just short of the 10Mhz mark. I installed 100ns chips in
> mine and am running a rock solid 10Mhz. I would like to get my hands
> on some 85ns ones and see how far I could push it.
> >
> > I can't wait for the flash disk/RAM/wireless card
> > to become available for the IIc++ now.
> You, me, and everyone else!

Hello, I'm posting in early 2023 so it's more than a 15 year gap here. Luckily Usenet permits necro-posting, and it isn't a SPOF private website that can just suddenly vanish, so I deeply appreciate this forum's ability to act as a resilient community memory bank - it is SO interesting to read discussions that started in the 1980's or 1990's, from the very start of the proto-internet, and in some cases have continued intermittently through the years up to now!

Case in point: on the topic of overclocking a IIc+, there was an important post on A2central.com by Sean Fahey, dated 10-Sep-2008. Unfortunately that site is offline since its owner Tony Diaz died in 2021, but I'd kept the URL of the post and so was able to retrieve it from the Wayback Machine: (http://web.archive.org/web/20211030203640/https://a2central.com/1586/overclocking-the-apple-iic-plus-just-got-easier/) and I want to reproduce it here for posterity. The preserved page includes a thumbnail image link to a large photo that shows, on the left side, a IIc+ motherboard with an NCR0380982 ASIC chip and a 40 MHz oscillator installed next to it, on the right side a UMC8944S ASIC chip with a 16 MHz oscillator by its side.

<begin copied text from 2008>
(Sean Fahey:) James Littlejohn has successfully overclocked his Apple IIc Plus to 10MHz with nothing more than an oscillator change and it works really well. Old news, right?
Overclocking the IIc Plus has been around awhile; hackers have been bumping the speed on the IIc Plus for years using various techniques. The most common procedure has been to replace the old oscillator, CPU and cache RAM with faster versions to achieve the desired speed increase (usually around 8MHz). You had to be handy with the soldering iron too.
Then earlier this year, we had a breakthrough; it was discovered that some IIc Plus boards overclocked with just an oscillator swap. It was still considered voodoo though, because while some boards readily overclocked, there were others that refused to go any faster than their native 4MHz. No one knew why… until now.
I visited James recently in Chelsea Oklahoma, and left a couple IIc Plus boards with him to upgrade. While trying to get them to work at 10MHz, he made some interesting observations that he’s allowed me to post here on A2Central.

(James Littlejohn:) While trying to overclock a couple of Sean Fahey’s Apple IIc Plus motherboards, I made a few interesting discoveries.
There are at least two versions of the Apple IIc Plus motherboard. You can identify them by the the silk screening which can be found under the power supply. The “A” motherboard is silk screened “1987/88”, and usually has socketed cache RAM. The “B” motherboard has “1987/88/89”, and features soldered cache RAM..
There are also two manufacturers for the ASIC chips used on these boards, NCR and UMC. The NCR chips appear primarily on the “A” boards (and occasionally on some “B” boards), while the UMC is found only on the “B” boards.
While experimenting with overclocking both boards, I’ve come to the following conclusions:
The “A” boards with the NCR ASIC are easily overclocked, as is. The “B” boards with the UMC ASIC will not overclock at all. However, some “B” boards shipped with the NCR ASIC.
Now here comes the kicker:
An “A” board with the UMC ASIC is able to be overclocked. So is a “B” board with an NCR ASIC. This suggests the NCR ASIC can be used in either version to achieve at least 10MHZ (maybe more — 40MHz crystals were the fastest I had on hand), without having to replace any stock chips. However, the UMC ASIC can only be accelerated in an “A” board.
I conducted these tests using 2 Apple IIc Plus “A” boards, and 4 “B” boards.
<end copied text from 2008>

For anyone else researching this topic, there is at least one video up on YouTube (channel 'NHB Retro'), and an old thread on AppleFritter.com (subject: '//c+ Overclock Project'), which also annoyingly contains cobweblinks to extra info, some of which may also be archived in the Wayback Machine.
James Littlejohn's description (from March 2007) of making a small board allowing him to switch between a 16MHz oscillator and a 32MHz (note, somewhere else James himself later admitted this was overkill because you can control the machine's speed using the Zipchip Utilities disk): http://web.archive.org/web/20081121021640/http://www.8bitsystem.com/computerIIc%2B/IIC%2Bstart.html
-Martin