There are 2 Rev’s of motherboards. The silk screen can be found under the Power supply. One has silk screened “1987/88″, this is the Rev A board, with socket cache Ram. The other one is silk screened “1987/88/89″, this is the Rev B board, with soldered cache Ram.
There are also 2 manufactures of the ASIC chips used on these boards. The ASIC with the marking of “NCR” were primarily used in the Rev A boards. The ASIC with the marking of “UMC” were used in the Rev B boards.
The Rev A boards with the NCR ASIC are able to be accelerated as it.
The Rev B boards with the UMC ASIC are not acceleratable.
Some Rev B boards came with the NRC ASIC.
Now here comes the kicker:
A Rev A board with the UMC ASIC is able to be accelerated.
A Rev B board with the NCR ASIC is able to be accelerated.
So, the NRC ASIC can be used in both Rev of motherboards to achieve at least 10MHZ, and maybe more,* without having to replace any stock chips.
The UMC ASIC can only be accelerated in a Rev A motherboard.
* – 40Mhz crystals are the largest I had on me when this test was done.
This test was done with 2 Rev A boards, and 4 Rev B boards.
Having a little time today, I spent it on researching the IIc+ problem. Why would some boards allow you to change out the oscillator to speed them up, and others would not. Well I am happy to say now, I know why. I’ve got my best people on it. (OK, only one person, but it sounds better the other way.) Soon we may have a solution to this problem. Details are to come….
Saturday morning finally arrived, with the light rain outside, and the warming up of solder stations inside, I awaited the arrival of Sean Fahey from Kansas. The work benches had been cleared, almost all parts had been located for the scheduled day of hacking on our favorite computers, the Apple II’s.
Sean brought a couple of IIc+ motherboards for me to bump up to 8-10Mhz, If I could only of found the parts I knew I had, but alas, they were hiding from me real good. ( I never found them, but ordered new.)
Then we moved on to the next project. Installing a LittleExpanderPlus in his favorite (workhorse) Apple IIe. This was the project that inspired by Sean’s idea to put the Switch-a-Slot (that I had been working on), and the LittlePower together in one unit, to utilize the “free” space that was acquired by removing the internal power supply. Hence his name, immortalized forever, on every LEP that I make.
Just like Kfest, before we knew it, the day was over. Sean had a 3 hour drive back home with his new “Geek Ware”, and a few more little goodies, that I am sure you will be able to read about over at A2Central.
