I need some Smart People Help.
The IBM Model F keyboard has a little microcontroller in it, an Intel 8048. The 8048 has an internal oscillator, which you can configure the speed of by fiddling with the X1 & X2 pins.
The schematic is attached. I plugged some numbers into a formula and got ~5.1Mhz, but I'd just like someone who knows what they are doing to verify.
I'm intrigued by the handwritten '25pf' note. Is that a correction of the '10-15pf' figure? Why is 'C=10-15pf' off to the side, isn't it calculated based off the two capacitors used? I wish I had gotten an EE degree.
@gloriouscow From a quick glance + calculation I get 3.2 MHz for the 130 uH coil. The capacitors should be the same on XTAL 1 +2; I'd change the coil to get the desired frequency. If you can check what values were assembled in.
@gloriouscow If I plug the numbers in from above formula I get 3.2 and 5.6 MHz, respectively