Thanks for sending the manual, interesting! I don't think you can connect this counter to X2 directly. It won't oscillate. Are you using the EXT input or the TTL input at the back?
But, is there any way you can, with another M100, confirm that you can measure 2.4576 MHz on pin 37? To me it feels like there is a ground issue, or something. The fact that this machine does start some times, suggests that you should be able to get the counter connected and have M100 running, at the same time. I have a bag of 4.9152MHz crystals, if you need one. The other way to measure clock is to connect to pins on the system bus. Pin 15 is buffered clock. On Sun, Oct 18, 2020 at 7:37 AM Charles Hudson <clh...@gmail.com> wrote: > Stephen wrote: > > " > > * between 37 and ground you should have clock for sure. > * If I were you I would confirm that your frequency counter reads the > correct result when the M100 is working. > * not sure how your counter works.... > > * X1 is for the RTC, won't prevent start up > * X2 is the 4.9152 MHz crystal. > > " > I repeated my tests with the frequency counter, first verifying its > operation by connecting to a known-good source of oscillation (Velleman > PMK147'1). While connected to X2 with power on the frequency drifted from > approximately 60 Hz to about 135 Hz, up and down. With power off the > frequency returned to 0 Hz. I moved the counter contacts to pins 20 and 37 > of the CPU. With power on I got 0 Hz. > > I will try replacing the X2 crystal next. > > -CH- > > Link to counter manual: > https://drive.google.com/file/d/1Qpj-rVU-FyOG4KIyBXnG977CGlm0duFU/view?usp=sharing >
