Scott, if you have a scope that will be extremely helpful. In my experience you can sorta tell when the CPU is booting, and has access to RAM and ROM, by looking at the signals on the bus. I typically check out the signals at the main ROM first, then go to the nearest RAM. Those parts are at the "end of the line" for the address/data bus, so if you have an open trace, you will see it there.
If the Main ROM and 1st RAM have good signals, it should boot. Also worth it to check that the CLK signal on the 8085 is showing 2.45 MHz. I also check /RD, ./WR, IO/M etc. good luck, and ask questions. Steve On Thu, Dec 17, 2020 at 11:30 AM mcdonnell.junk <mcdonnell.j...@comcast.net> wrote: > I am an electrical engineer. That doesn't mean I am an expert in all > things (or even a lot of things), but my home lab is very well equipped > with various scopes, logic analyzers, eeprom and various other programmers, > an eeprom emulator, processor emulators, hot air rework station, electrical > desoldering pump, microscopes, hakko temp controlled irons, etc.... and at > work I have access to pretty much anything. > > The problem is sometimes my impatience, not knowledge. :) > > Point is that I do have the right tools and experience to work on this > stuff. But the M100 is a new computer for me. I was a Commodore kid. > > If I break traces, I am not freaked out by that. I can repair them > properly. Of course, I would rather not! > > Power supply rails were fine, btw. Of course that doesn't mean previous > owner didn't plug in 12V or reverse polarity adapter and just didn't tell > me. I bought it broken along with the working unit. But power supplies are > stable at the moment. > > Scott M. > > > > Sent from my T-Mobile 4G LTE Device > > > -------- Original message -------- > From: Josh Malone <josh.mal...@gmail.com> > Date: 12/17/20 9:18 AM (GMT-05:00) > To: m...@bitchin100.com > Subject: Re: [M100] Model 100 Repair - Keyboard not responding, LCD > missing a column > > Sorry for not chiming in yesterday. Before taking the soldering iron to > anything, it's good to always check the power supply rails for proper > voltages and remove the optional RAM modules (as I see you have done). What > sort of tools do you have available? (oscilloscope, multimeter, > temp-controlled soldering station) Given the age and relatively cheap > construction of these machines, it's very easy to do more damage when > trying to repair them. > > -Josh > >>