If checking the buffers etc you should see the I0/M line toggle quite quickly after power on and of course the ALE line. If it does not then it is not even starting a proper boot, I feel your processor is OK they are quite robust and well protected by all the buffers.
I think you mentioned a click on power-on this could be the remote relay clicking on, it is controlled by M14, this too is a symptom of an improper boot sequence. This part also controls access to the ROM, if it does not initialize correctly the ROM might never be accessed properly. The chip ids look good to start. You may also want to check continuity to the ROM and RAM chips just to make sure there are no cracks in the Address and Data PCB tracks. The quality of the M100 boards is quite low. From: M100 <[email protected]<mailto:[email protected]>> on behalf of Jeffrey Birt <[email protected]<mailto:[email protected]>> Reply-To: <[email protected]<mailto:[email protected]>> Date: Tuesday, May 1, 2018 at 2:57 PM To: <[email protected]<mailto:[email protected]>> Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 Thanks that was very helpful. I’ll double check the A/D lines and all other pins on the 80C85 but as I recall they were all toggling nicely in the 0-5V range. I’m having to relearn how 8080’ish systems work. It is one of the first processors I learned on (well Z80 on a TS 1000) and then I got into the 6502 and really went to town. I’ll also try to determine if the AD buffers / mux are functioning properly. Unless I misread the schematic M1, M2 and M21 are the primary culprits. I also just noticed that the AL/E line runs though a buffer so I need to check that signal on both sides of the buffer as well. Thanks again, Jeff
