Thanks for the response concerning the 40H parts.
I took some time this evening to very carefully look at all the signals on the 80C55. I thought I saw some odd waveforms and after setting the scope to single shot mode I did indeed see some oddness on AD0 through AD7. Take a look: https://1drv.ms/u/s!AtH4vpaZnzX7j8A29GFkjLbQlWpLUA I checked that it is the same at the 80C55 side of M1 and M2 while the ‘other’ side of M1 and M2 has nice square waves. I then checked that the control signals ALE and /RD appear to be correct and they do. This leads me to believe that one or both of M1/M2 are defective. I believe I have a 74HC version of these on hand. I very much appreciate being steered in the right direction 😊 On an unrelated note: what kind of evil flux did they use on these boards. I tried to clean the flux off of my capacitor installation and wound up taking 30+ minutes to flush the back side of the PCB with alcohol several times to get the yellow tinged flux off. It wanted to form a nasty white chalk type coating. Thank again, Jeff From: M100 <[email protected]> On Behalf Of Josh Malone Sent: Tuesday, May 1, 2018 5:46 PM To: [email protected] Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 I replaced my 40H decoder with a 7x part and have had no issues. The address decoder circuit failed in my 102 and it turned out to be the demultiplexer / decoder. On Tue, May 1, 2018, 4:57 PM Jeffrey Birt <[email protected] <mailto:[email protected]> > wrote: Possible silly question…I have been able to find no data on the 40H244, 40H245, 40H373 part numbers. Given their function and pinout I’m guessing that a 74HC part would be an acceptable substitute? Thanks again, Jeff From: M100 <[email protected] <mailto:[email protected]> > On Behalf Of Fugu ME100 Sent: Tuesday, May 1, 2018 9:26 AM To: [email protected] <mailto:[email protected]> Subject: Re: [M100] SPAM-LOW: Re: New member - question on 'half' alive Model 100 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.
