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I got back at the project today and hooked up the floppy disk. But, I am now experiencing some odd behaviour with the keyboard. I get the H/D/M? prompt and pressing M jumps into the Monitor, however at this point essentially no other keys except '8' work. I swapped in the keyboard from my other C4P ...

I completed the schematic today. Please check your email.

/Jeff

Thanks, Phil

/Jeff

I must say, I really do find this forum useful! Even just using it to log my thoughts and steps.... It assists in refining the diagnostic process. I pulled up the C4P 540 schematic and noticed that the $D000 RAM for ID0-ID3 was U2C. Attached directly to its data lines was an 8T26, so I changed it wi...

I have done some further testing. I used the monitor (rather blind) and stored some values directly into screen memory. At $D444 I stored a $00 and got the racing car, and I also stored a $FF and got the NW facing tank. so I think the $D400 through D7FF video is working fine. At $D100 I stored a $00...

Well, victory was short lived. I decided to let the machine "burn in" for a while, and sure enough a new symptom arose. It seems there is now a video issue. I am not sure where to look, so I was hoping that your trained eye could suggest a direction to investigate. This is what is now on screen: Scr...

I bought the C4P that was listed on eBay. The fellow used to have a vintage computer collection but had to sell it off because of lack of space for it. It arrived on Saturday and I set it up on Sunday. It generated a screen of random graphics but did not respond to the Break key. I popped it open an...

I have emailed you the latest schematic. Feel free to post it.

/Jeff

Well as it turned out, I must have mixed up the old, bad IC with the new good IC. Fortunately, I bought more than I needed, so I grabbed 2 fresh ones, out of desperation and installed them. Now everything seems to work! I have used the Monitor to test all the memory from $1000 through to $BFFF in $1...

Yes, the C3 series had an option for either a 29MB or a 74 MB hard disk. Those were huge at the time. The "H" option used different boot code from the "D" option, since the hard drives were controlled by a different hardware subsystem from the floppy controller. Is there any information available o...