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Floppy is still not tested, but it got quieter after a squirt of CRC lubricant and having been left on for a while.

Got a new regulator today, and replaced the dead one. Unconnected the leads before powering up. Tested the voltages, and all seemed good. Reconnected the leads and powered up the machine. The 4P looks to be working perfectly except for the keyboard, which I'll get to later. For the time being I'm us...

I think I have the problem with the power supply solved. The units are made be a company called Deltron, and have as one of their components a part called CA723CE. See here: http://www.datasheetcatalog.org/datasheets/105/109944_DS.pdf As these parts are socketed it was a no brainer to try swapping o...

Here is a pic of the two power units:
The non working one is on the right.
I will temporarily disconnect the power line to the backplane so that I don't accidentally put a crazy amount of power through the boards.

I can't say for sure, but I think it looks great!

Ok...I have some great news, some good news, and some not so good news. Firstly, between your vulcan logic brain and my persistence to track down a problem, we both guessed right. U5E was indeed the culprit. I desoldered the chip, dropped in a socket and a new 74LS163 that I bought today...the video...

No, unfortunately these chips are not socketed. Some are, but most are not. Fortunately I have a hakko desolder station

Thanks for the lengthy reply. I'm just racing out the door now, but I might have time to grab some 74163 and 74157 IC's on the way home a little later. Maybe tonight can pull out the scope and do tome poking around. Or I may just start by replacing U5G. I did try grounding pin 1 of UC3, but in itsel...

One thing I forgot to mention is about the variable resistor for tuning. When I was making my parts selection I saw there were a few different types with different leg configurations. Some had a triangular distribution and others had the legs in a straight line. I selected the one in a straight line...

Thanks for the reply. It's going to take me a little bit to digest what you wrote and understand it. As for your question. I believe that the screen is displaying more that 64 characters...probably more like 80+. See here: http://web.me.com/lord_philip/other_computers/OSI_4P_Fix.html Looking at the ...