I guess it must just be the way those game (Engineering test files) files were saved on the website I got them from. I selected them for the test only because I recognized the .prg. Now I know about this it won't be a problem.
I've started on the Osborne/Donahue PET book, so that should help me.
I've moved to cleaning up the hardware, it is all in pretty good order. For the IC's in sockets I cleaned them and lubricated them with mx-3, mostly they were good though the occasional one had enough oxidation to possibly cause trouble. This computer has a paucity of sockets, compared to say the SOL-20, where the sockets can be very troublesome. All the sockets though are a good design where the claws grab the pins across the flat and all had good tension. The 4116 RAM IC sockets look like they were factory fitted, on the other hand, the 4116 RAM IC's are 1981 vintage, but every other IC on the board is 1979 vintage. The only non factory looking soldering is that two IC's on the board, of the 2114 variety UF7 & UF8, though one is an MCM21L14, were placed in sockets, and they had a blue dot sticker on the bottom surface by each socket, so maybe it was factory, but inspection shows they were once 20 pin sockets cut down to 18 pin.
On the bottom of the board it says Part No. 320350 Rev E. On the top it says Assy No. 320351.
All the electrolytic caps on the board test ok on the ESR meter so I'm leaving these alone. I have not got to the VDU yet.
Over the years, electrolytic caps have got a lot smaller. For example a modern 22,000uF 16 V cap is about half the size of the 1979 vintage 23,000uF 15V cap in the PET (that failed).
So I looked around to try to find a replacement cap that looks the part in the computer. ( I like the way vintage computers had gigantic caps in their power supplies) .To get a cap these days of the approx same physical size as a 1980 vintage part it is necessary to go up in voltage rating (which is ok). After some hunting I found the new manufactured cap (a Vishay part) at RS. So I'm going to fit this to my PET as the replacement. Not cheap, but you get what you pay for at least with a part like this. It is better to do this than buy a 1980's vintage part. This Vishay part is just a little shorter and same diameter as the original.