Hi all, hope you are all well as can be expected?
I've had a problem with one of my 800Xls with the dreaded Red Screen of Death.
Andy was kind enough to let me borrow his syscheck II 2.2 board which initially didn't seem to help as I still got the red screen.
So I started on fault finding using Atari's 800XL Field Service Manual Rev 2.0 checking U2 - U5, U18, U19, U28, and U29. (By the way, U4 and U5 are reversed in the parts list).
All the 40 pin chips GTIA, Pokey etc. are known working items, along with the Basic and OS chips, as these had been checked out in another working 800 XL. All the RAM chips were checked too. This just left U18, U19, U28 and U30, which were soldered into the board.
U18, and U19 were de-soldered one at a time, and checked in my programmer for correct function. Both had sockets added to the board, and the offending item at this point was U19 the 74LS14(Hex invertor). I suspect a dry joint(s) on he chip.
Using syscheck, the 800XL ran through its memory check and passed. It did not pass the OS checksum test.
That's strange as the OS chip is known to be good. So I re-soldered the socket and no change. Time to replace the socket, and after that it passes all checks no problem.
The socket I removed had broken pins on it, which I've come across in the past.
This computer had been sitting around for over a year after an earlier fault finding attempt.
So another 800XL lives to fight another day.
The second 800XL had the Black Screen of Death.
This one turned out to be a right pain, as the S yscheck reported U9 and U13 RAM chips. These were removed and socketed and replacements fitted. Syscheck was rerun, reporting all RAM chips at fault. The removed ram chips were tested in my stock 800XL and worked fine.
The problem was traced to the MMU, which works fine in my stock 800 XL but not in this computer. MMU's swapped over and all is happy.
One more problem the keyboard isn't working so that is the next task to complete.
Two almost down, one to go.
The power supply needs a new plug fitting at the drive end, and the internal fuse replacing. I've got the replacement parts so will update you when it's been completed.
Photo 1 - new plug.
Photo 2 - fuse holder with added heat shrink sleeving.
Photo 3 - Transformer and fuse holder fitted prior to the bottom plate being refitted.
The 810 PSU is up and running.
I have now used the repaired power supply for about 20 hours, and so far and it working with no problems. The body is nice and cool, so this is another piece of vintage computing saved from the recycling centre.
Stay safe everyone.