Saturday, July 4, 2015

Desoldering station working, not so much the ztex board, and continued progress with the P390


I continued to fiddle with the DOS/VS boot-able utilities, to figure out why it didn't like the 3350 disk drive I was trying to initialize. I expended the card images in the hope that my problem was due to short card images. Same error. I am now left to believe that the lack of alternate tracks on the emulated disk is somehow flagged as a problem, or there is some other incompatibility between the dos standalone init program and the P390 emulated drive.

I am setting up a boot-able tape image of ICKDSF, the standalone format program, which will format the pack in the OS rather than DOS style. The only difference is that DOS does not use the type 5 record which records free space on the volume and therefore it flips on a 'DOS contamination' bit.

This change happens any time that DOS mounts a pack - the contamination bit is flipped on and the DSCB record is set to zero. If the pack is mounted by MVS, it recreates the format 5 record with an accurate free space count then resets the contamination bit. Therefore as soon as DOS restores the distribution image to the disk, overwriting the VTOC, it will have zero space and the contamination bit properly set.

I moved the P390 and monitor to a more convenient location inside the workshop, since my checkout (and playing around) is going on longer than I expected. I can now sit down with the monitor at tabletop height right behind the keyboard and mouse.

There are so many little details, commands and conditions to remember for each operating system - having to sweep aside four decades of mental cobwebs - but it is slowly coming back. I just remembered that I could 'punch' the standalone initialization program into the virtual card reader in a virtual machine, IPL that card reader to do the task. That means I wouldn't need to prepare the virtual tape image.


I poked around and found that the connections to the power supply transformer for low voltage for ICs were a bit intermittent. With a bit of manipulation I was able to restore the unit to operation and used it to remove my burnt op amp in the Pertec servo board.

With all the desoldering, the copper rings around the openings are gone and some of the traces arent close enough to take solder reliably. I put in an IC socket, to avoid this happening again, and then tested and restored connections as necessary to get this socket wired properly. It was tedious work but completed eventually.

While I am at it, I looked at all the other locations where I removed parts - all the tantalum replacements and the other fried op amp - to test every pin for full connectivity to the rest of the board. I was not done by the end of my worktime today.


I tried all the examples and demos in the SDK as a way of learning something about the problems I am having, but essentially all the demonstration programs load the bitstream to the fpga as the Java code on the PC starts, so that it doesn't matter if the fpga board won't boot up on its own. This masks the problem.

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