Saturday, June 27, 2015

P390 checks out and runs MVS, replacement op amp commits suicide, 1442 card reader news of the world


While I haven't made any progress on repairing or replacing the punch feed wheels for my card reader/punch, the National Museum of Computing in the UK, which has a restored 1130 system, has had great success in clearing up a problem they have been experiencing for months on their 1442. Congratulations to Peter Vaughan of TNMOC.

The team at the Techworks museum in Binghamton NY are engaged in battle with their 1442 reader/punch, although this one is attached to their IBM 1440 computer rather than an 1130 system. I wish them success as well.


I ran out and bought a new op amp and a few 10uf and 22uf tantalum capacitors, allowing the completion of the replacement of the failing capacitors on the servo board and an attempt to restore the regulated power supplies.

After putting everything back, swapping the suspect op amp and swapping out the 22uf tantalums, I fired up the bench test and saw an essentially perfect -4.98V level. Time to move back to using the main power supply, delivering -20, +20 and +10 raw power, plus hooking in the logic board and both heat-sink mounted sets of power transistors. If I find all four regulated voltages are good and the fuses hold, it will then be time to proceed forward.

Moving forward means that I have to re-install the three crowbar SCRs which will blow a fuse if the regulated voltages go too high. Unfortunately, the +5V crowbar SCR was bad and the replacement SCR I bought on ebay was also bad, so I left that circuit unprotected. Then, I hook up all the cables and boards and repeat the power testing to ensure I now will hold power at the proper levels and the fuse-blowing is far in the past.

Alas, when I fired it up, watching the +5V supply, I saw it soar to about 8V and saw a small wisp of smoke as my replaced op amp committed suicide. Something is still not right. This is not making me happy. I am putting far too much labor into this, given that this was an opportunistic buy and not something that is mainstream for the 1130 project.


My suspicion that the MVS wait state was due to a simple operational issue was confirmed - the wait state I received means that no console was available for the IPL to continue. I took a bit of time today to fire up the system again and try to figure out what I have to do to set up a virtual console terminal that MVS will find during IPL. This will involve starting at least one 3270 session.

When I started a TN3270 session as the P390 was booting, I  had a main console and was able to do a cold start boot and see MVS come fully up. I did some minor operator commands to poke around and convince myself I had a workable system, then quiesced for the day.

This P390 system is a normal PCI based x86 system plus the PCI card for the processor. Unfortunately, that means the parallel channel card I own, which is designed for the IBM MCA bus, can't be used to allow this to hook up via bus and tag cables to physical peripherals. I would need to find a PCI version of the parallel channel board in order to achieve that added functionality. 

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