Thursday, June 25, 2015

Bit of work after I return from biz trip - still a draw between Pertec and me

I am back from a multi day trip to the east coast on business. While there, I visited the Techworks in Binghamton ( where I met a few of the restorers and looked at their 1440 system with 1442 card reader/punch, 1311 disk drive, and 1403 N1 printer. It is mostly working, just some remaining erratic console printer behavior (yes, another 1053 mechanism with its dreadful old grease causing problems), and issues getting the card reader working.


I swapped about 15 tantalum capacitors out from the servo board, which has all the power regulation circuitry as well, plus replaced the 56 ohm precision resistor for the -5V regulator. It is a very hot day so my tolerance for working with a hot soldering iron and a hot desoldering iron under those conditions is limited - I do a burst of 6 to 10 component swaps then walk inside for a cool-down.

By late afternoon, I attempted a measurement of the voltage levels, now that I have replaced the resistor and cleaned up the capacitors. When I fired it up, the replaced 56 ohm resistor emitted quite a nice stream of smoke and charred itself up. Working hypothesis is that the resistor failure is a result of some other component problem, and shouldn't be replaced until I sort out the underlying cause.

I tried to check the components in the -5V section while mounted on the PCB - not perfect but looking for anomaly not explainable by the circuit schematic. I removed a couple of components to test them out of circuit, but they weren't defective.

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