Monday, October 30, 2017

Still chasing phantom issues probably connector related in HP 1000, suffered disc head crash


HP 1000 Processor

I have a feeling that flaky connectors are an issue in some of the erratic behavior I am seeing. I removed the floating point unit, reseated everything and checked the power supply output. Once I reseated it, the system ran through the floating point processor, scientific instruction set and fast fortran program tests (FPP/SIS/FFP) much better.

The diagnostic stopped on one error in the fast fortran routines, complaining that the .SETP operation was not interruptible during parameter fetch. This was the only error otherwise it completed just fine. Further, it passed that particular test fine a second time. This could have as easily been an interrupt failure from the HP-IB controller card it was using to force interrupts.

I reassembled everything, all IO cards and cables, then attempted a boot of the tape diagnostics again. Alas, my erratic problem where the tape can't be read by the boot loader has reappeared. This has to be limited to the tape drive, cables, tape controller card or some aspects of the basic processor function (less likely).

I pulled the tape cables, reseated the boards and reinstalled the cables, in an attempt to restore proper operation. It didn't work. Will get back to this tomorrow.

7906 Disc Drive

After more cycles of spin-up and plenty of time with the blower forcing out any dust, I let the drive complete a spin-up and drop the heads. I didn't hear anything but my nose detected a burning smell so I switched off and inspected.

Head crash on the top platter of the removable cartridge! I didn't both to look at the other surfaces or the fixed platter below because this is already a show-stopper for me. I only had the one removable cartridge. The platter is cut in a nice thin circle down to the aluminum substrate.

Scratched top platter of removable cartridge
Hard to see scratch on top of fixed platter
If I am to run RTE on the system, my options now are restricted to attempting to find another drive and cartridge or to engineer an adapter to use solid state or modern disk drives in lieu of the 7906. This will take some time and effort.

2645A terminal alternate characters

Marc and I are working to build PROMs to use with the display enhancement board. We do have good examples of the existing character sets from a fully populated such board, which we plan to read and burn onto new PROMs.

The challenge is to select appropriate chips, since HP has not identified the type of chips used. Further, they make use of a very unusual PROM chip that we have never seen in the wild - 1024 words of 9 bits each. Not for every character set. Most use 1024 x 8 bit chips but any 'microvector' character sets require the mystery components.

ROM socket - 8 or 9 bit data path depending on chip and contents
The PROM socket and wiring is compatible with the Signetics 82S181C TTL Bipolar PROM, which works at the proper speed and source voltage to handle the regular character set PROMs. It is not going to work as the 1024x9 part necessary for microvector character sets.

I found a surface mount EEPROM, National's NM27C210, which is 5V, fast enough for the job and has more than enough capacity. In fact it is a 65536x16 component, which is sufficient to delivery 9 bits of the 16 for 1024 of the 64K addresses.

The plan would be to build a small PCB the size of the regular 24 pin DIP socket used for the Signetics part. The NM27C210 would surface mount on the top and the board would route the signals to pins soldered through the board at the locations of the holes in the socket below. It would provide zero bits for the high order addresses and handle the enable lines from the socket to produce the relevant signals for the new chip.

We would need to work out a jig or fixture to program the chips, probably by providing small additional pins sticking up through the top of the PCB to feed the address, data and control signals for writing to the chip before it is plugged into the HP display enhancement board. 

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