IBM 1403 PRINTER WORK
For most of the week I was on the east coast, not able to work on the 1130 project, but I did get a bit done from Friday evening onward. The wiring on the controller board was tested, cleaned up and some testing was done. I feel pretty good about the code in the Arduino and have been exercising many boundary and error conditions to confirm that it is protectively testing conditions and handling issues robustly.
I ordered a box of full width continuous forms for the printer and a new ink ribbon. Both arrived during the week and were installed on Saturday. I did a test print to verify the quality of the printing across the long line size.
I completed some more of the serial link handling logic in the fpga, but still have to finish the other side of this logic, the part that transfers what has come to the 1403 adapter module as well as accepting print characters from the 1403 adapter and routing them out the link to the Arduino. This is modularly implemented to permit me to test and debug the link handling before I work through the printer emulation and 1130 memory interface portions of the design.
BOUGHT TYPEBALLS IN HUNT FOR PERFECT MATCH TO 1130 BALLS
I picked up two typeballs that seemed close to the 1130 style, advertised by their number only, but they are not a better fit than my current ball. They were in the PTT/BCD format rather than the correspondence (typewriter) arrangement, which is why I bought them. Probably used with a 2741 terminal or one of the variants used in airlines, banking and other applications many years ago.
I saw another 'unknown' typeball on ebay that appears to be identical to one of the two I just bought - it does not list the number nor show enough of the ball to be definitive, other than it is clearly PTT/BCD and the portion that is visible exactly matches the ball I just received.
I am still seeking two balls that are the exact versions used with the 1130, one for APL/1130 and the other used as the normal console printer font. I need the APL type or I won't be able to run APL/1130 on the machine. The other ball is desirable solely to gain the last 1% of fidelity between my replica's behavior and a real 1130 system, but I could easily live without it.
I own a ball that is very close to the latter, the difference is in the lower case letters. My typeball has lower case versions of the letters on the lower case side of the ball, but the 1130's typeball places upper case letters on both sides. Regardless of whether the ball is shifted or not, you see a capital letter typed. With the ball I own, it is possible for a program to print a mix of lower case and capital letters, whereas the same program on an 1130 would produce only upper case letters.
I even emailed somebody who owns a 988 APL typeball, asking if he would consider selling it, but he isn't willing to part with it. I found that person online, hunting down the address to message him, when I came across the image of the typeball on an image repository. I threw out some inquiries on other forums - one for selectric typewriter fans/collectors and another for the 1130 fans.
IBM 2501 CARD READER FINAL TESTING
The rebuilding and rewiring of the interface proceeded slowly, very slowly and carefully. Once the wiring was complete, it was essential to have all the boards installed in the enclosure to be solidly anchored, to allow for reasonable serviceability and to enable diagnostic tracing of signals without disassembly.
The last step is the connection of power to the various boards from the huge filter capacitors I added to the enclosure to minimize ground bounce and supply rail sag due to resistance in the wires within the unit and on the long-ish run from the 1130 out to the reader.
Bring up is proceeding well. Most functions and signals appear to be working correctly, although there was a loose ground causing bouncing of switch signals when I tap the enclosure. That was quickly found and corrected, at which point I had an interface that seems free of the glitches and mechanical sensitivity.
Row 8 and 9 signals are not the same as the other 10 rows - I am tracing signals and validating wiring to fix this. I will be verifying the error, mock and hock signals, all of which are in the same areas of the input distribution, latch and input one boards. A bit more testing to ensure everything is ship shape, then I can restart the system level testing of the card reader adapter.
HELP GERMAN MUSEUM RESTORING AN 1130 SYSTEM
I was put in contact with some people restoring an 1130 computer in Germany.The machine they received was missing a key circuit card, which controls four bits of the storage address to the core memory unit. They were looking for a spare card of that type or a schematic that might allow them to make a substitute.
None of the documention I can access covers this card, which was designed specifically for 1130 systems with memory configurations larger than 16K words. However, most of the card is built with discrete components, transistors and resistors, with just one ceramic SLT module on the board. From the ALDs for this card and other documentation I have, it is clear that the module is only doing voltage regulation/limiting. This is done many ways in SLT, many of which are documented with schematics, so I believe that an equivalent circuit could be defined with what we know already.
Three of the same type of board are in the machine already - driving the other address bits - and can be a reference sample to fine\ tune the replacement card, adjusting the component values until the operation, switching thresholds, delay and other characteristics are similar enough that the substitute card can be confidently used.
If I can get a higher resolution picture, or closer pictures of the card type they have to duplicate, I can identify the transistor types using the IBM code on the can, as well as picking up the resistor values. The SLT ceramic module has a code that will also give me the precise circuit configuration and specifications of what is inside. I need the museum to respond with the pictures before I can draw up the equivalent circuit.
I have to wait for my offer to be passed back through a chain of people by email before I can communicate directly with the institution, but in the meantime I have collected some material and prepared what I would need to assist them.