ZERO PROGRESS AT THE FAB BUT QUOTED FOR 4 DAY BUILD
It is the end of Monday in China but my PCB has not progressed at all since the end of Friday's state - inner layer traces only. The order lists a four day build thus it must be completed and ready for shipment by the end of tomorrow - I expect rapid movement through the steps. It only
DECONSTRUCTING THE CURRENT EXTENDER BOX TO PREPARE LEADS
My new board design has screw terminals where each of the 82 signal wires will be attached. The current design has boards where 12 'receive' signals were attached, and other boards where most of the 'send' signals were attached, nested in a mass of cabling. I began to detach the wires coming from the 160 pin SAC connector in preparation for their connection to the new single PCB.
I beeped out each wire as I detached it and affixed a label with the FPGA connector pin it would eventually reach. I will end up with 82 labeled wires and all the boards dumped in the trash bin. As of Sunday I had most of the receive lines removed and labeled. Today I will work on the remaining receive lines and all of the send lines.
The FPGA board was detached from the ribbon cables and is ready to plug into the new PCB once it is built.
STUDY OF THE LED PANEL OF THE NEW CASE
The case I bought for this project had a small board on the front featuring three green and one red LEDs. I designed the new box to use these to display some status. The green LEDS will indicate when power is active in the box, when the IBM 1130 is powered up, and when the billing meter of the 1130 is running. Basically that last state represents when the machine is not idle. The red LED will light when the 1130 detects a core memory parity error and stops.
I tried to verify the voltage drop of the LEDs using my VOM but it failed to detect the diode junction in either direction. The back of the mini PCB holding the LEDs shows a diode symbol with the polarity indicated, with nothing on the board except the LED units. It was puzzling. I hooked up a 5V source and a suitable load limiting resistor but didn't see light from any of the four LEDs.
I then connected one to a variable power supply and did indeed see light emitted but at fairly high voltages. At this point, I believe the LED units have a load limiting resistor built into them, based on the way they behaved at varying voltages.
When I dropped the load resistor to 50 ohms, the LED would light with less than 4 volts signal, very suitable for my purposes. I was loathe to remove the resistor entirely - don't want to destroy the LEDs since they are not simple widely available types I could purchase.
I will do some measurements of the actual current draw with the 50 ohm resistor at a few voltages in order to work out an equivalent diode drop and load resistor value. I need this because one of the four LEDs will be powered by 24VAC rather than 5VDC. I need a suitable resistor on the board for that LED to produce the same current and light intensity.
CHOOSING MOUNTING LOCATIONS AND MARKING CHASSIS FOR CUTTING
I selected the location for the main connector and the new PCB, inside the case I will use. I have to finish selecting locations for the USB connector, the 1130 power connector, the main power cord and the extra signal connector I use for my SAC enhancement to control interrupt levels 0 and 1.
With those chosen, I will mark up the case so that the openings can be cut in the steel box. The cutting itself is likely to take place at the Melbourne MakerSpace.
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