Building the Diablo 2315 Archiver circuit board

CIRCUIT BOARD ARRIVED - THANK YOU PCBWAY.COM

PCBWay.com offered to sponsor the production of the main printed circuit board for my project to archive the 2315 disk cartridges containing software and data from IBM 1130 systems. I used a Diablo model 31 disk drive with standard density heads, which is compatible with the 13SD disk drive built into the IBM 1130. 

The shipment arrived today, securely packed, shrink wrap sealed with a desiccant packet. I opened everything and inspected my new PCBs. I chose to make these four layer boards with a blue solder mask and white silkscreen to give it an appropriate color scheme for the retro computing systems whose data I was archiving.

Well made attractive blank PCB

Protected in the box

Sealed with desiccant packet

PURPOSE OF THE PCB

This board plugs into the top of a Digilent.com Arty A7 FPGA (Field Programmable Gate Array) board which is where the logic and memory resides that will drive the Diablo 31 drive to read the entire cartridge and then upload it over a USB serial link to a program that build the file image on a PC. 

The PCB regulates power, producing both 5V and 3.3V rails from the input 9V supply, feeds the input 9V unregulated DC to the FPGA board, and delivers the two regulated rails to the circuitry on the PCB. I has an IDC-50 connector where a cable from the Diablo drive is plugged. Resistor networks provide termination of the incoming Diablo signals as well as transistor drivers to create the control signals out to the Diablo drive. 

Since the Arty A7 board uses a Xilinx Artix A7 FPGA chip with 3.3V LVCMOS input-output pins, I placed 74LVC125 buffer chips between the Diablo and the Arty A7 to shift the voltage levels from the 5V DTL signals of the Diablo to the 3.3V levels for the FPGA. The transistors that drive the output signals serve a similar purpose, controlling the base of the transistor with the 3.3V output of the FPGA and controlling an output line pulled up to 5V or sunk to ground by the transistor. 

INSTALLED THE COMPONENTS AND CONNECTORS

I had already bought or collected all the components to go on the PCB, thus as soon as I got to the workshop I began the assembly. I chose to solder on the resistors first, then the transistors and buffer chips as they were all surface mount. Next came the voltage regulators and their capacitors. At the end, I installed the various pin headers, the IDC-50 socket and the barrel connector for the 9V wall-wart that powers the assembly.

I did run into a snag - I had somehow ordered a 1.27mm pitch 50 pin socket instead of the 2.54mm IDC type. I searched the shop and found a breakout board that could donate the correct socket - to be replaced when I get the correct socket in the mail. 

Oops

Yanking this off the breakout board

FITTED THE PCB ONTO THE ARTY A7 BOARD AND CONNECTED THE DIABLO CABLE

The PCB has pins on the bottom that fit into the connectors atop the Arty A7 board, giving access to the input-output pins I was using for the archiver. It also supplied the FGPA board with 9V for its power. I discovered one mechanical issue - the Ethernet connector on the Arty A7 board is higher than the input-output pin sockets. It causes my PCB to be tilted rather than inserting flat above the FPGA board. The solution was to remove the Ethernet connector from the FPGA board. 

The cable from this board to the Diablo is a 50 pin IDC-50 male to male ribbon cable, the type used for internal SCSI drives in earlier PCs. That cable runs to an adapter PCB I built that routes the signals from the IDC-50 connector to an IDC-40 connector (the type used for internal hard disk connections in earlier PCs) which is what was on the end of the Diablo produced signal cable. 

The Diablo drive has a ribbon cable that ends in a male IDC-40 connector, which plugs into that adapter PCB that I whipped up. It is a small simple board that allowed the two sockets to be connected in the pattern necessary to route the signals, with a good ground plane assuring signal integrity. 

At this point, the hardware for my Archiver is all complete - I have the Diablo drive with its connector and terminators installed, the power supplies to power the Diablo drive, the archiver assembly I just built and the 9V wall wart to power the Archiver. As you can see, the FPGA board powers up and gives reasonable status. Once I get the heads installed and aligned in the Diablo drive, and the drive tested to be sure it works properly. I can start the archiving process.