Success with the bench testing of the 1130 MRAM memory board finally

FINDING ROOT CAUSES

I have been plagued with erratic results, non-repeatability and other challenges in what should have been a straightforward verification of the correct operation of the memory replacement board. I began to suspect that the bench testing apparatus was causing these issues, not the board or its components. 

The Arduino had 16 data outputs and 13 address outputs that had to be connected to my board, in addition to the control signals that drive the read and write operations. For each of those lines, there was a male pin on my board and a female socket on the Arduino, which I connected with a M-M jumper plus a F-F jumper to change the gender. That means 3 connections for each of the 29 lines, none of them mechanically secure. 

I also used alligator clip jumpers and pin jumpers to connect grounds between the Arduino and my board as well as connecting to a breadboard where I had the pullup resistors for the sense output lines of my board. The Arduino ground is just a few pin sockets. I believe that slight vibrations were causing noise or corrupting signals as this setup was just too fragile to trust the results. 

FIXING THE ISSUES

The writing program was changed to perform a read back of the address right after the write cycle. I pulled all the address lines off as I already know it was correctly addressing memory, thus all further testing was done just with location 0. That eliminated 13 signals and 39 connections. 

I moved the 16 data connections from the Arduino to the breadboard and set it up so that a slide switch would set the data to 0 or 1. The Arduino was only emitting the Storage Write and the Storage Read control signals now. 

TESTING RESULTS

I was able to verify that all 16 sense output lines were producing the data that I had just written, reliably. I checked the checksum output lines as well and verified that they were giving me the pulses needed to achieve odd parity on each 8 bit halfword coming from memory. 

I am now satisfied that this works properly, so that I can attach it to the 1130 system and test it there. 

The board above with its bodge wires and the outboard voltage regulator module needs conformal spray and then a metal can placed over the MRAM chip to reduce stray magnetic fields that might change the data stored on the chip.