Changes

The semester began with the digital control board prototypes sitting on lab bench waiting to be tested. My job was primarily to design the boards, not to debug them, though I still played an integral part in the testing process. We were all relieved that none of the boards appeared to smoke immediately when we first applied power, though there were a few confusing problems that had to be sorted out. Most of these problems are described in detail on the [[Digital control board debugging notes]] page. More or less, we had to solder a pin that wasn't connected, replace the crystal oscillator with a CMOS oscillator, and rewire few traces that were accidentally connected to pins intended for other signals. I won't repeat all of the changes we made here since it would be redundant to the page that already discusses it, but the important part is that we have one board that is fully operational, and the version 2.0 schematics/layout reflecting all these changes are complete. I anticipate that production of the version 2.0 boards will occur at the beginning of the spring 2010 semester.  

The semester began with the digital control board prototypes sitting on lab bench waiting to be tested. My job was primarily to design the boards, not to debug them, though I still played an integral part in the testing process. We were all relieved that none of the boards appeared to smoke immediately when we first applied power, though there were a few confusing problems that had to be sorted out. Most of these problems are described in detail on the [[Digital control board debugging notes]] page. More or less, we had to solder a pin that wasn't connected, replace the crystal oscillator with a CMOS oscillator, and rewire few traces that were accidentally connected to pins intended for other signals. I won't repeat all of the changes we made here since it would be redundant to the page that already discusses it, but the important part is that we have one board that is fully operational, and the version 2.0 schematics/layout reflecting all these changes are complete. I anticipate that production of the version 2.0 boards will occur at the beginning of the spring 2010 semester.  

There is still one lingering problem with the digital board design that has not yet been resolved, however. Even after all of the version 2.0 changes were implemented on the version 1.0 boards, only one of the three boards produced actually functioned properly. For a reason unknown to us, two of the boards ended up with their digital to analog converters burning up and smoking. We thoroughly reviewed the schematics and the layout, and found nothing miswired. Furthermore, we analyzed the placement of the ball grid array DAC to the best of our ability, and determined that a misalignment of balls is not the cause of the failure. All of our power supplies are stable, properly decoupled, and grounded as called for by DAC's manufacturer. Currently, the best hypothesis for the failure of 2 of the 3 DACs is that one or more of the absolute maximum ratings must have been exceeded at some point during the assembly process. Analog Devices lists fairly specific specs with small tolerances relating to maximum temperature and the length of time which the DAC may spend inside a reflow oven. We have run into some difficultly trying to find out from the boards' assembler whether they followed the published specs for the assembly process, but we intend to keep trying until the cause of the DAC failure has been resolved.

There is still one lingering problem with the digital board design that has not yet been resolved, however. Even after all of the version 2.0 changes were implemented on the version 1.0 boards, only one of the three boards produced actually functioned properly. For a reason unknown to us, two of the boards ended up with their digital to analog converters burning up and smoking. We thoroughly reviewed the schematics and the layout, and found nothing miswired. Furthermore, we analyzed the placement of the ball grid array DAC to the best of our ability, and determined that a misalignment of balls is not the cause of the failure. All of our power supplies are stable, properly decoupled, and grounded as called for by DAC's manufacturer. Currently, the best hypothesis for the failure of 2 of the 3 DACs is that one or more of the absolute maximum ratings must have been exceeded at some point during the assembly process. Analog Devices lists fairly specific specs with small tolerances relating to maximum temperature and the length of time which the DAC may spend inside a reflow oven. We are currently working with the assembly company to attempt to determine exactly what caused the failure. They plan to reexamine the DAC BGAs on heir x-ray machine, and also perform other testing to determine if the assembly process caused the failure.

==== Amplifier Board ====

==== Amplifier Board ====