[Oberon] Updated RiskFive FOM schematics

Skulski, Wojciech skulski at pas.rochester.edu
Tue Jan 16 17:48:08 CET 2018


thank you for the comment.

> These days, my first concerns with any new electronic machine is
> reliability and repairability.  Too many gadgets are built with poor
> quality, barely in spec. components, surface mounted.  

Use a reputable manufacturer with proven track record. Manufacturers are not equal. Some do lousy work, some do excellent work. A well assembled board is very reliable. 

> After a few years a board fails.  

While anything can fail, this statement is generally not true. It is only true statistically. 

> There is no straigthforward way to identify the
> failed component.  Replacing a surface mount component is tedious and
> error prone.  Replacing a many-pin device just to find whether it is
> faulty is too time consuming.

High reliability boards can provide board diagnostics. For example, my most recent 40-channel digitizers monitor all the currents and voltages on board. We will record a database of monitoring results over the course of our underground experiment, which is five years. 

Less critical boards, like RiskFive, do not provide such extensive monitoring features. However, you can monitor internal FPGA voltages and the temperature, using its built-in ADC. The appropriate software needs be written, of course. You can then project an imminent board failure, if the FPGA temperature raises for no good reason.

> Conclusion: a board with components mounted in sockets and through
> hole soldered would have much more appeal than fragile components
> surface mounted.  Perhaps simply not feasible in our world and I
> should forget modern electronics.  No offense intended.  Just an frank
> comment.

This conclusion seems logical, but it is wrong. Sockets do not provide the bandwidth which is required by modern interfaces. A standard ball grid array (BGA) pin can operate at over 1 gigabit per second per pin. Special mutligigabit transceiver pins (MGT, which I am not using on RiskFive) can operate at gigabits per second, as the name suggests. A socket pin can provide a couple hundred megabits per second at the best.

The modern surface mount technology was developed for a reason. I suggest reading the following reference to clear the confusion. It is available from Amazon.

"High Speed Signal Propagation: Advanced Black Magic" by Howard Johnson and Martin Graham.

Thank you,

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