[sdiy] Reliability: Share your lessons learned

[Tom Wiltshire]

My own experience is from years of fixing stompboxes for mates and fixing dataloggers at work.

On the pedals, it's always the jacks, the pots, and the flying wires that give up. Actual electronic failures are much less common. But anything where a plug gets rammed in and out frequently is going to be a potential point of failure. Did I mention that I hate those stupid 2.1mm DC connectors too? Especially if they're soldered to the PCB - that's *asking* for trouble. Eventually the strains put on the socket will crack the solder joints and it'll stop working. I've seen this on the board-mounted jacks on my Pro-One too.

On the dataloggers, there were various things that used to give us problems, and mostly that was to do with temperature or temperature changes. One particular type of unit had a pair of boards stacked on top of each other with a 0.1pin header and socket row connecting the top board to the lower one. Although the whole lot was potted in clear resin and so protected from moisture, over time the expansion and contraction caused by temperature changes could cause this connection to fail. Bear in mind these boxes were stuck outside or down a manhole for most of their lives, so the temperature range was reasonably wide. The batteries were also a  common failure in cold weather, where the voltage would drop low enough to crash the uP and then it'd go into a high current draw state and flatten what was left of the battery. With decent quality batteries we expected a 10 year service life and many did better than this before they came back for a new one.
The inputs were protected by optoisolators and in general this was very successful, although I remember one unit that had been connected to something that had been struck by lightning. This was sufficient to blow the opto chip to pieces, even within the potting compound. Never seen that before or since!
The connectors on these units were all Milspec and consequently didn't give us many problems.

So, in summary:

Works:

	Electronics!
	Potting compound
	Milspec connectors (and probably other parts too)
	Optoisolation of inputs

Doesn't work:

	Mechanical parts!
	PCB mounting of commonly used jacks and connectors
	Cheap pots (although these are easily repaired)
	Batteries in cold weather
	Interconnection wires that aren't properly heatshrinked to prevent them snapping off

I'd have hoped I'd learned something more than that, but that is pretty much it. Sigh.

T.


On 15 Nov 2010, at 01:29, Mike Beauchamp wrote:

> The recent .1" heading thread has me thinking about long-term
> reliability. We all have experience building and repairing things that
> employ different parts, techniques and finishes and we've all seen
> what is still working and/or easily repaired.
> 
> So please share any lessons/experiences about what works and what
> doesn't for the longer-term.
> 
> 
> My experience is still rather limited and the stuff I've built hasn't
> been around for too long, but I suppose I can say:
> 
> works:
> -point to point wiring and eyelet boards. (more of a guitar amp thing).
> -PCB's with a silkscreen legend designed for others to see and understand.
> -PCB's with soldermask and cleaned after assembly. (I haven't tried a
> conformal coating yet)
> -socketed IC's
> -Alpha pots (and I like that they can be disassembled for future
> maintenance/cleaning).
> -neutrix and switchcraft 1/4" jacks.
> -electrolytic capacitors that are easily replaced.
> 
> doesn't work:
> -lots of hardware from futurlec (especially their unusable 1/4" jacks)
> -strain relief on most wallwarts.
> -particle board, MDF, chipboard, etc. (if there's a possibility of
> water contact.)
> -perfboard. fails way too easily when being repaired/modified.
> -the paint electro-harmonix used on my deluxe memory man reissue. epic fail.
> 
> 
> -- 
> [mike]
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