>The relay used had a very high duty cycle, as it
>was used for on-hook and pulse-dial..

I suspect this was the real reason for the failure, effectively the pulse
dialling exceeded the repetitive surge current rating, causing the diode to
fail. The only ones that failed were probably close to the min spec limit,
with most devices having enough margin that they do not fail, although on
the basis of the failure rate, one would possibly need to look at long term
reliability.

>This was a solid fix in my view, and no later
>failures with the TVS's were ever passed to me.

And I do not think anyone can fault this fix.

I suspect that most of the discussion has resulted from TVS devices being
perceived (probably without foundation) as harder to find, and potentially
more expensive. In this instance I feel the extra expense (if any) could be
justified, and certainly the time taken to source the device is justified,
and would certainly justify changing new build to fit the TVS instead of a
diode.

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