[ih] Panel lights as a source of computer failure

[Scott Bradner]

fwiw - I created the printer circuit layout that substituted LEDs for at least some of the IMPs
for Bill Barker

and I was told that the "send a tech" went way way down from the once a week that it had been

Scott

> On Aug 21, 2025, at 3:39 PM, Alexander McKenzie via Internet-history <internet-history at elists.isoc.org> wrote:
> 
> Steve Crocker suggested that re-engineering the panel lights on the IMP
> raised reliability from 98% to 99,98%.  That's not the only fix implemented
> to up the reliability, but it was a significant part.  The whole story is
> in the article "Seeking High IMP Reliability in the 1970' ARPAnet" by
> Walden, McKenzie, and Barker, published in Vol 44, No 2 (April - June 2022)
> of IEEE Annals of the History of Computing. The panel light problem was
> specific to the second-generation Honeywell-316 IMPs; the original
> Honeywell-516 IMPs did not have this problem.
> 
> Cheers,
> Alex
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