[GreenKeys] [External] Opinion on toasty ceramic resistors

[Jones, Douglas W]

From: Anthony Watson -- Tuesday, December 3, 2024 2:43 PM
>  I have never had ceramics fail, and these aren’t failed - just look well toasted.

I remember back in 1974 when I was a student at the U of Illinois, we had an interesting ceramic resistor failure.

Well, it didn't quite fail.  It did melt and drool molten glass on what was under it, but it continued to resist at its rated value.

Full story.  We had a PDP-11 system, with punched-card reader and line printer, used to run student jobs.  It had a fixed head disk for fast access to commonly used programs and scratch files, and DECtape for the rarely used stuff.

One day, the disk failed.  The DEC technician came to do his thing, and on opening the case, he found two problems:

1) The disk heads had worn neat grooves all the way through the oxide on the platter.
Fix:  We only had one side worth of heads.  The other side of the disk was virgin, so he flipped the disk over, went to Kmart for a can of Turtle Was, carefully waxed and polished the unused side of the disk, and re-assembled that part of the problem.

2) The resistor melted because of a bad motor-start relay.
Fix:  Replace the relay.  No need to replace the resistor!  Chip the glass drippings off from below the resistor.  Fortunately, what they fell on was structural, not electronic.

When he left, everything worked, and continued to work until the end of life of that machine.

             Doug
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