[GreenKeys] [External] Opinion on toasty ceramic resistors

[Anthony Watson]

Wow, that’s interesting!  I’m pretty convinced I panicked while they were gassing off some lubricant that went out of bounds - just wasn’t an obvious pool or anything. 

But your story does give me ideas to check the current draw and make sure I don’t see any shorts around the motor that might be making these any hotter than usual. Can’t hurt unless I test with my fingers!  

But if I’m avoiding a slow lava flow versus a pyroclastic event. Ha ha

Anthony 
WB7PZZ


Sent from my iPhone

> On Dec 3, 2024, at 8:02 PM, Jones, Douglas W <douglas-w-jones at uiowa.edu> wrote:
> 
> 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
> <image0.jpeg>