PDP-11/23 Debugging

Jon Elson elson at pico-systems.com
Sat Nov 8 15:22:37 CST 2014

On 11/08/2014 12:26 PM, Pete Turnbull wrote:
> On 08/11/2014 15:58, Noel Chiappa wrote:
>> So it turns out that loose wire-wrap pins seem to be a 
>> systemic problem on
>> 11/23's. I just discovered _3_ more on one single 11/23 
>> board - two of them
>> the pins for the master clock! I put my finger-tip on 
>> them and wiggled, and
>> they were loose.
> I've had dozens of those pass through my hands or at least 
> across my workbench and I don't recall ever seeing that.  
> But given your experience, it's clearly something to watch 
> for nowadays.  I wonder if it's exacerbated by the 
> wire-wrapping being done.
I'm guessing the problem was that the wire wrap pin had 
broken free of the solder
joint to the etched PC board?  My guess is more along the 
lines of frequent
board insertion/extraction fatigued the solder joint, as 
pushing the board in/out
does wiggle the pin just a little.  I haven't seen this 
problem either on DEC
stuff, but I can imagine it happening.  it might have been a 
batch of backplane
that was not soldered quite properly, either temp profile 
wrong or some kind
of contamination of the solder bath.


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