PDP-11/23 Debugging

Tothwolf tothwolf at concentric.net
Sat Nov 8 17:02:14 CST 2014

On Sat, 8 Nov 2014, Jon Elson wrote:
> 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.

It would have been hand soldered. Wirewrap pins can't be wave soldered 
since that would contaminate the gold or silver plated pins with solder 
(the solder would dissolve and strips the gold or silver from the pin).

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