PDP-11/23 Debugging

Pete Turnbull pete at dunnington.plus.com
Sat Nov 8 18:21:59 CST 2014

On 08/11/2014 23:02, Tothwolf wrote:

> 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).

The "wirewrap" pins on the 11/23 and many other DEC boards are short 
pins that are accessed on the /component/ side of the board and used for 
jumper links, eg to select baud rates, or in the case of an 11/23 to set 
the boot configuration and other things.  See for example the images at

There's a group of pins with their jumpers to the right of the middle 
40-pin IC.  Look carefully and you'll see 5 (IIRC) other pairs, 
including one near the top left of the crystal oscillator with a jumper 
on it, and one with no jumper to the right of the smaller IC two rows 
above the main jumper group.  Other DEC boards such as DLV11J and the 
notorious (because of gazillions of jumper options) MXV11B do actually 
use wirewrap to such pins rather than jumpers, in a few cases 2-level wrap.


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