PDP-11/23 Debugging

Dave G4UGM dave.g4ugm at gmail.com
Sun Nov 9 03:33:36 CST 2014

> 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
> http://store.reuseum.com/DEC_M8186_F11_Fonz_CPU_Processor_Board_
> Q_Bus_p/000021514002g14store.htm
> There's a group of pins with their jumpers to the right of the middle
40-pin IC.

On that pic those links look like a DIL socket, not wire wrap pins. But if
wire wrap pins are used like that its not surprising they work loose. 
I would expect them to be plated steel and therefore have characteristics
that are bad for soldering. That is:-

1. Have a relatively large mass as they need to be stiff to wire wrap
2. Therefore have a large thermal mass or heat capacity
3. So they are slow to heat up -> may not get hot enough to solder
4. Slow to cool -> likely hood of dry joints  if they move while cooling
5. Poor solder whetting as they can be hard to clean....

So not surprising they sometimes work loose. 

> Look carefully and you'll see 5 (IIRC) other pairs, including one near the
> left of the crystal oscillator with a jumper on it, and one with no jumper
> 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
> options) MXV11B do actually use wirewrap to such pins rather than jumpers,
> in a few cases 2-level wrap.
> --
> Pete

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