Ground TP 17. In the schematic, TP17 is pin one of U3, connected to
+5V thru a 47k resistor. On the circuit board, TP17 is on the display
side, just right of the lower-right corner of the IC. Grounds are about
1/4 inch below and to the right, the three non-tinned points in the large
area of metal. TP17 is the tinned pad next to a SM resistor marked '473'
I rigged a momentary switch to ground TP17 thru a 1k resistor (you never
can tell) and it works just fine! I drilled a small hole to mount the switch
just above the plastic depression so I could push the button with my right
thumb. A small toggle switch would fit.
I'll be trying the other TP's to see what wonderful things RS didn't put
on the front.