Most likely due to a defective batch of IC6 ( 74HC132 ) used on the front PCB
(the inputs on these does not discharge the capacitors connected to their inputs properly as normal versions of 74HC132's do)
Remedy: Please replace IC6
TC item code: 455013011 SN74HC132DR SO14
The defective batch of chips was used on units with serial numbers in the range from approx.: 3111660 to approx. 3112640
- We have, however, seen this problem on units out of the range above; i.e. 3112733