Models and Prices
Related Sites List
ISA Bus Sources
Wiki Main Page
Servo To Go, Inc.
8117 Groton Lane
Ph: 317 257-1655
Timer (U14, 82C54 or 71054C) Lock Up on Model II
Due to noise on the clock signal going to the input of timer 1 and possibly
timer 2 (jumper configuration), the timer can lock up. This can be seen as
interrupts not being generated after a short time or a period of even
2-3 hours. The increased noise may be due to one or more of several factors,
but not limited to them. Some possible reasons are: changes in part manufacturers,
changes in production of chips, changes to the programming contained inside
the PLD, or changes to the socket containing the PLD. The fix is simple to
implement. Solder a 220 ohm 1/4 watt resistor between pins 12 and 15 of the
timer chip (U14). This increases the current draw enough that the PLD cannot
provide the current required at full voltage (~5V), so the output high voltage
is reduced to around 3.50-3.75V. This inturn reduces the signal bounce to
a functional level and the lock ups do not occur.
If you have other issues that you would like to see discussed here,
drop us a note.