STAR*TECH Journal
July 1993
Prince's Corner
Donald B. Prince
D&RMusic
Bozeman, Montana
ROWE
OBA 2
CREDIT PROBLEM
PROBLEM
We have recently found a prob-
lem that has plagued us for
some time. We had been re-
ceiving complaints that five
dollar bills were only giving
out four dollars worth of credit.
At first I thought that it was a
hoax, but when the location
said that they had seen it hap-
pen, I started to investigate.
SYMPTOM
The problem, as we found out,
occurred in machines with
OBA 2 type bill acceptors
which were set up to take $1
and $5 bills.
CAUSE
Finding this failure was very
time consuming, because the
problem did not happen con-
sistently every time, and
didn't happen at all on some
units. With the aid of a logic
analyzer and some time, we
traced the problem and came
up with a reason for the symp-
toms.
Referring to Figure 1, you can
see the pulse train from an
OBA 2 control unit at different
points in the circuit -as
marked. The pulses should be
30 msec widths and 50 msec
between pulses as shown in
Figure 3, but the first pulse is
only 6. 6 msec as seen in Figure
2.
' . .. five dollar bills were
only giving out four
dollars worth of
credit."
For some reason, as yet unex-
plained, the first pulse is not of
the right duration, thus the
logic connected to it fails to
recognize it as a valid pulse.
This is the reason it is $1 short
on it's credits given.
The pulse problem can be
traced directly to the OBA 2
processor, but replacing it has
proved unsuccessful in solving
the problem. The real kicker is
that this failure may occur
only once in $500 or not at all.
This problem doesn't just hap-
pen on $5 bills, I have seen it
happen on $1 bills as well. The
symptom for a dollar bill is
that you get no credits at all,
since the logic fails to see i~
pulse that short.
SOLUTION?
Presently, there is no fix. If
your customers are complain-
ing about being shorted, your
unit probably has this timing
failure. But, be sure to check
out all other possibilities be-
fore assuming that timing is
the culprit.
If you have any questions
about this particular problem,
call Tom Minardi in Engineer-
ing at Rowe International 616/
243-3633. Rowe has been
made aware of this problem
and of all our findings, includ-
ing copies of the timing dia-
grams. Materials were sent o~
April 30th of this year. We'h -
keep you posted on any devel-
opments from Rowe.