May 1997
STAR*TECH JOURNAL
ROWE BC-3500 BILL AND COIN CHANGER
INTERMITTENT PROBLEMS
Kerry Messana
Games Technician
Waterford, New York
In the past few weeks I have had
several calls regarding this model
changer. Two turned out to have
intermittent power supply prob-
lems. The complaint was:
a. No +5 volts
b. No + 12 volts
c. No +40 volts
This may seem odd at first glance
because they are totally indepen-
dent supplies. However, there is
a connection. The +40 volts will
shut down if there is any kind of
malfunction including empty
hoppers. This is normal and it
basically disables the machine.
The +40 volts is controlled via a
relay on the power supply board
(Kl).
This relay is controlled by the
computer and the computer de-
pends on that +5 volts to run, no
5 volts and it will sit there doing
nothing hence the +40 volt relay
will not be energized shutting
down the +40 volts. Ah, there's
the connection!
As it turns out the problem was
actually in the + 12 volt circuit.
There are two 4 70 ohm 2 watt
resistors (RS & R6) in series with
a 15 volt 1 watt Zener diode. This
circuit creates a voltage reference
which is fed to a 2N6055
Darlington transistor (QI) setup
as a pass transistor. The transis-
tor provides current amplifica-
tion. The output of this circuit is
the + 12 volt output of the power
supply and also the input voltage
to the +5 volt regulator.
I had found that the solder pads
at RS and R6 were cracked and
one of the pads had broken loose
from the rest of the trace. I pulled
the resistors out and checked
their value. After finding both re-
sistors within spec, I scraped the
leads to get a good connection
and went to work on the board.
On the board I scraped the coat-
ing off the trace that should have
connected to the pad that was
broken. I then re-installed the
resistors and attached the lead at
the broken pad to the trace itself.
This fixed the whole problem in
the + 12 and +5 volt circuits.
Following this, I gave the board
a good eyeball and touched up
some other solder joints that were
beginning to crack. One that had
already cracked was R7, a resis-
tor used to bleed the 12 volt cir-
cuit on power down.
After final inspection, I
re-installed the power
supply and the machine
came back to life.
I reset the computer and verified
all the settings because intermit-
tent problems with the +5 volts
could cause errors to be intro-
duced to the non-volatile ram
and that baby stores setup info.
An error there, if undetected,
could possibly cause the machine
to give more or less than is right.
I ran some bills through the ma-
chine and everything seemed to
work fine. A little bum-in time
and the customer was called to
come and pick it up. The second
changer was brought in and the
same procedure was performed.
Seems like the machines were at
an age where problems might
start showing up on the power
supply. All the parts that broke
loose were heavyweights and vi-
bration from normal machine
operation had eventually broke
them free. I guess this is some-
thing to watch for.
Be advised, the parts listings re-
ferred to in this article are as they
listed them on the PCB itself. The
schematic shows it as an 8:XX
number. For example, R7 is listed
as R807, R16 as R816. Also,
when resoldered, always remove
the old solder first. This will in-
sure a clean solder connection
and if it isn't removed, it will be
noticeable.