7
STAR*TECH JOURNAL/SEPTEMBER 1983
The "Bear" Facts continued.
OK, last but not least is the formula for finding the total capacitance in a parallel circuit. The
formula for finding CT in a parallel circuit is the same as is used for finding RT in a series circuit.
I
_l.
I
Cl
Cl..
l
C3
T~- - -T~_"I_M_~_
o _ J ..____
3M_F_o---'T IOMFD
Cl+ C2 +CJ= CT 4uf+ Juf+ lOuf= 17uf
See how simple that is?
OK, now using Ohm's Law, find the current in the following circuit:
~~7
R~
IT= ?
Well, if you are confused, let me help. First find your RT ( remember your first formula). Then I or
current equals E or voltage divided by R or resistance (total).
I=~
RT
So, your answer should be 3.75 milliamps. Yes or no? If you said yes, you're correct. If you said
no, try again.
Next, we will find the total current in a parallel circuit. As before, you must know the RT first
Then you can fmd the current being used in the circuit
llvdc
ffi"'"
First find RT using:
1
1
1 = RT
Rl + R2
1
1 = 821.429 ohms
1k + 4.6k
1
Then you fmd your current using:
12vdc
IT = ~
= 14.609mA
RT
821.429 ohms
The only reason that I showed you how to fmd the total capacitance right now is so that you can
relate it directly to finding total resistance. You simply reverse the formula when working with series
resistance/capacitance, and parallel resistance/capacitance. I want all of you to become comfortable
using this formula, because next month we will start using capacitors and resistors in circuits along
with the 555 timer causing an RIC time constant circuit Until then, practice! We will also learn more
about series and parallel circuits.
OK, on to the technicians info.
We started a four-part series on troubleshooting non-video arcade games last month, by giving you
a list of common failures in power supplies. This month, we're going to give you some information
concerning digital sequential logic. If you have a "down" game and you've checked the power supply
outputs and they're good, the following steps should be taken.
1. Make sure that all connectors are undamaged This includes making sure that all wires are
unbroken and that all pins are securely seated in the plastic connectors and that all pins are free of
tarnish and/or corrosion.
2. Make sure that all connectors are securely seated on the logic board and/or that all plugs and/or
connectors in the wiring harness are in good shape and are making good contact
3. You will need to test each microswitch individually using your ohmmeter. If any microswitch
shows any sign of being sticky or not always making contact internally when tripped or activated,
replace this switch as a preventive measure at the least If the game or unit works to a point, then stop.
Check to see what limit or trip switch should be making contact at that point This switch tells the unit
that it has accomplished a set function and it is ready to go to the next step. If the switch location or
switch is faulty, and is not being tripped or making contact, correct this switch placement or
replacement switch and try again.
If all of the above is working correctly, you will need to test your motors, solenoids, clutches,
brakes, etc .... and that will be explained next month.
Now, I know that everyone is going to gripe at me about there being no game review and very little
fix-it information this month, but I'm doing the New System Preview this month on Cinematronics'
Dragon's Lair. Since it is not a complete video by conventional standards (the graphics are not
computer-generated) this falls into a hybrid category of non-video and video. So, turn to the New
System Preview if you haven't read it already and eajoy.
Continued next page.
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