10
STAR*TECH JOURNAL/OCTOBER 1983
TROUBLESHOOTING SEGA'SFROGGER
By Jim Bender, Sega Electronics, San Diego, CA
This article contains information describing the major circuits of the game, and troubleshooting tips
that can help you repair your game ELECTRONICS more effectively. The logic board will be
subdivided into the following circuits: (a) Power-up reset circuit, (b) Video/ Object display, ( c) Color
circuit, and ( d) Sound and I/0 circuits.
The first circuit we will be discussing is the power-up reset circuit. For ease ofunderstanding, this
circuit will be divided into ( l) the timing, (2) reset, and (3) main program subcircuits. The main timing
for the board is an 18.432 MHz crystal. The signal is amplified and inverted by IC7 3 (LS368) and fed
over to IC72, where it is divided by 3 and a 6MHz signal is developed from pin 5 ofIC72. This 6MHz
signal is then fed over to IC7 3 pin 14 to be inverted and also toIC96 to develop the other major timing
signals. There are 18 major timing signals used in the game. They consist of9 horizontal signals, l H,
developed by IC76, 2H, 4H, SH, 16H, developed by IC82; and 32H, 64H, 128H, 256H, developed
byIC7l. The 64H signal is sent to IC66 pin3 where itis inverted andsenttoIC67 tobeAND-ed with
32H to develop a clocked input signal to pin 2 of IC79. Signal 16H is used to clock the input signal
through IC79, thus developing a syncv and a syncv signals at pins 5 and 6 respectively. The output at
pin 5 is sent to IC65 pin 9. The output of pin 6 is sent to IC96 to provide a clock to develop the 9
vertical timing signals. l Vis developed by IC96; 2V, 4V, 8V, 16V, is developed by IC95; and 32V,
64V, 128V, vsync are developed by IC84. The signal vsync is sent to IC65 where it is summed with
syncv and a signal called comp sync is developed. This signal then goes into IC27 pin 14 and comes
out as a sync signal, which goes into the connector, pin 814, and ultimately to the monitor. The
vertical and horizontal timing signals are also used to develop the LD signal through IC68; the C
blank, through IC53; H blank, through IC79; and the INT through ICB0. The vertical and horizontal
timing signals are also sent to a set of Exclusive OR gates, I Cs 70, 81, 83, 94, where they are gated
through by signals "VCMA" and "HCMPl" and a V 1 (Vprime) and HI (Hprime) are developed for
each respective input. The prime signals are used to provide the timing for the video display circuit.
The reset circuitry consists ofICs 67, 53, 69 and two transistors 23A697 and 2SC2320. When
power is turned on and the +5V is present, this will turn on the 23A697 transistor which will allow +5V
to flow to the base of the 2SC2320 transistor, which will then turn on and provide a ground at Diode
15588, allowing +5V to be felt on IC67 pins 12 and 13. The outputofIC67, pin 11 is then fed over to
IC53 pin 5 where it is gated by the signal VBLANK which comes from pin 6 ofIC69. The output of
IC53 pin 4 provides a signal called RESET which is simultaneously fed over to IC67 pin 9 and 10
where it is inverted and a signal called "RESET" is developed. This signal is used to provide a
RESET signal to both Z80s and also to ICs 35 and 7.
After all timing signals are confirmed and a reset signal is sent to the Z-80 (IC2), the Z-80 is
exercised and begins to address the main program EPROMs via the address buffers, I Cs 3, 4 and 14.
These addresses are fed over to ICs 5, 6, 7, 8 and RAMs, ICs 19, 20, 21 and 22. These RAMs are
used as scratch RAMs for temporary storage of information. The data for the EPROMs is then sent to
the Z-80 IC2, and to the other sections of the board through IC l ( data buffer).
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The next section we will be discussing is the video/ object display circuit. For ease of
understanding, we have subdivided this circuit into two subcircuits ( Character Position and Character
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Video).
First we will discuss the position circuit. The data from the EPROMs in the main program circuit
is sent over to the character position circuit which consistsofICs64, 63, 62, 39, 38, 51, 50,49, 48,47
and 37. The data is sentto I Cs 62, 63, 39 and 38 where they are gated through and into the position on
RAMs (ICs 50, 51) under control of the H prime timing signals from the timing circuits and IC64.
This information is written in and out of the RAMs under control of our OBJRAMWR signal which
TRACK BALL
ROLLER
comes from IC 15 pin 9. The information in the RAMs is read out and sent to I Cs 52 and 38. These
BEARINGS
ROLLERS
signals are then buffered and signals HPLA0 or HPLA 7 are developed and sent over to the color
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circuit and to the video display circuit. The Character Video display circuit consists ofICs 76, 77, 87,
3 Piece Assembly
.$1.99 each*
100, 97, 98, 99, 45, 75, 74, 85, 66, 65, 88, 81, 90 and 91. TheNPLA0orHPLA7 signals are sent
p/us postage and
$12.95 per set·
from the Character Position circuit to ICs 76 and 77 of the Video circuit. At this point they are
handling
/1-5 sets)
summed with signals" 1 V 1 or 128 1" and the output of these adders are senttoIC87. The output of this
THE SOLUTION FOR ...
D flip-flop is sent simultaneously to ICs 73, 100, 97 and 98. At IC73, the four Most Significant Bits
Centipede & Millipede Track Ball Problems
(MSB) are added together and inverted to provide one of the input signals to IC97. The Least
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.001" CONCENTRICITY
• Inaccurate Tracking & Movement NO WARPAGE
Significant Bits (LSB) from IC87 are sent to ICIOO where they are gated through by a signal called
• Loose Track Ball - Worn Rollers
THESE WORK'!
"OBJDAT A" which comes from IC45 pin 8. The outputs ofIC 100 are summed outputs; 0, 1, 2, and
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3. Summed (E) outputs 0, 1, and 2 are fed over to the color EPROMs for addressing. Summed (E)
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provides an input to IC98 and IC89 . I Cs 97, 98 and 99 provide the ten addressing signals for the video
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RAMs; the "Chip Select (CS)" and also from pin 7 ofIC97 a signal is sent to IC53 to gate the signal
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"LD" and develop signal "LDOUT" which is used to load the data from the color EPROMs into the
color RAMs. The data from the EPROMs are written in and out of the video RAMs by signals
Or Send Check or Money Order to:
VRAMWR, and VRAMRO respectively. This data is sent to IC90 and 89 where they are AND-ed
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with signals from IC88 to provide the addressing for the color EPROMs.
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IC88 interfaces the object position signals with the color circuitry.
Southfield, Ml 48075
The color circuitry inFrogger is very simple. The information is read out of the Color EPROMs,
Please send _ _ _ Track Ball Rollers
101 and 102 through ICs 104, 103, 91, 105 and 106, and into the Color RAMs, ICs 56, 57, 58,
I
Circle one: Cent - Milli.
I ICs
59 and 60 viaICs44, 35, 32, 36, 34, 46 and 45. The outputsofIC34 and 35 are alsosenttoICs 23 an
Please send _ _ _ Roller Bearings
Enclosed is Check or Money Order for$ _ _ _ _ I 24. The outputs ofIC24 are then used to address the Color PROM, IC25, which sends out your RED,
GREEN and BLUE (RGB) video signals to the monitor. The outputs of the color RAMs (DO) are
Mastercard# _ _ _ _ _ _ _ _ _ _ _ _
then fed over to I Cs 54 and 55 where they are inverted and fed back into the RAMs via I Cs 35, 32, 36
Exp. Date
Visa# _ _ _ _ _ _ _ _ _ _ _ _
and 34.
1
Exp. Date
The sound circuit is contained on a separate logic board (except for Moon Cresta type board).
• Signature _ _ _ _ _ _ _ _ _ _ _ _ _ I This circuit is for the most part an independent circuit and only interfaces with the rest of the game
I Name _ _ _ _ _ _ _ _ _ _ _ , electronics via IC7, which is used as an Input/Output Port for operator's control. The data from IC7 is
_ _ _ _ _ _ _ _ _ _ _ _ _ _
I Address
City/State/Zip _ _ _ _ _ _ _ _ _ _ _
Continued on next page.
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