Sega: G-80 system

The Sega G-80 system is a neat little modular system which separated game hardware between boards (for example, sound was on one board, video control on another, etc).

The vector games by Sega all run on this hardware set up, and it has been documented fairly well. The raster stuff is not as well known, but the following links should help you some.

Links

The Sega XY FAQ
Sega G80 Hardware Reference

Universal Sound Board

To find problems, try this test:
From Dan French:

For the duration of this "Test", we'll need to remove external input (remove it from the possible problem). Cut R7 at one end, and bend it up a little, making sure that it won't reconnect (you will need to reconnect it later).

When this is done, confirm the continued existence of the problem by re-testing the game. You should still have the problem, but the other sounds should not be active. If this is not the case, then stop.

(if you don't know what channel it is on)
Next, lets find out what channel it is on. For these steps, you might want to devise some form of easy "jumper on jumper off" as we are going to go through a binary sequence, and cutting and resoldering could get tedious. Cut R42, R43, and R44 in similar fashion to R7 above. You will need to follow a binary sequence with these to determine what channel the problem is on. Using the chart below, add/remove connections for R42/43/44 in sequence to determine which channel (or all three) the problem is on, where 1 indicates "on" or "connected" and "0" indicateds "off" or "discconnected".
R42R43R44
001
010
100
011
110
101
111

If disconnecting a certain resistor always causes the problem to go away, we can deduce that circuitry after output from U22 (pin 1) is "ok".

This test was used to solve a problem where "static" existed for some sounds, but not all. It turned out that U29 (analog/digital converts) was the problem.

Editor's note: The above example is for debugging the Sound Block 2 section of the Universal Sound board; you can do the same trick for the other sound blocks, just figure out what the right resistors are. This is a good debugging tip; I have used it myself.

Eliminator sound board/Space Fury sound board problems

The schematics pretty well define the audio circuits for each sound. Most sounds have entirely separate circuits for each sound, so it is easy to determine the set of parts to check. If a specific sound is bad or missing, I would start with replacing any electrolytic capacitors in the circuit first. This typically fixes the problem.

Symptom: Eliminator sound board: Thrust in background. Small Explosion cuts out all audio temporarily, then audio becomes restored after 15 seconds.
Fix: Replace CA3080 at U6

Symptom: Eliminator sound board: Electrons are all at the same pitch (high).
Check 74LS374 at U34 to see if it is addressing correctly. Replace Q11.

Astro Blaster missing "enemy fire"

On some Astro Blaster sound boards, there is no enemy fire because the factory did not install one of the resistors. If you look near the middle of the sound board near the 4-pin connector end, you should see 2 1M resistors. If you only see 1 1M resistor and 2 solder points next to it, insert a 1M resistor to restore sound.


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