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Repairing your Space Invaders or
Space Invaders Deluxe Sounds
Space Invaders and Space Invaders Deluxe use a rather unique, if primitive, method for generating sounds. In the SI series, each sound has its own amplifying circuit as opposed to most systems where a sound is generated and then amplified in a common amplifier. The up-side of this is that usually only one sound goes, that gives you a pretty good clue as to what has gone wrong.
Each sound has its own operational amplifier (op-amp), most likely if you don't lose all the sound completely, the corresponding op-amp is bad. SI uses LM3900's, and there are quite a few on the SI board.
There are 7 basic sounds in SI, the missile shot, invader hit, explosion, saucer hit, saucer sound, bonus missile base and the thump-thump in the background.
Missile Shot Sound: Check the lm3900's at M4 and P4 If you get just a high pitch for the missile shot, check the 4006 at n5
Thump-Thump Background Sound: Check the lm556 at H4 This is a dual timer of the 555 series and uses a bus control to set the rate of the sound.
Base Explosion Sound: Check lm3900's at K3-4 and K5
Invader Hit Sound: Check lm3900's at K4
Saucer Hit Sound: Check lm3900's at M5
Saucer Sound: Check the 76477 at H2
Another chip to check if you just lose the saucer hit sound is the 74174 at E5 and the 7417 at F5, these can sometimes only partially fail with just one line going bad. I would suggest replacing these when you fix your board.
No Base Explosion Sound:
I fixed all of the other boards i was working on, but I have one more that has me stumped. I have replaced the lm3900's with new ones in location K3 K4 and K5 for the explosion sound, and even piggybacked another one on top of the new one, but its still a no go. I also checked for broken traces, and all seem to be good. All of the other sounds work great, but when you get hit by the invader I get a short pop instead of the explosion. All of the other components at K3 physically look OK, is there a certain resistor or anything that would cause this or something else that could be wrong?
Sounds like the random noise generator isn't working. IIRC, that's the 4006 and 4030.
Good call Mark, it was the 4006. I replaced it, and it fired right up Thanks for the help!!!
If you want to do some preventative maintenance on you SI to assure the sounds work well into the future, you will need 8 lm 3900's, 1 4006, one lm556, one 74174 and one 7417.
Replace the following LM3900's, M4, P4, K5, K3-4, K4, M5, M4 and l2-3. Replace the 74174 at E5, the 7417 at F5, the lm556 at H4 and the 4006 at N5.
Some things to check aside from that are the LM377, your 12v line, and the volume pot.
The problem was that the overall sound was VERY quiet. Even adjusting the volume had little-to-no effect on the sound volume.
My first thought was that it was the POT. I pulled it and tested it. 50K-->0K, perfect. Hmmmm, I thought. I put the POT back on and went back to your troubleshooting guide. While I was re-soldering the POT back to the board, and later while testing that the traces were still in place, I noticed that one of the legs of the POT went to one of the pins on an LM3900. Gee, I thought, that must be part of the overall, post mix amplification circuit. I had a hand-full of LM3900's laying around and decided to replace it just in case.
15 minutes later I had the new chip installed and plugged the board into the game. I coined it up and...
THUMP! THUMP! THUMP!!! Man, my ears were bleeding and my neighbors were WIDE awake!!! Did I mention I was doing this at 1am?
So, it appears the LM3900 connected to the POT is responsible for, at least part of the final amplification of the sounds. If you have a very "quiet" S.I. and it isn't the POT, replace that guy and it should clear up.
Faint Sounds Part 2:I had a similar problem. Speaker was OK. All sounds were proportionately correct in volume, just too quiet overall even with the volume pot all the way up.
I found that one section of the LM3900 quad op-amp
(that is used as a phase inverter to drive the bridged power amps) was bad. So
side of the bridge was driving i.e. half the voltage swing, therefore only one-fourth of the audio power. So even with the volume up all the
way it was still really quiet. That chip has two unused op-amps in it, so rather than changing out the chip I cut the three pins off the bad
section and ran jumper wires to an unused section. Works great now.
My Midway SI was working all the way except No sound at
all, I assumed Sound Board, I was wrong. I had 3 Power boards that I assumed
bad (jumbled video displayed), after adjusting the boards I got perfect video and game played great, but still no sound. I started poking
around one of the Power boards with a multimeter and found a bad diode, I replaced it and voila game works 100% Sound and Picture. So
without testing the other Power boards I just went and changed out that diode on the others and it fixed all of them. So if your game
plays and you have NO sound try replacing the single IN4004 Diode directly below the cable connector. Thanks