Atari Centipede Repair Logs
By: John Havel (Cmndr Brain) © 2021


Manufacturer: Atari
Game: Centepede
Year: 1980

This information is only from my own research and testing. This is not gospel. This information to here to help me organize and document my notes and repairs and to help others repair their boards as well. If you are reading this, use this information at your own risk. If there are mistakes that you are aware of please contact me at: srgntbrain@gmail.com

Atari Centipede constists of 1 main board (A037241) and a power supply (AR-II). The main board is powered by a 6502 cpu. There are 2 original chips. The "Pokey" at C3 and a video sync chip at P4.
The video sync chip, which is an 82s129, 74s287 or TBP24s10, is a (256 x 4) 1024-Bit TTL Prom. This can can be replaced with a burned 27c512 using an adapter.

I've discovered there are a some errors/revision corrections in the schematics that I have:

#1: Playfield Multiplexer

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#2: Synchronizer
Note: This does NOT affect the logic, just confusing when troubleshooting.

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#3: Video Output Circuitry

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#4: Trackball Erratic Movement

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Atari Centipede Boards

Boardset SN: 020211 (Rev. C)

Symptoms and Repairs:


• Edge connector burnt, Gnd.
  • Copper tape and solder to repair.
    
    
    
  
  
• No clock, missing 12.09Mhz crystal.
  • Replaced crystal. Clock signal is now good.
  
  
• No monitor sync. Displays out of sync image, can make out game playfield
  • Someone tried a hack on the sync Signals. Found a 74LS04 chip soldered to resistors R72 & R73. This hack tried to invert the HSYNC signal. The trace between the resistors was cut. Removed hack and fixed cut trace with a jumper wire.
    
    
    
    
    
  
  
• Result... 100% Working
  

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Boardset SN: 36229 (Rev. H)

Symptoms and Repairs:


• Won't boot. Blank screen, usually white, but sometimes other colors when reset.
  Test mode would beep 3 times.
  • Found memory at K7 and L7 pins 13 looked funny on oscilloscope. Trace broke/missing from M7 to L7 and K7 missing. New sockets and jumper wire on bottom.
    
  
  
• Game now boots, all motion graphics only on first line.
  • No output on any lines of 74LS163 at A5. Replaced chip.
    
    
    
  
  
• Archer will not move up.
  • Bad MC14584 at E/F11.
  
  
• No collision detection from arrow to centipede and when mushroom takes 4 hits, instead of going away, the mushroom would turn to a poison mushroom and take 4 more hits before disappearing. Poison mushroom would work correctly and make centipede dive down.
  • Bad Eprom at E1 (208). Verified bad when compared with known good chip. Burn new chip fixed both problems.
    
    
    
  
  
• Will not save High Scores.
  • Bad EARom at E5.
  
  
• Result... 100% Working
  

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Boardset SN: 025018 (Rev. E)

Symptoms and Repairs:
• Edge connector burnt +5v.
  • Copper tape and solder to repair.
    
    
    
  
  
  
• No crystal, no clock.
  • Missing crystal. Atari used 12.09Mhz crystals in Centipede. This gets stepped down so much, a 12Mhz cyrstal works just fine. Replaced with 12Mhz.
    
    
    
  
  
• All high score initials last letter would be the same as last letter of first initial. High scores would stay during game session but, would not retain scores after powered off.
  • Tried different EARom, no change. Turned out to be bad Eprom at E1 (208)
    
    
    
  
  
• Result... 100% Working
  

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Boardset SN: 010190 (Rev. C)

Symptoms and Repairs:


• No crystal.
  • Missing crystal. Atari used 12.09Mhz crystals in Centipede. This gets stepped down so much, a 12Mhz cyrstal works just fine. Replaced with 12Mhz.
    
    
    
  
  
• No chip at H3 74LS42
  • Replaced chip.
  
  
• No chip at P2 74LS163.
  • Replaced chip.
  
  
• No left or right (Horizontal) movement.
  • Resistors at R131, R133, R84 and R86 were changed to wrong values 6.7k ohms (Bl/Wh/Rd). Changing these values back to original values of 3.3k ohms (Or/Or/Rd) didn't fix issue.
    (A Brian emailed me and informed me that the 6.7k ohm resistors were correct. The change was a field service fix. *See #4: Trackball Erratic Movement above*.
  • Bad MC1458B at F11. Replaced chip.
    
    
    
  
  
• Result... 100% Working
  

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Boardset SN: 053443 (Rev. G)

Symptoms and Repairs:


• No sync, high pitched squeal out of speakers.
  • Wrong crystal frequency. Replaced with correct 12.096Mhz crystal.
  
  
• Ram at N7 was a 5101, different from all other ram chips which were 9101.
  • This was ok and didn't cause any issues, but changed to 9101 anyways.
    
    
    
  
  
• Screen covered with upside down red "A's".
  • Probing F7 and H/J7, no activity on pins 1-4 (pic1-pic5 data address lines). Signals into J6 74LS273 good, no signals out. Replaced chip.
    
    
    
  
  
• Motion sprites corrupt. Hit centipede segment would turn into a scorpion instead of mushroom and some spider sprites were wrong. Date and "Atari" on bottom wrong.
  • Test mode with watchdog disabled beeped 3 times indicating bad ram at k7. Replacing chip fixed the problem
    
    
    
  
  
• Result... 100% Working
  

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Boardset SN: 39060 (Rev. J)

Symptoms and Repairs:


• Green background with random black stationary characters all over screen.
  • Replaced 74LS42 at H3.
    
    
    
  
  
• Black screen except a couple of red dots.
  • No clock signal to CPU, no address signals. Clock circuitry working. 12Mhz, 6Mhz and 4H working perfectly.
    Broken pins, 74LS144 at C1 and 74LS144 B1 pins 4, 5 and 6 interally shorted and grounded.
    
    
    
    
  
  
• Playfield shows but, sprites not complete and some double images.
  • Touching the socket at H/J7 changed the screen image. Assumed cold solder joint. Replaced socket solved the incomplete sprite problem.
    
    
    
  
  
• Playfield now shows double images.
  • Test mode with watchdog disabled beeped 4 times indicating ram K5. Tested ram, good chip. Probing the chip revealed pin 3 (PFA1) was held low to all ram chips. Metering showed the PFA1 signal grounded. None of the chips were in sockets. All chips tested good. Socketed all playfield ram locations and ground was gone. Assume debris in chip pins? Reinserted all ram and issue was fixed.
    
    
    
  
  
• No left movement, right slow.
  • Replaced MC1458B.
    
    
  
  
• Result... 100% Working
  

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Boardset SN: 040085 or 07380 (Rev. E)

Symptoms and Repairs:


• Crystal Missing.
  • Replaced with a 12.096Mhz cyrstal.
  
  
• Hack job on controls section.
  • Removed hack job.
    
    
    
  
  
• VR1 and VR2 crushed.
  • Replaced both VR1 and VR2.
    
    
    
  
  
• Edge connector burnt, trace lifting.
  • Repaired with copper tape and solder.
    
    
  
  
• Missing ram chip at A6 27LS01.
  • Install socket and replaced chip.
    
    
  
  
• Blue screen. Pulsing sounds.
  • No signal on /Rom0, /Rom1 or /Rom2.
    
  • No output from74LS139 at J2. Raplaced, no change, chip tests good.
    
  • Found DB1 signal being pulled down. De-soldered and checked every chip that connected to DB1
    of course the last 2 chips, 74LS257 at M9 & L9 both bad.
    
    
    
    
    
    
  
  
• Random garbage on screen. Sometimes will change color when reset or power cycled.
  • Someone cut original trace and ran wire from chip at E3 pin 13 to trace on board.
    Most likely due to error in schematic. Original trace is /Write2 and wire was ran to trace for /Write.
    Removed wire and ran jumper to fix cut trace. Despite this having no changes, turns out the wire
    is a factory fix. Probably to fix an error in this board revision.
    The signal should be /Write2. Put wire back.
    
    
    
    
    
    
  
  
• Playfield shows, mushrooms and score are correct. Moving sprites only show in some vertical bands.
  As you can see in the last image, there are no memory errors.
  
  • Despite no memory errors, replaced 74LS257 at P7 in the Playfield Address Selector circuit.
    
    
    
    
    
    
    
• Result... 100% Working
  

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Boardset SN: 017177 (Rev. C)

Symptoms and Repairs:


• Dead.
  • Missing 7915 VR1.
  • No change, still Dead.
  
  
• Blank screen... sometimes blue/white w/ random characters..
  • Found decade counter 74LS90 L2 second counter circuit bad. This also prevented 6502A from getting reset signal.
  
  
• Random characters on playfield prevents game from playing. Memory issue?
  • Replaced and Socketed 2114 Ram @ F2.
  
  
• Kind of plays. Test mode 4 Beeps
  • 4 Beeps indicate Ram chip @ K5. Found broken trace, pin 3 between K5 and L5.
    
    
  
  
• Game now plays but with 1 graphics glitch and archer won't move up.
  • Defective counter @ B11, replaced.
    
    
  
  
• Plays, 1 graphics glitch. Flea always shows on top row and centipede shows over score when entering playfield.
  
  
  
  
  
  • Turns out, after de-soldering no less than 20 chips, it wasn't in any of the circuits I thought it would be. After, scoping and de-soldering every chip in the Horiz and Vert Motion Object, Picture Data Rom, Playfield Multiplexer, and Playfield Address Circuitry... Nada. Working my way back brought me to the Sychronizer.
    
    
    At first glance on the scope, this 74LS10 (3 input NAND) looks good.
    It had a pulsing output (green trace - 3 inputs are overlayed).
    
    
    But, when looking at the 74LS08 that it feeds, it seems as though the signal was not strong enough to register. So the 74LS08, 2 input AND, was only going low in response to one of the input signals. (funny, because the schematics show some sort of OR gate @ K4)
    
    
    After replacing the 74LS10, the 74LS08 now pulses correctly and blanks the motion objects on the score row.
    
    
    
    
    
  
  
• Result... 100% Working
  

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