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O2 Fixer

O2 Fixer

Our price:

35.36 PLN

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Weight: 0.2 kg

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O2 fixer is a replacement for 74LS08 chip in all Atari XL/XE machines. It provides four additional BO2 signals that provide option for separation Atari chips on the BO2 (Buffered O2) clock bus. It also lowers the parasitic capacitance on the BO2 path on the motherboard. Idea by Piotr D. Kaczorowski, design/production by Lotharek.

Device solves (hopefully...) all problems with o2 timings in ATARI 8bit computers. 





  • pcb is very small, 402 elements used, 8 x 1G08 AHCT used. 







Installation in 65xe (other ataris the same steps):


1. Locate 74LS08 chip on the motherboard. If it is socketed, skip point 2 below.





2. Desolder it  and solder back 14pin socket (not supplied)




3. Insert O2 Fixer into the socket. Make sure that it is oriented properly.  4 soldering pads at the PCB should be next to pin 1 



4. ATARI shall start as usual. TEST IT

5.  Locate O2 signal from the CPU on O2 Fixer: with the multimeter check for the continuity from pin 39 on the CPU to subsequent pins of the fixer. For most XE machines and 1200XL it is pin #1, for Atari 600XL it is pin #5, for 800XL - pin #12, but for 800XLF, it is pin #2.

6.Connect the located pin with a wire or a bit of solder to the middle pad called O2_IN.


WARNING: My atari is 65XE !  others may have o2 signal at diffrent pin 




From now on, the soldering pads marked OUT_1, OUT_2, OUT_3 and OUT_4 will provide 4 buffered and noise free O2 signal outputs. You can use them for:

  • BO2 signals
  • Ultimate 1MB connection
  • cart slot O2 signal replacement - this is most suggested use, resolves problems with fast cartridges like SIDE 3.1
  • connecting PIA O2 / POKEY O2 signals


More info:

  • 3 of 4 outputs has been connected to GND with 680pF caps. look at the bottom side.
  • Ultimate 1mb O2 signal needs no capacitor - please use TOP ONE output
  • If You use "capped" output and atari behaves odd, remove corresponding capacitor.
  • I suggest NOT SOLDER o2 fixer to ATARI board. Please, use socket in case of need removing capacitor of desired output

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