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Atari Signature Analysis Service Manual

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    Page 1 1How Atari Signature Analysis Works Written by Phillip Eaton - inbox@phillipeaton.com *Comments and feedback welcome & appreciated* Revision 1.1 – 2001-09-20 · Updated contact links · Minor text changes Revision 1.0 - 1999-12-26 · Initial Release Introduction Ever wondered what all those 4-digit ‘signatures’ are, that are dotted around the Atari circuit diagrams? They are used for diagnosing game PCB faults with an Atari CAT Box. They are useful because, armed with a CAT Box and a game...
    Page 2 2Basically, the CAT Box has it’s own processor which then can control the game PCB address & data bus, using the PCB’s clock signal. It can then be used to address individual areas of the board for checking individual components, using the knobs and switches on the CAT Box control panel. So now you know what a CAT Box is, you have a problem – you don’t have one. So why should you bother reading any further? Well, you might want to read on because you’re interested, but there are other reasons....
    Page 3 3 Figure 2 CAT Box Counter Circuitry This is implemented by four cascaded 4-bit counters on two 74LS393 ICs. The 74LS244 ICs are used as buffers onto the address bus. (Note there appears to be a bug in the Atari diagram – the second counter on IC B5 appears to be cascading itself! If you understand the diagram, you should be able to spot the easy fix.) Why is discrete hardware used to cycle round the address bus, when the CAT Box has its own 6502 processor, and can address all of the PCBs address...
    Page 4 4 Figure 3 Start, Stop and Clock Probes
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