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Atari Badlands arcade pcb repair

Two broken boards picked up on KLOV..  I knew they had some missing chips but I only had a quick glance and thought it was just the 68000 and 6502 CPUs plus some eproms.  On closer inspection though I found the custom Atari ‘LETA’ chip was missing.  That’s also used on more valuable titles like APB and 720 so most likely these boards had been parts scavenged at some point.  The LETA chip handles encoding of the steering wheel inputs to the game – but the game should still run without it, so let’s see what was up..

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With the CPUs and eproms replaced there was no video output and no CPU activity – in fact the CPU reset signal didn’t seem to be working either.  According to the schematics the reset depends on v-blank, which comes from the ‘SOS-2′ custom chip.  This chip only has a couple of inputs – the main video clock (14MHz) and an inverted 256H (scanline) signal.  The clock was good but the scanline timer stuck.  The non-inverted signal actually comes from the SOS-2 as well in a feedback circuit – so bad SOS-2?

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A replacement made no difference, but the trick is check what the signals are doing with the chip removed from the board.  The outputs should all be floating with nothing driving them (1H to 256H and 1V to 128V) – but 256H was still stuck low.  So actually the PAL @ 26R that takes 256H as an input had failed in such a way that the input was stuck low.  Replacing this PAL unstuck the timing, and there was now garbage video displayed – progress!

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With one bad PAL found I checked the others – and 3 of them became extremely hot extremely quickly.  These 3 were replaced and the game sprung into life!

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Still no inputs of course but JROK did design a replacement LETA chip which you can read about here http://www.jrok.com/project/leta/index.htm

I probably won’t go that route – adapting the game to use a regular JAMMA joystick sounds more interesting… for a future post.

Board 2

Unfortunately this had bad main RAM – pretty clear why as it was plugged into the board backwards and absolutely fried.  The RAM type (MB87316) is pretty rare – I think only used on Klax and a couple of other Atari games from this era.  I’ll shelf this board until some RAM turns up.

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