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Time Soldiers arcade PCB repair

Bought as a non-working board for $9.99 – the most obvious problem is that no CPU was present so clearly the game wasn’t going to do much without that!  With a replacement 68000 in hand (again from Ebay for only a few $) the game booted to garbage.

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A logic probe on the CPU address and data lines showed zero activity, so the CPU clearly wasn’t doing anything.  Power and ground tested as good.  The reset and halt lines on the CPU were pulsing, so it seemed something on the board was trying to kick the CPU into life.  Testing the CLK pin on the 68000 showed it to be stuck low.  I traced out where this pin went and it connects to the output (Q) of a LS74 next to the oscillator.   The logic probe seemed to show this chip had failed, as a CLK was pulsing on the LS74 input, but the outputs remained stuck (one output feeds back into a LS74 input, so the output should toggle hi/lo every clock in order to form the 68K clock).

Tested off-board – failed – replacement from Dragonninja parts board soldered in – board boots right up!  Quickest TTL level fix I’ve ever done.

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At first I thought there was a graphics problem as the title screen was corrupt – though it’s strange all of the other screens were perfect.  Then I remembered I’d seen this a long time ago in MAME..  If you boot the English language ROMs with the Japanese dipswitch enabled the title screen is corrupt (because it expects the Japanese character ROMs).

Unfortunately this board is stuck in Japanese – because the dip-switch isn’t being read by the software.  A previous owner has removed resistor packs for the dip and the jamma inputs, presumably to repair something else!

That shouldn’t be too hard a fix – to be continued.

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