Sega System 16 Board - Stuck on test?

So I got a bunch of System 16B motherboards that are mostly messed up, but I have this one that boots to the test screen (all dips are down..and I think it boots to the test screen with the test switch anyway). Anyway it does this for all games that I switch into it. Does this mean one of the TTLs is messed up on the test switch line?

Fox1 said:

So I got a bunch of System 16B motherboards that are mostly messed up, but I have this one that boots to the test screen (all dips are down..and I think it boots to the test screen with the test switch anyway). Anyway it does this for all games that I switch into it. Does this mean one of the TTLs is messed up on the test switch line?

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I don't have my system16 mobo on hand but yes you would start by following the trace back from the dip switch that toggles the test mode to the logic that addresses the dip switches. Once you found the chip pull up the data sheet and look at the truth table.

Look for I/O that are stuck or broken traces or damaged pull up/down resistors.

A multimeter is enough for diagnostics, a logic probe is what you should use and a DSO would be the best tool although over kill.