Pac-Land repair log

Got for repair this original Pac-Land PCB (manufactured by Namco and licensed to SIPEM) :

The board was in very good shape but it booted all the time to a static screen :

Probing the program ROMs revealed the /CE line of two devices were stuck HIGH or silent :

The signals come from a 74LS139 @7D :

Being a Fujitsu TTL I was aware of the way they usually fail so I didn't spend much time on it.I removed the device, it miserably failed the out-of-circuit testing :

Replacing it allowed the board to boot, game was fully playable but backgound graphics were all blocky :

The issue was obviously located in the tilemap generation and, judging from kind of fault, more precisely in the addressing circuit.Schematics show there are a couple of 74LS86 @9J and 10P that generate some addresses to the backgrounds ROMs :

Devices were again from Fujitsu, they gave troubles when tested in circuit with my HP10529A logic comparator :

They both failed the out-of-circuit testing :

I replaced the two TTLs and powered the board up again sure enough it was fixed and fully working but playing a game I noticed sprites were glitched :

The sprites circuit consists in a couple of custom ICs ('CUS11' and 'CUS12'), four EPROM devices and some logics where I spotted another Fujitsu TTL, a 74LS377 @7K :

The scope showed output pin 9 was floating despite an active input :

Device failed the out-of-circuit testing in that exact gate (pin 9 was, indeed, in 'Z' or high-impedance state)

The replacement finally cured the board.Repair accomplished.