Well, right next to the ADB connectors is UL11, the magic ADB chip, F1, a 1 amp fuse to +5V, a surface trace to L1 inductor network pin 3, the other end of the inductor is pin 6 opposite side L1, goes to ADB pins 3 +5 out.
Check F1 first. If good, check continuity inductor pin 3 to 6. If inductor is blown pins 1,8 are a likely spare. Pin 1 is the one next to the fuse.
ADB ground is filtered by L1 pins 4,5
ADB signal is filtered by L1 pins 2,7
Avoid damaging UL11 with static-touch the nearby ground rail first.
Look carefully at nearby Q3, a surface mount 2N3904 that can get eroded to crap by leaking fluid from C13. Also all surface traces near C13.
Check underneath to make sure that R31 470 ohms, R32 4.7K , R33 27 ohms are intact.
C72 .01 uf and C73 33 pf need to not be shorted.
Check soldering of ADB connector blocks.
There are several artwork layouts so your mileage may vary...
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