Mar 042015
 

Today I received a batch of some faulty PCBs and among them there was an original Altered Beast boardset:

Altered_Beast_PCB

Once fired up all was working fine except for the colors, they were clearly wrong (kinda pinkish):

colors_issue

For first I went into TEST mode.In all Sega System16 games(that support it) you can enter in TEST mode by pressing down at same time TEST,SERVICE and P1 start switches.But color RAM test was passed successfully:

Color_RAM_TEST

Near the two 6264 color RAM @J9 and J10 I noticed a couple of 74HC273 which input were connect to data BUS of the RAMs (as they latch input data).Probing the one @L11 revealed some outputs stuck HIGH though inputs were toggling fine.Piggybacked it and colors came to normal (well, almost, sky apart) :

colors_piggybacked_74HC273

Time to desoldering and testing it out-of-circuit:

74LS273_out_of_circuit_testing

Replaced it and board was 100% fixed.Job done.

 

 Posted by at 8:22 pm