Hi guys,
I've been trying to repair this 16A for quite a while and I'm getting nowhere with it. I have the schematics but due to the fact it's hand drawn and written it's very confusing at times.
I've come to this section of the schematics regarding the LS174 ICs at the top left hand corner of the top board, next to the background graphics ROMs. I suspected IC102 was not working correctly as when I measured it with a logic probe, inputs 1, 2 and 3 (all on one side) are completely dead and the outputs are stuck on High, High and Low respectively.
I can't see any traces connecting these pins to anything else on either the top or the bottom, but the schematic seems to suggest these should be connected together in several locations.
The schematics make no sense to me in this area unfortunately, especially since I can see on the board itself that pin 14 of IC102 is connected to pin 10 of IC103, yet the schematic doesn't seem to reflect this at all. I thought for a while they may be referring to these pins as Output 1, 2, etc. but there are only 6 outputs, not 8 as suggested by this method.
Is anyone able to have a look and help out? I would like to try and figure out if these inputs should be connected to anything or if they are unused. It seems strange that they would go unused.
Picture of the schematic in question (The yellow highlighted box are the ICs I am questioning):
Full size version here: https://www.dropbox.com/s/4xo4y182ptaak8q/16aschematic.jpg?dl=0
I've been trying to repair this 16A for quite a while and I'm getting nowhere with it. I have the schematics but due to the fact it's hand drawn and written it's very confusing at times.
I've come to this section of the schematics regarding the LS174 ICs at the top left hand corner of the top board, next to the background graphics ROMs. I suspected IC102 was not working correctly as when I measured it with a logic probe, inputs 1, 2 and 3 (all on one side) are completely dead and the outputs are stuck on High, High and Low respectively.
I can't see any traces connecting these pins to anything else on either the top or the bottom, but the schematic seems to suggest these should be connected together in several locations.
The schematics make no sense to me in this area unfortunately, especially since I can see on the board itself that pin 14 of IC102 is connected to pin 10 of IC103, yet the schematic doesn't seem to reflect this at all. I thought for a while they may be referring to these pins as Output 1, 2, etc. but there are only 6 outputs, not 8 as suggested by this method.
Is anyone able to have a look and help out? I would like to try and figure out if these inputs should be connected to anything or if they are unused. It seems strange that they would go unused.
Picture of the schematic in question (The yellow highlighted box are the ICs I am questioning):
Full size version here: https://www.dropbox.com/s/4xo4y182ptaak8q/16aschematic.jpg?dl=0
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