Neo Geo CD Service Manual / Schematics? Controller Port Fault

[GadgetUK]

Does anyone know of any links to these - assuming they exist?

A friend has posted a problem on YT where his up input on both ports is not working. Assuming that the Neo is reading the P1 and P2 inputs in the same way the NEO C1 does on the MVS and AES, then it has to either be a missing data line, or faulty path somewhere in between. I see a NEO BUF - that's my first thought, but thinking about it I don't see how that would be possible unless the controller ports were in parallel.

Anyone seen this problem before on the Neo CD?

EDIT: I see from the photos a couple of 74 logic chips - I am thinking one of the gates has failed in one of those. At a guess, each port has its own NEO BUF chip, and since the up dir on both controller ports doesnt work, it must be where the 74 logic feeds the ribbon to the motherboard.

 

[Xian Xi]

The NGCD controller board gives weird problems even when a cap goes bad.

 

[GadgetUK]

Thanks! I've got him to send just the controller board - I will test all the inputs via the 245's and what ever else is on that PCB first, but it sounds like he might need to send the console if that board checks out OK =/

 

[mikew]

At a guess, each port has its own NEO BUF chip, and since the up dir on both controller ports doesnt work, it must be where the 74 logic feeds the ribbon to the motherboard.

Hi GadgetUK, the directional controls share the same NEO BUF chip, here's a schematic: https://wiki.neogeodev.org/index.php?title=File:Neo-cdd3-1.png .

Each NEOBUF chips is 2 245's in a custom SNK package. In this case, all 4 share the same bus terminating at J3 but have different enable pins so only one can be active during a controller read. I bet the single line that handles the 'UP' button requires attention.

 

[GadgetUK]

Hi GadgetUK, the directional controls share the same NEO BUF chip, here's a schematic: https://wiki.neogeodev.org/index.php?title=File:Neo-cdd3-1.png .

Each NEOBUF chips is 2 245's in a custom SNK package. In this case, all 4 share the same bus terminating at J3 but have different enable pins so only one can be active during a controller read. I bet the single line that handles the 'UP' button requires attention.

Thanks!!! I had seen the NEO-BUF was just 2 x 245's and hoped they would be routed through the same chip. Fingers crossed its a faulty gate. I am also hoping that not all 16 gates are used and if I am lucky I might be able to just patch it to an unused gate. I figure worst case I could dead bug a 245 and use 1 gate on it, or maybe take a NEO-BUF from an old 1 slot I have and swap it out completely. Will see how things go. Thanks for the info and the link =)

 

[mikew]

I figure worst case I could dead bug a 245 and use 1 gate on it, or maybe take a NEO-BUF from an old 1 slot I have and swap it out completely. Will see how things go. Thanks for the info and the link =)

You might be able to just swap the two NEO-BUF's if the UP line isn't used on the other one. I did that once and although it worked I wasn't careful with the heatgun and nearly roasted that board. Besides being old, the quality of those boards is questionable and its a different material than what's used on the motherboard PCB with much less tolerance to heat.