The yellow GG is another one with Trace/Asic damage - Figures to be honest as half the twin Asic ones I have seen need a lot more work. First off it was one of those ones that like to turn on and straight off. Worked out that the 35v rail was pulling 5v low so given the fact the screen was smashed anyway I went ahead and removed the 35v circuitry. Ive now got the GG to red light stable boot and have managed to stabilise the 5v rail. This is good!
Next up I decided to check pre game ASIC operation, when you turn a GG on it should produce 3 signals without a game inserted, you should see VSYNC, HSYNC and CLK signals so last night I finally got the scope installed and started probing the board to see where we are at in terms of ASIC operation...
What a valid VSYNC data signal looks like:
This is HSYNC:
And our 3mhz clock signal:
With all of these valid signals being pumped out by ASIC B we can be pretty sure that this ASIC is functioning, next up I checked from the cart slot to VRAM and SDRAM on all other data lines D0 through D12 (Not the read lines etc just the data lines) and noticed that we have an issue with both D1 and D0 data lines between the VRAM and SDRAM, all other data lines we are seeing clean signals, basically we have a rusted out VIA so will need to run some Jumpers on the two data lines where we have a load of resistance that shouldn't be there. Being an early Japanese revision board there isn't a whole load of documentation but its super similar in terms of layout to early revision EU boards so im sort of using them as a baseline.
Next up I need to check all lines from the cart slot to SD/VRAM back to the ASICS so that is where I will focus next. Once we have all the core data lines up I should then be able to test a bit further but having removed all of the 35v circuitry I will need to do a screen mod on it anyway and that will take its time to come in from china... Still I am going to get the board working, reading carts etc before that comes in.
I also plan on probing the GG I broke to see where it all went wrong so will update this thread with details of that investigation as well, mind you I will need to recap it again as I removed them all when my other donors came in for mine and nutritions GG's last week. But yea the "silly" scope is super useful for these kind of repairs.
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