Many of us know Bas - TC - but I just wanted to share what he's done for me and my dead NeoGeo CD - Bas - hope you don't mind. It just goes to show exactly what this forum is all about and why I can't stay away. THANKS TC So much appreciated.
From TC
Finally got your NeoGeo repaired, good news I hope...
After removing the old encoder and fitting socket strips in its place I plugged the new chip in to get the same fault symptoms..
Yesterday I finally got the scope onto it....
All digital signals were present and correct from the cpu board which is great news and were reaching the pins of the encoder socket with no problem, all other signals required ie, colour burst were also correct, but nothing was appearing on the output side of the chip once fitted..
Now according to the data sheet for the device, it uses split rail power supply and separate grounds to isolate inputs from outputs and give a better performance.
The +5V on the output side was prexsent and correct but the input side was only registering 1.4V hence the ic encoder was not actually being powered correctly...
Tracing back through the circuit an inductor is used to filter and supply that input feed and it had gone very high in value, also the regulator supplying it was not providing enough voltage.
Replaced the +5v regulator with new component and fitted compatible replacement inductor and now both supply feeds to the input and output were present and correct..
Fitted the encoder ic and the system now displays perfect video and sound....
Board cleaned up refitted, also checked and plugged in original encoder ic and that works fine too.
I have left the new chip in the unit but pls keep the old ic for spares as you may need it in future, thanks to a socket now in place its easy for you to swap and change the chip in the future if needed...
Quite a bit of work but excellent results in the end my friend...
LEGEND m8, pure bl00dy LEGEND
Z3
From TC
Finally got your NeoGeo repaired, good news I hope...
After removing the old encoder and fitting socket strips in its place I plugged the new chip in to get the same fault symptoms..
Yesterday I finally got the scope onto it....
All digital signals were present and correct from the cpu board which is great news and were reaching the pins of the encoder socket with no problem, all other signals required ie, colour burst were also correct, but nothing was appearing on the output side of the chip once fitted..
Now according to the data sheet for the device, it uses split rail power supply and separate grounds to isolate inputs from outputs and give a better performance.
The +5V on the output side was prexsent and correct but the input side was only registering 1.4V hence the ic encoder was not actually being powered correctly...
Tracing back through the circuit an inductor is used to filter and supply that input feed and it had gone very high in value, also the regulator supplying it was not providing enough voltage.
Replaced the +5v regulator with new component and fitted compatible replacement inductor and now both supply feeds to the input and output were present and correct..
Fitted the encoder ic and the system now displays perfect video and sound....
Board cleaned up refitted, also checked and plugged in original encoder ic and that works fine too.
I have left the new chip in the unit but pls keep the old ic for spares as you may need it in future, thanks to a socket now in place its easy for you to swap and change the chip in the future if needed...
Quite a bit of work but excellent results in the end my friend...
LEGEND m8, pure bl00dy LEGEND
Z3
