Neo Geo CD

Hi all, looking for a little help if possible. I have here 3 Neo Geo CD's. Two have completely dead mobo's and were bought as faulty for spare parts (previous owner tried to install a unibios and damaged pads and the board). I have bridged tracks and pads but they are dead. The third one the board works fine. I don't have an original PSU i am using an external HDD psu (not one of the cheap chinese molex ones) that gives out 5V@2A, 12V@2A & Gnd, the original psu socket was removed and a 3 pin din socket was put in its place. The console boots up fine and will load a game disc fine, i can then play or leave on rolling demos for hours and it will be fine. After a little while though it all seems to give up, if i turn the console off and then back on the disc is detected and i get the press start flashing but every disc shows the loading progress bar and then black screens. this is the same until i turn the unit off for a little while and let it cool down. I thought this may be a laser issue so swapped that out, same thing happens, can play for a few hours and then everything boots to a black screen. Tried a different drive controller board, same issue. I have tried another video.power board and again it boots fine and plays but then gives up again.

Anyone have any tips that might help?

Thanks

Anybody?

Does anyone think a Unibios might help here? If so can anyone offer a wiring diagram for the CD Unibios? I understand its a 27c400 eeprom, Is it just a straight 1-1 wiring to the original bios pads? I have the ability to burn the chip (the 3.2 free version from razoola's site) and i am no stranger to soldering on smt parts having done numerous mods on retro systems including complete bios replacement on sega multimega/cdx systems.

Thanks

Before messing with the BIOS, I'd look at the power more carefully. When electronics behavior change over time, I usually start looking at the capacitors. The stock caps are old, and if that board has had non-standard power run through it (with the different PSU connector) then the old caps also likely had to filter power levels they weren't engineered for.

My recommendation: replace the caps, and maybe also swap the non-standard power connector back to a stock one off of one of your spare dead boards. Use an SNK stock power adapter also with fresh caps and try it all again.

Sounds like you are using burnt discs and wearing out the laser.

Is it possible that using 12V instead of 10v overtime is giving these issues? I might recommend putting a voltage regulator in line with your power supply output.

haightc said:

Is it possible that using 12V instead of 10v overtime is giving these issues? I might recommend putting a voltage regulator in line with your power supply output.

Click to expand...

No, the voltage regulator can accept voltage range of 7-25 and some are 8-12v so either model falls in that range.

Thanks for all the tips, i don't have access to an original psu and they are quite expensive so can't test it with one. I have used one of these HDD psu's before with a different neo geo cd and that worked fine. I will try recapping it next and will replace the laser with a new one.
As a side note though, does anyone know the pinout of the original onboard smd bios chip so i can fit a unibios. I can't hurt to try it.

Regards