Neo Geo CD

[scrappysphinx]

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

[scrappysphinx]

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

[ShootTheCore]

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.

[Xian Xi]

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

[haightc]

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.

[Xian Xi]

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.

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

[scrappysphinx]

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