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Sega Mega CD 2 Region Free BIOS Repair Success


Spirited Member

Hello all.

I want to share this Mega CD repair I just completed.

I was sent a Mega CD 2 in which the person had attempted to install a region free BIOS chip. He was not successful and the console was just presenting a blank screen. I explained that I was not an electronics repairer and only had limited knowledge. However he insisted to let me have a look at it so that's what I did.

I started by testing the machine and sure enough the screen was black.

I opened it up and checked the fuse for continuity and it was fine. I then looked at the soldering of the chip and sure enough there was cold solder joints and what appeared to be missing pads.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7887-jpg.34473/" target="_blank"><img alt="IMG_7887.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29473-4d08a3f87e22146a941a99c0eccec359.jpg"/>

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7889-jpg.34475/" target="_blank"><img alt="IMG_7889.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29475-05169a923fbe0e6314caa2230ed3d8a7.jpg"/>

I commenced removing the BIOS chip using my desoldering station. This had limited success since too much solder had gone up the pins on the component side when the chip was installed. The thing was stuck. I decided to carefully cut the legs and remove it that way to avoid any damage to the board.

After cleaning up the area it is clear where the problems lie. Not sure how the original installer managed to scrape the solder mask like that. I guess those are pry marks. The original installer must have pried off the original BIOS chip which removed the pads with it.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7895-jpg.34477/" target="_blank"><img alt="IMG_7895.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29477-ae0f388d3a59174b12eec79b3e0dcc30.jpg"/>

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7897-jpg.34478/" target="_blank"><img alt="IMG_7897.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29478-7ae5f1cf5f923764de8ef8ef1841b095.jpg"/>

I installed a chip socket and a freshly programmed Japanese Region Free BIOS. I again tested the console and it was still a blank screen.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7903-jpg.34480/" target="_blank"><img alt="IMG_7903.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29480-d3673c90f272f26d2d2296f877d892a5.jpg"/>

I had a little look at the service manual but in the end everything I needed was right here on the forum at <a class="internalLink" href="https://assemblergames.com/threads/mega-cd-2-bios-repair.63195/">https://assemblergames.com/threads/mega-cd-2-bios-repair.63195/

I followed the images and painstakingly checked the continuity of all the pin destinations. I identified 10 pins that were not making any connection.

Pins 1, 17, 27, 28, 29, 31, 36, 38, 39, and 40.

I jumpered these connections to their destinations following the images created by wmi.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7916-jpg.34482/" target="_blank"><img alt="IMG_7916.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29482-6c954ef3d497018ba4e1395205009e56.jpg"/>

After this stage the console was still a blank screen. Some BIOSes loaded with Mega Everdrive would give an out of region warning, others were blank.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7922-jpg.34483/" target="_blank"><img alt="IMG_7922.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29483-d439952a4ee913ef0b1c15c1e1f79df4.jpg"/>

Soldering to these tiny vias is not for the faint of heart.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7930-jpg.34484/" target="_blank"><img alt="IMG_7930.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29484-1497e276bf1d27dd7ebcf647830c377e.jpg"/>

After this stage the console was showing a static image of the BIOS with no sound or LED.

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7939-jpg.34485/" target="_blank"><img alt="IMG_7939.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29485-ee96d4119bcad3adb2cbc629999bf3a0.jpg"/>

<a class="LbTrigger" data-href="misc/lightbox" href="https://assemblergames.com/attachments/img_7942-jpg.34488/" target="_blank"><img alt="IMG_7942.JPG" class="bbCodeImage LbImage" src="data/attachments/29/29488-9afe5c06314442771ca6fab1e424b14c.jpg"/>

After wiring up the final pin, number 36, everything loaded. I honestly did not expect this.

The region free BIOS correctly loads games from all regions and the Mega CD is working with all regions of Mega Drive.

I have had it running for the past hour on Sonic CD and everything is still working strong.

This was a one off. I am sticking to simple mods until I have mastered them and gained more knowledge of electronics in general. But, not bad for someone who has never done a single electronics repair in his life.



Dauntless Member

Great job, definitely not an easy mod for beginners and especially due to that tumor of a cartridge slot over the BIOS chip.


Spirited Member

Cheers. All credit to WMI for his guide. Without that map I wouldn't have had a clue. Would be nice to be able to work things out just from schematics and service manuals. Might take a few years to get to that point.

I need a better multimeter. My probes are intermittent. Very tough finding continuity when continuity in the actual probes is dodgy. Next purchase for definite.